Ham Radio didn't start with Appliance Boxes! The Art of Troubleshooting Updated 3-05-2023. PIN Diodes

Troubleshooting a Project!

Update 3-5-2023. PIN Diodes Installed!

Noticeable power output improvement on 10 and 15 Meters and have made contacts on those bands. Still issues with 160M. Receiver sensitivity is much improved on the higher bands. 

Installing the PIN Diodes is best described like an actual tryst with the 250-pound Mary Jo in the back seat of the 57 VW Beetle. The purchase of a dental mirror sure helped the process -- with the PIN Diode install not Mary Jo.

73's

Pete N6QW

Update 3-1-2023. PIN Diodes

The three UM9401's arrived from RF Parts! Total Cost $14 EACH. Not for the faint of Heart!

[This TR-7 Resurrection project is now a link on the N6QW website. https://www.n6qw.com/]

For all you Mackrell Snappers like me (Catholics) it is FAT Tuesday!

Update2-21-2023. The Capstone!

The TR-7 Final YouTube Video has been uploaded but thought a summary of this journey may be in order. The TR-7 is a marvel of Engineering and was a leading-edge product of the 1970's.

Top View of the TR-7 

Let us start with the "Negative Aspects" of this product. It is compact -- too compact as this makes servicing a bigger problem than shoehorning the 250-pound Mary Jo into the back seat of the 57 VW Beetle! 

To properly service this radio, you need a set of specialized tools and test boards which 50 years later just are not that easy to obtain. The concept of DFMA (Designed For Manufacturing and Assembly) while employed by the Japanese, was still foreign to American manufacturers. 

The documentation while extensive has failed to include the tribal knowledge common at Drake but not known by someone picking up the manual some 50 years later. I went nuts trying to find how to set the bias on the final (200 Watt) amplifier stage. There is no bias setting but not clearly stated as such. 

This TR-7 Resurrection is not for the faint of heart nor should it be undertaken by a person who has only a passing knowledge of electronics. A repair/restoration has to be thought of in terms of months not days. There are resources to assist you, but they too may not cover the problem you have. 

No receive or transmit and a "wonky" display reading should have triggered: "look at the VCO voltage on Pin XXX and also look the   one place where 24 VDC is generated". To writ large I did find it and that did cause me to really learn about the TR-7 Block diagram but that was almost 6 weeks of work.

The Test/Alignment Instructions (Section 3 of the Service Manual) must have come in several flavors (versions). The initial Transmitter alignment has several steps where adjustments are made to the 2nd Mixer Board and the Pass Band Tuning Board. These are TFMS (Tune for Maximum Smoke) adjustments. 

The 2nd Mixer Board in the manual does not match the 2nd Mixer in my early (S/N 1394) TR-7. There is a Top Cover over many of the Boards (including the 2nd Mixer and PBT) that have access  holes for board adjustments. The access points are numbered like C705 or L101. These are not the ones required for adjustment in the manual. So, I need to find an early manual. The earlier photo, above, shows the boards with the cover removed.

This was a DRAKE problem in their documentation. I remember Gary Barrell (SK) who was assisting me with a TR-4 radio problem was rabid to know the S/N of my radio as there were I think 4 versions of the TR-4 schematic and you needed the S/N to get the right schematic. 

I am plagued with an issue of transmitter output across 1-30 MHz. The output on 160 Meters is very low and a simple CW waveform subjectively has more ugly than Gravel Gertie (a comic strip character married to B.O. Plenty). The CW waveforms on all other bands appear normal. But the power output beyond 20M is like a weak stream of RF. I wonder if there is something like an equivalent of Electronic Viagra.

I posted the problem on the Drake reflector and received two very excellent answers that affirmed that where I was looking likely was the cause du jour. One suggestion involves pulling the band switch shaft which is like over 10 inches long. The problem in doing that is that you could get the switch wafers misaligned where the band switch is not in synchronization and best described as getting Mary Jo and her full-figured twin sister into the 57 VW Beetle backseat both at the same time. 

The two bands where operation seems most normal are 20 and 40 Meters. But with Cycle 25 heating up I do hear stations on 17, 15, 12 and 10 Meters. That would be nice to work those stations with the TR-7 but the weak stream of RF on these bands does put you at a slight disadvantage. But more importantly I note that the received signal levels appear lower on these bands. This might signal a problem with the high-power Pin Diodes.  Yes, shaft removal to fix these. 

A couple of more days for the video. But my plan is to keep poking away at the Transmit power issue. But we have come a long way with a radio given me on Dec 25th that didn't receive or transmit and had a wonky display of numbers.

73's

Pete N6QW

Update 2-19-2023. Soon A Final Recap of the TR-7 Project.

I hope to prepare a final YouTube video that recaps the TR-7 project. That will take a bit of time, so you might not see fresh postings for several days.

However, in my latest attempt to keep you, the blog readers, ahead of the curve, a ham friend (Dean) alerted me to a sub-variant of chatGPT that can create art based upon what you tell it.

My first thought was a painting of the 250-pound Mary Jo in the backseat of the 57 VW but thought that might be too hard. So, my instructions were to show me (with a few years removed --well more than a few) sitting at my work bench "brewing up a storm".

N6QW ~ This is what you need to do!

My three sons at one time had a garage band and so I asked to see a painting of the band.

This chatGPT feature (DALL - E-2) can provide hours of adult entertainment. Here is a how to do it link for your dining and dancing pleasure:

The-DALL·E-2-prompt-book-v1.02.pdf(dallery.gallery)

I did test the Mary Jo suggestion and got two versions. YL, 250 Pounds, 18 years old, back seat of a 57 VW.

Mary Jo, Back Seat 57 VW

One thing for certain -- there isn't much room in the back seat of a 57 VW.

73's

Pete N6QW

Update 2-18-2023. The TR-7 Thread will soon end! 

The transmitter portion works but not consistently across all bands. To wit (or writ large) the power output on 10 Meters can be set to 90+ watts but on 15 and 17M (common but different BPF constants than 10M) the output is 60 Watts.

Tracking this issue down will require a lot more study and research to determine the why. This might make for boring reading and likely not something I can spend days on end following the breadcrumbs. But if I make any substantive progress, I will break in. The thought of removing the band switch shaft and pulling the Low Pass Filter is like the thought of a 3rd trip to South Vietnam in 1967.

Like Mary Jo and the backseat of the 57 VW an unconventional solution was ultimately found. If you fed her a Bob's Big Boy Hamburger 1st at the Miracle Mile in Monroeville -- that was the answer.

73's

Pete N6QW

Update 2-17-2023. TR-7 General Coverage Operation.

This is so cool. Cut one circuit board trace and the TR-7 will transmit on all frequencies (1 to 30 MHz) and the use of the Up / Down 500 kHz Toggle buttons can only happen on certain band switch positions. Thus, the Band Pass Filtering is in concert with the frequency range being used for transmitting.

I did a quick test and saw output on 17 and 12 Meters but have made no measurements. TBD.

The TR-7 was one heck of a design in 1970! That my friend was 50 years ago! BTW $1 in 1970 is worth $6.94 today. The Sell Price of the TR-7 in 1970 was about $1365.00. So today that is more expensive than an Apache Anon weighing in at $1365 X 6.94 = $9,473.10. With a power supply and other accouterments, that today is a $10,000 station.

73's

Pete N6QW

The Maiden prayed for a Knight in Shining Armor, but what she got was a night with a skinny runt who had no money! This is a parable to describe what it is like to purchase a Parts Only, Tech Special TR-7. But the next morning the Maiden did have a smile on her face!

The Answer to Yesterday's Quiz is:

Kimberly Guilfoyle

 

Addendum to the 2-16-2023 Posting. How cool would it be to do FT-8 with a TR-7?

I created a design for a Digital Interface to add WSJT-X to any USB capable SSB Transceiver. No one much gave a crap, so once again I want to bore you with that design. It will be a link on my www.n6qw.com Website.

For me I just need to dig my interface out of the storage box and the Computer of Choice would be the Atomic PI Developer's kit converted over to Linux Mint 20. These still are available from Jeff Bezos for $50 and a lot less cost than a Raspberry Pi4!

Pete N6QW

Update 2-16-2023. More Contacts on the TR-7

Yesterday I had two more contacts on 40M with no signs of instability or "wonky" looking signals. The reports were from two hams who actually know me and were positive with good reports of signal quality and good sounding audio.

I have done some tweaking of the ALC Pot and the Pre-Driver Gain Control Pot. The Power Output is 100 watts.

73's

Pete N6QW

Update 02-15-2023. More Evaluation?

Yesterday only had about two minutes and tried 40M loading into the Delta Loop Antenna. No instability or oscillations were observed So, this is going to be one of those rabbit hole searches.

There, the blog has indeed been updated.

This is Point Roberts, WA and one of 3 places in the USA that can be only reached by driving through a foreign country to get there by land -- Yes, you will need a passport to drive there from the rest of the US. With only about 1000 people, it is #37 on the list of donations for a guy currently under multiple investigations based on $/1000 people. It is a hotbed of conspiracy theorists and also rumored that 32 residents are in the witness protection program!

Quiz of the day: What does the Governor of California (Gavin Newsome) and Donald Trump Jr. share in common? This is a shocker!

73's

Pete N6QW

Update 02-13-2023. First Contact on 20M! It is alive!

Yesterday afternoon (I am not a sports fan), after some extensive further prodding and poking I decided to hook up the Final Brick to the Dummy Load. With the Pre-driver Gain and the ALC set for 100 watts, I looked at the output using a Snoop Loop connected to my DSO. [For the BTE's that is the Digital Storage Oscilloscope.] The pattern looked clean. 

Switching from the Dummy Load to the Antenna I could hear some signals on 20M at 14.260 MHz. It was one of those ARRL Sponsored Stations giving out points for a contact. The station was in Oregon and had a small pile up. It seems if you contacted him, he was worth 225 points. 

In fairness to the ARRL Contest and seeing only 50%* of US Hams could contact this station, I moved off of frequency, found a spot and hit the Microphone button after a short listening period to make sure I was not stepping on anyone. 

Upon hitting the microphone button, I announced, "This is N6QW checking the Frequency -- is this Frequency in use?" The whole purpose was to check the signal waveform while connected to the antenna. It was all good! Now to QSY back to 14.260 MHz.

This ARRL shadow station had a small pile up and it took at least 5 or 6 calls, but he responded back to my call. He gave me a 5X9 (everyone gets a 5X9) and then I announced this was my 1st contact with the TR-7. He came back with the TR-7 is a great rig and it sounds really nice! He added a footnote that I should be sure to collect my 225 points. 

This was an abnormal situation for me as I don't collect points and always try to avoid the ARRL Sponsored stations. It was also abnormal that I put a rig on the air that I do not feel is fully functional on all bands. It works on 20M but the problems with the other bands still exist. 

In fact, the same test on 40 M showed hints of an oscillation most likely caused by the 30 feet of poor coax I am using at the remote bench connected to the normal operating position junction box and the lack of grounding of the rig at the remote bench. On 40M it works FB into a Dummy load. 

The issues with 10/15/160M have not gone away. But after 7 weeks the urge to put the TR-7 on the air was too great. So, now in earnest I need to map out a detailed plan to fix the transmitter so that it functions properly on all bands. Now an even bigger incentive since I have made one contact on 20M.  But as a caution to me No More Contacts until it is fixed!

* Only 50% of US Stations have HF Tickets. You too can check this at the ARRL website -- of the 770K licensed US hams, only 388,000 have HF privileges.

73's

Pete N6QW

Update 2-12-2023. Fun With Data!

Yesterday we took data across the ham bands and looked at the output from the High Pass Filter and at the output of the Pre-Driver Stage. The initial results showed a variability in the output from the High Pass Filter at the High and Low Ends of the bands but somewhat flat in the midsection. A good way to look at the data is the Voltage gain of the Pre-Driver Stage to ascertain if that specific stage is a contributor to the problem. We already know a huge disparity coming out of the High Pass Filter. Using Excel, we are able to manipulate some of the data collected yesterday.

Looking just at the Bands & DB (Voltage) Gain

The above graph is a bit of a reverse as it shows the Bands on the bottom scale (in reverse starting with 10 Meters and going out to 160M). The vertical scale is the Gain of the Pre-Driver. The amp has higher Gain on 10/15M as well as a bit of gain on 160M. But in the middle section it is flat.

But hiding in the bushes are some observations and conclusions. Firstly, the Voltage readings are in Peak to Peak. For the purists who would take the PTP values and convert them to RMS by taking 1/2 the PTP and then multiplying it by 0.707, that is not required as we are taking a ratio wherein those added math operations cancel out. For a voltage gain after taking the log (at the base 10) we must multiply by 20. 

If we look at the curve from the 80M Band to the 160M Band, we see a small movement upward. Well gang that is 3DB and so that is significant. 

If we look at the Voltages coming out of the Pre-Driver Stage, we get less power output on 160M as well as 15 and 10 Meters. In fact, that is the case with the Final Brick installed. Keep in mind that we see lower Voltages are feeding the Driver and Finals. So less exciting RF in means less out!

Also, of note the Pre-Driver is doing a great job of amplifying the signal. It is what is being generated ahead of this stage that has a lower output on 160, 15 and 10 Meters. A noted Observation is that 15M is less than 10M and possibly an issue with the High Pass Filter Board on 15M.

Thus, we need to look at the stages ahead of the High Pass Filter (2nd Mixer, Transmit and Pass Band Tuning Boards) as these have adjustments. But we must also poke at the 15M High Pass Filter. One of the critical Transmitter Tuning Steps is done on 10 Meters. Finally a look at the output from the High Pass Filter and this is a concern because 10/15M are from the 2nd VCO. Thus, I need to check the signal Level of the 2nd VCO.

What is also telling is that what is shown as the output of the High Pass Filter as compared with the Final Brick connected are somewhat analogous and suggests the intermediate stage are OK and the Final Brick may actually be OK!

History is repeating itself -- it was a 38 cents voltage regulator and not any bad boards. Likely there is something similar with the transmitter circuits.

73's

Pete N6QW

Update 2-11-2023. Amos and Andy.

The Amos and Andy Show was a popular radio program ((1928 and Pre-TV) which eventually made its way to the small screen. One additional character was "The Kingfish". Today that program might be considered culturally insensitive and perhaps even racist. But one show segment came to mind when thinking about the TR-7. 

This show had the "Kingfish" in the real estate business who was trying to sell Amos (or Andy) a home that had a wall missing in the bathroom and exposed to the outdoors. To accommodate the situation the Kingfish suggested getting a shower curtain and a bathrobe of the same cloth. Thus, when Amos (Andy) was in the bathroom it would look like a shower curtain that was moving. The deal, it was a low price.

The TR-7 transmitter anomalies are much like that shower curtain -- it was a crude attempt to hide the fact that a wall was missing.

The TR-7 seems to provide full Power Output on 20 and 40 Meters, but significantly less on 10/15 Meters. Keep in mind a different VCO for 10/15M. The output waveforms are OK 40M on up but look ragged on bands below 40M. 

Some conclusions might involve the Low Pass and High Pass Filters. Somewhere in that mix is Pin Diode switching and one caution by some who have repaired the TR-7 -- just hope that is not the issue. But it also could be issues with instability on certain bands. I think at some point the Final RF Brick was redesigned and that is a clue. Since mine is S/N 1394 it may be of the first vintage RF Brick.

The early computer axiom "garbage in is garbage out" is a clear guide. I need to first look at the band signals at the output of the Pre-Driver and compare all the waveforms and the power levels over the HF bands. 

If we can see all is clean and reasonable, that the circuitry up to that point including the High Pass Filter is NOT the suspect circuitry. That limits the issues to the Driver, Finals and the Low Pass Filter. 

40M HPF

40M Pre-Driver Output

40M SSB Waveform

160M Pre-Driver Output

I am not sure what this data might be telling us. Yes, there are waveforms out of the HPF and these are being amplified by the Pre-Driver and they for the most part look OK. But the variability suggests that the TR-7 works best on 20/40M and not so good at the other ends. This is outside of the Driver and Final RF Amp.

One other test is to inject 3 Volts PTP from my signal generator into the Driver and look at the output of the Final RF Amp. That would check the LPF and the Driver/Final stages. I will look at that test.

It might be easier to find a home with all walls in place! (BTW the Original Amos and Andy radio characters were not African Americans. Freeman Godsend and Charles Correll disguised their voices to not sound like two white guys.)

73's

Pete N6QW

Update 2-10-2023. It might be that I found the transmitter issue. But this morning it might not be true!

Using the DL2MAJ process shown in the two videos in the earlier posting, I did some testing yesterday of the Pre-Driver stage. The process involved uncoupling the Pre-Driver from the Driver Stage and terminating the Pre-Driver output with a 50 Ohm resistive load. The Christmas Tree Pattern looked OK. But the output voltage was not even close to 3 V PTP. 

I next looked at the schematic and spotted R2210 which is a board mounted 100 Ohm Trim Pot. It was cranked way back. A bit of a tweak and Boom more than 3 volts PTP. A prior owner must have had some reason to do this. Seeing we were getting enough drive and leaving the 50 Ohm resistor in place I reconnected the Driver Stage. 

The output on CW now is 100 watts and on AM with carrier insertion is 100 watts. This tells me that the Driver Transistors are good as are the Final Transistors. This does not substitute for a full transmitter alignment but gives me hope we can have a working transmitter portion without some major repairs.

This TR-7 Resurrection is moving right along. I now need to do all of the steps in Section 3 of the Service Manual which covers the full TR-7 alignment.

However, a reaffirmation of yesterday's test did not show the same results this morning. So likely there are some heating issues to chase down. So close but so far away!

73's

Pete N6QW

Update 2-9-2023: The Roadmap of the Transmitter Repair.

A bit of earlier research turned up these two YouTube videos (below) from Stefan, DL2MAJ. What he saw on the TR-7 he was repairing is not unlike what I saw on the brief amount of transmitter testing I did on S/N 1394. 

1. Initially I did have a problem with the PTT not working and on VOX it sounded like a Buzz Saw. That was a wiring issue with the 4 Pin Plug to 3 Pin Stereo plug. I used the adapter I had built for the Yaesu FTdx100 --not the same Pin wiring issue. That is now fixed, and the PTT works, plus the audio has cleared up but at most about 60 Watts on CW. Clearing of the audio does not mean a quality signal. The most you can get on AM with full carrier and no modulation is about 10 watts. The pattern on CW is not a pure Sine Wave but more like a Jagged Tooth Wave. (For those who watched TV in the early 1950's -- Think of Kukla, Fran and Ollie) The SSB Christmas Tree Pattern suggests non-linearity. But this was only a quick peek, therefore I need to do a more detailed and rigorous evaluation. 
2. Part 3(5) shows some initial tests out of the UP Converter / Pre-Driver which I need to undertake and Part 4(5) gets into the Brick RF Amp. 

Stefan has provided an excellent Trouble Shooting Fault Tree Analysis, and this will guide my next 6 weeks of work. I have bought a batch of 2SC1969s and have a transistor tester which appears to be the same one he used for hfe testing.

Also Note the Turntable that Stefan uses to move around the radios. I bought one of those and need to build the assembly.

We have moved the needle on the TR-7 Resurrection with the Receiver working and a bit of RF coming out of Transmitter. I am hoping the finals are good and the only issue is the driver stage. 60 Watts on CW versus "0" is a good sign. Mary Jo is headed toward the backseat of the 57 VW Beetle.

From the top edge of the Brick, you can see one of the Driver Transistors and it looks like it has been "tampered with" (Tack Soldered) and the P/N doesn't look like anything recognizable. A Clue?

73's

Pete N6QW

Update 2-08-2023: The Transmitter!

Now, having a working receiver my attention has shifted focus to the transmitter. But 1st was a short stop with the PS-7 which I assured myself it was working before powering the TR-7 and possibly smoking it.

My quick Transmit tests revealed the following:

1. The Radio works FB with VOX but with PTT you can key the transmitter but no audio. I used a 4 Pin Adapter to 1/4-inch stereo and possibly the wiring is not correct. With VOX all you need is the Microphone circuit to be proper. 
2. The output is possibly 60 watts under whistle conditions. and about 15 watts with AM and carrier. Again, the same problem no audio on PTT using AM. Above is the final RF Amp Stage. These transistors are no longer available, and neither are the driver devices although there are substitutes (2SC1969).
3. The Christmas tree Pattern looks like a Shaggy Dog or a Hairy Orangutang!

DL2MAJ has a series of you tube videos and one of them is dedicated to the RF Amp Brick. His initial test results are not unlike items 2 and 3. His cure involved new RF devices and some parts changes. That likely will be a path I need to follow. So, now to find a matched pair of 2SC1969 RF transistors. RF Parts no longer carries the 2Sc1969 and DL2MAJ ran into the same issue. So, he bought a transistor tester and found two from a purchased lot that had very close hfe's. I have the same transistor checker, so I now get to use it.

I foresee another 6 weeks before we can declare victory on the Transmitter. Stay tuned.

73's

Pete N6QW

Updated 2/07/2023. Success!

The 78L24 Voltage Regulator arrived and was installed in the TR-7. It is now operating on Receive! A little sample for your dining and dancing pleasure!

You can see this project has driven me nuts!

Next, we will focus on the transmit section with an interim stop to check out the FP-7 Power Supply.

Update 2-06-2023. Ordered MC78L24.

Order placed with Mouser and new cost $1.11 each based on Product Cost and Shipping + Tax and Tariffs. Mouser has advised a possibility of 1 to 2 days delay based on crap weather! 

Their throw to the wall and hope it sticks prognostication is a Thursday 2-09-2023 delivery. This is now pushing 2 weeks for a simple part.

So, Guess What shows up after placing the Mouser Order?

You Never Can Win! But the 78L42 will be here in my hot hands TODAY!

Pete, N6QW

Update 2-05-2023, What would you do?

Most likely anyone reading this blog has ordered parts from one of the major Internet based suppliers and we get the "Track Your Package Here" message. Well, this order from Digi key is small about $14 and was originally ordered a week ago on 1/29/23. It got shipped out on Monday 1/30/23 and has disappeared into a black hole. Noteworthy it took 4 days to post a message that it is late but in transit somewhere. Two days later (Sunday) THIS is the latest update.

So, a call to Digi Key could provide no further information than what you see. The nice sounding YL who answered the call said: Well, the cost is small we will just ship you out another order. Let us know.

The unit cost since I bought 10 pieces is 38 cents each. Now my dilemma is what to do next? If I have Digi Key replace the units then that parcel will go into same system that lost the 1st order. 

Then I looked at other suppliers such as Mouser, Newark, Jameco, All Electronics etc. for the 78L24 which is the TO-92 form factor of the regulator. Surprise! That P/N is not easy to find as it is not carried by all suppliers nor in stock by others. 

The question du jour is what should I do? I guess one option is seek the relief of a second order from Digi Key and then think about buying the stock 7824 (larger physical size good for 1 amp) and adapting that to the board.

The one shop who does have the 78L24 as a stocked product has none in stock but awaiting delivery. Ha, these must be on the same truck as my Digi Key order. I did check Amazon, but you have to buy a kit pack with various other values of regulators and cost almost as much as my total order.

Who would have thought a component that costs $0.38 could cause so much upheaval. What would you do?

Now a tale that offers a counterpoint to the above. Facts be facts and that is the XYL typically uses an adult bib when eating. I noted yesterday that the stock was down to about 6 pieces so time for a reorder from Amazon. 

Last night I placed the order at about 9 PM and got the usual thank you for your order. This morning I heard a bit of noise at my front door about 5:30 AM. I gulped hard as we had been robbed once before and that is when I heard my phone ding. "Your order has been delivered." That is about an 8 hour turn around versus a week with a small packet of parts that as of now we have no idea if it will ever surface.

 

One answer might be to have Bezos buy out Digi Key and then we would have overnight delivery of our precious parts!

Still no fix of the TR-7 and blame it on Digi Key!

73's

Pete N6QW

 

Update 2-04-2023. No Parts Yesterday!

My LM78L24 Regulators are on a truck last seen in Thief River Falls MN. No Further Update. They were scheduled to be delivered on 2/03. No one knows any updated status at Digikey.

I did remove the 78L24 on the power supply board and sure enough it is toast! I also saw 50 VDC (unloaded) into the Input side of the former LM78L24. So, the DC-to-DC Inverter is working!

I also replaced C2108, and noteworthy its predecessor looked slightly smoked. I upsized the voltage rating from 25 VDC to 50 VDC. 

Getting the two devices installed on the heat sink is like "installing" Mary Jo into the backseat of the 57 VW Beetle -- there isn't a lot of room. So, the circuit board has been prepped as such that when the replacement arrives, I only need to lift the power supply board from its 12 pin Socket, slide in the new device, solder it up and back into the card slot. 

But as added protection so I don't smoke anything, the lead coming from Pin #2 is floating (but insulated from anything else). So, at power on I want to see what is coming off of Pin #2 and then if it is 24 VDC it will be soldered back on to the main motherboard.

Saw a great video on Amazon Prime Video, about Motown Music and how it started. Gordy worked at Ford Motor Company and while on the factory floor learned about the Ford Production Process and Quality Control. 

Each week he would hold a Quality Control team meeting and collectively they would listen to the music produced that week (yes Motown used a Production Line Process). Then a thumb up thumbs down vote determined if each song would be released to production. At times the particular song might be rearranged, or a different group selected to actually sing the song. But it was a deliberative quality process versus throwing things on the wall to see what sticks. Thus, we must see the Voltage at Pin #2 before we smoke the VCO!

We are close.

73's

Pete N6QW

Update 2-03-2023. Power Supply Fix!

Yesterday the C2108 replacement capacitor arrived and today the LM78L24 will hit the mailbox. I will follow the plan that was previously outlined. I am hopeful this will do the deed. By the end of today I will know if that is the fix!

I have some thoughts about how to alternatively generate 24 VDC and that includes not spending $70 for a new board. One approach which I consider viable is the use of a Mean Well 9 to 18 VDC Input to 24 VDC output DC to DC Inverter Module. This jewel is 2.5 inches square and only 1/4 inch high. I have used this model in another radio, and it works FB. It is good for 600 milliamps at rated voltage and has an isolated output. 

Stay Tuned!

73's

Pete N6QW

Update 2-02-2023. Fixing the Power Supply Board!

Parts are on order to replace the 24 VDC regulator and there are couple of electrolytic capacitors also on the Power Supply Board that are in the queue to be replaced. Parts will arrive today and on Friday (2/03) so perhaps by the weekend we can have the 24 VDC fixed. If the inverter transformer is bad on the 24 VDC winding side, then we will have to think about a purchase of a replacement power supply board. I have been told this transformer is the "weak link" on this particular board. 

The Repair Process.

We all repaired stuff and we all have broken things while undertaking "a simple repair". This power supply board is headed toward the unobtanium list and therefore a little forethought (like foreplay) can yield huge dividends with a happy ending.

The internal power supply board is not just a simple plug-in board but has two devices that are tethered to the board and are mounted on the chassis which acts as a heatsink. These devices are a LM7805 Regulator and a 2N5689 Pass Transistor (PNP). These must be unbolted from the chassis. Careful as the 2N5689 has a Mica insulator -- don't lose it! As DL2MAJ points out in his videos, put the mounting nuts and bolts in a safe pace as you will need these for the re-installation.

Once the board is free and located on a safe place on the work bench, using your headband magnifier carefully look over both sides of the small board. Look for any discolored parts which indicate smoked parts and also observe any parts that appear cracked. Time also for some continuity and part value checks. (Resistors that are out of tolerance.)

As noted, insure you have continuity from the Inverter transformer to the Bridge Rectifier on the 24 VDC circuit. With your DVM check that you have continuity to the bridge rectifier from the transformer secondary. An open circuit is cause for no 24 VDC. You will want to actually perform this test right after the board inspection. 

Based on our research and from what we have observed we want to replace at C2108 which is a 220 Microfarad, @ 25 VDC electrolytic capacitor which has been defined as a typical failure. The other part is the LM78L24 Regulator. 

I believe it is possible to test the power supply board outside the TR-7 by supplying 13.8 VDC to the input Pin (#9) and to Ground. 

Since C2108 is hung on the 10VDC Rail which supplies the Inverter circuit it is on the critical path. As a 1st on the list, we will replace this item before doing any other work!

Once the capacitor is replaced next would be a simple test starting 1st by removing the 78L24 from the board. Next with your DVM in hand measure the resistance from the output of the Bridge Rectifier to Ground to see if it a dead short. Assuming it is not shorted then a quick power on to see if there is juice from the secondary / bridge rectifier to the input pin of the 78L24. If you see that on your DVM, then install the replacement 78L24. Keep these tests very short as the 2N5689 Pass Transistor and the LM7805 are not on a heatsink. Short is like less than 5 seconds. 

In the hopeful non-event you do not see voltage to the input pin of the regulator that suggests a problem with the inverter transformer or the bridge rectifier. 

After installation of the 78L42 you should see 24 VDC at Pin #2. All OK then re-install the power supply board starting first by reinstalling the two devices on the heat sink. You might want to add some heat sink compound and DON'T forget the mica insulator on the PNP pass transistor. 

Once all back, power up and all should work. Take a quick check to verify that you have 24 VDC on Pin #2.

My free set of 1940 Cadillac Hubcaps story is haunting me where for another $100K you can find the rest of the car parts for a complete restore. In the end -- it will still be an 80-year-old car or 50-year-old radio. When this is all done, it is like Mary Jo is in the backseat of the 57 VW Beetle!

73's

Pete N6QW

Update 2-01-2023. TR-7 on FT-8!

Frequencies are in sync!

The purpose of the above test is to show as you move from the Low VCO to the High VCO (the transition point being 15 MHz) the same frequency would show up on all of the bands. As you move thru the switch positions 40, 20, 15 and 10M FT-8 frequencies are tuned to the comparable FT-8 frequency (XXX074.0).  Thus, the VCOs and the frequencies are in synchronization. Did you catch the subtlety of that test? A later test would be to set the FT-8 frequency for 10 Meters and after a suitable warmup period and check the drift.

I ran this same test on a Ten Tec Omni C and rifling through the band switch positions did not show up on the LCD Display as the same XXX074.0 for each position. The difference is a Phased Locked VCO versus crystal mixing for the various bands*. Indeed, the TR-7 was the FLEX 6400M of the 1970's.

* Sort of like using a Si5351 PLL versus an Analog VFO or PTO in our homebrew radios.

73's

Pete N6QW

Update 1-31-2023. It was the 24 VDC Supply!

When you Know Stuff, You Can Do Stuff!

Next steps are to fix the internal 24 VDC power supply board and do the alignment. It is indeed a bright day!

This was a major troubleshooting effort on a radio I really did not know much detail. While I have had several TR-7's in the past, the earlier units worked and thus never required looking at the details of the innards. If indeed this radio can be fixed with the simple replacement of a 75 cent 78L24 three-terminal regulator, then the prior owner probably doesn't want to know that information. 

1. I will now proceed to evaluate the Power Supply board for the issue with the 24 VDC. I think that I can pull the board out of its header socket and wire 13,8 VDC to it and check the circuit if it is solely a problem with the 78L24. I suspect it is as the - 5VDC appears at Pin #1 leading me to assume a working DC to DC Inverter. 
2. Once done with #1 then I would proceed to align the receiver section. 
3. Finally, I would start to look at the transmitter stages. Undoubtedly, we will face many new challenges.
4. We are likely several weeks away from having an on the air rig. But the 1st big hurdle has been crossed.

73's

Pete, N6QW

Update 1-30-2023. I Found it! (Maybe)

In the 1970's there was a Born-Again Christian movement in SoCal where the rage du jour was Bumper Stickers which had a Crucifix and the saying "I Found It". From my very clever Jewish friends, a competing Bumper Sticker appeared that included a Star of David with the saying "We Never Lost It!" That my friend is two eyes for an eye! 

Well religion aside, "I may have found it", or one of the problems. Like in the whodunits of old --it was not the butler but maybe the power supply feeding the VCO.

In my past posting I mention that the power supply to one section of the VCO was now Suspect #1! In the above schematic we see pin 5/20 where 24 VDC is fed into the Op-Amp that generates the Varactor Control Voltages. The output of this circuit feeds a diode ring with the annotation of various voltages for various frequencies. If 24 VDC is not fed into this Op-Amp, then likely no output. The Voltage at this Pin 5/20 is "0" and of course should be 24 VDC.

The source of the 24 VDC is shown in the schematic below with the output coming from a small on-board DC to DC inverter feeding a diode rectifier and thence on to a three terminal 24 VDC regulator. We have several possible faults on this circuit with possibilities of a non-working inverter and diode rectifier to a blown 24VDC regulator. With absolute certainty there is no voltage on Pin 21/2 (and thus nothing on 5/20).

So, the next step is to solder some wires to the Power Supply Board at the output of the inverter and at the output of the diode ring. (The sense wires are needed because we have no extender boards, and the board itself is not accessible in normal operation.) 

This will provide voltage sense points to determine which of the three possibilities it is. If we see voltage at the input of the 3-terminal regulator, and we know there is no output, so it's the regulator as everything in front of the regulator is good! If we see no input voltage to the diode ring then we know it is the inverter itself, or alternatively no input to the 3-terminal regulator then a possibility of a short in the diode ring which stops the inverter. The sense wires will tell us a lot. There are power supply boards for sale on eBay but kind of spendy. The repair could be something as simple as 75 cent 24 VDC regulator.

A careful reading of the schematic illuminates another test if the DC-to-DC Inverter is working aside from lack of output from the 24 VDC regulator. Hanging off the secondary of the inverter transformer is a winding that would produce a - 5.0 volts at Pin #1 (21/1). If that voltage is present, then you can conclude that the inverter is OK, and the problem is limited to the diode ring or the 24 VDC three-terminal regulator. We are narrowing the set of issues and the likely problem component. 

A thought crossed my mind about a quick test before fixing the power supply which involves disconnecting the wiring to Pin 21/2 and feeding the VCO Pin 5/20 with a regulated 24 VDC. If the radio works, then we nailed the problem and can go about fixing the inverter supply. Regardless, if this is not the main issue it still is an identified problem that requires a repair.

Thing may be looking up and perhaps we found our version of the crotchless panty hose.

In hindsight maybe this check of the 24 VDC should have been done a lot sooner in the process. BUT just think of the fun you and I have had touring the TR-7 and the possible issues impeding the operation of the radio. This is why the root word FUN appears in the word dysFUNctional.

73's

Pete N6QW

Update 1-29-2023: No Star appeared on the horizon nor did a Virgin Birth occur!

Sadly, we are still left with an inoperative TR-7. At times like this I often take a small diversion into the world of Cinema in hopes that my brain operating in the background might come up with some new ideas. That process worked again, but first something about the movie series I am watching on Amazon Prime.

Having made the trip to South Vietnam in early 1965, frequently I like to watch movies about that era to sort of compare what was on the ground to what is being shown on the big screen. The first time I was there we had less than 20,000 "advisors' in country. For those who weren't even born at that time -- that number grew to over 500,000 troops. 

The movie mini-series from Australia is entitled "Vietnam" and there were several revelations in that movie. The very 1st was one of the costars was a very young, flat chested, teenaged Nicole Kidman. She looks a lot better today! Adding 36 years to her body did fill out things a bit. Doing the math --if she was only 15 at the time the movie was made -- she would be 51 today. How cruel that time moves so quickly! [Wikipedia says she is now 55 so about 19 at the time the movie was made. Man for a 19-year-old she had a nice smile if nothing else!]

Oh, the music, some of it covers by others versus the original artists. But the short connection between the teenagers and the loud raucous music that drove their emotions was well done!

The second revelation was the behind-the-scenes premise of the movie (made in 1987) was how Australia got involved in the conflict and how it was not well received by the Australians -- mostly the young people. Sound familiar?

They had the conscription lottery and even scenes showing the taking of ears. The taking of Vietcong ears, after killing them, was like taking the panties of a virgin who was no longer virgin. 

The bivouac area looked much like our camp at Chu Lai. Oh, lest I forget the nightly napalm runs where we would sit in the Officers club, drink in hand and watch the night sky light up was sobering to say the least. I would rate the accuracy as passible although it did appear Kidman was already on the road to an Oscar but some of the dialog a bit hammy. 

So, the brain spit out a couple of messages during the viewing of "Vietnam" and these I will share with you now.

1. Does the receiver work? Only if you inject an appropriate LO frequency in the range 48 to 78 MHz. The normal controls like AF, RF, PBT, Mode Select etc. all work when you inject an external LO.
2. The 4 Boards that control the internal LO may be the general problem area. We have three direct substitute boards (known to be good) and one homebrew Dummy board to replace these 4 suspect boards. Yet the replacements do not resolve the matter. So is this a bad assumption that these 4 Boards are the issue. Or does their replacement suggest there is another piece of rotten wood in the woodpile. 
3. We also theorized that the Digital Control Board may not be receiving the correct BCD code from the Band Switch. We found the BCD Code to be present for all Bands and matched the truth table in the manual. This BCD code sets the range of the two VCOs. The actual VCO ranges as seen by changing the band switch, for the ranges 160-20M is less than 48 MHz and for 15-10M is around 5o MHz. We have VCO change but not in the right ranges and thus no receive. For 160-20M the VCO range should be 49.5 MHz to 63 MHz and for the span of frequencies of 15 to 30 MHz should be 63 to 78 MHz. In short, the Digital Control Board frequency setting is not being "translated" to VCO frequencies. 
4. Various Voltage Levels drive the varactors on the VCO board, and this is what makes them tune the ranges. So does this now place the focus on frequency translation and voltage levels to the varactors. 

We will now look at the varactor supply voltage as a possible issue. You have to get Mary Jo into the back seat of the 57 VW Beetle as a first step. 

It is also sorely realized that without the extender boards you are operating with a hand behind you. 

73's

Pete N6QW

Update 1-28-2023. A Complete Bust!

1. 

My "Grand Plan" did not work! Thusly back to Square One! I completed the Dummy Board, performed a quality check on the wiring and the solder joints and after plugging in the unit and a powering on -- simply stated = NOTHING, No Receive. So that didn't work too well in terms of fixing the problem.

Thus, the next step involved some checks to further ascertain the various existing conditions and here is what I noted:

1. The Biggie = No Change from before!
2. I did look at the 8 input Pins on the Dummy Board connected from the Digital Board and could see as you changed the Norm Aux Switch Positions and changed the Band Switch that the various pins would be either +5 VDC or Zero. 
3. Next, was a look at the output side of the buffers on the Dummy Board and that too went from 0 to 5 VDC again dependent on the settings of the two switches. 
4. To affirm to myself that that backend of the radio was working I pulled the VCO Board and using my external LO injected RF into the Up Convertor and sure enough the radio still receives signals on the various bands I tested. The Band Switch did peak the signals for the Band of Choice. [Hint a possible clue here as I could receive 40M on the band switch set at 7 MHz but also on the 5 MHz setting albeit somewhat weaker.]
5. I replaced the VCO Board and put my DSO Scope/Counter on the Mother Board Pins that transit between the VCO and the Up Convertor. These readings were most interesting as the frequency reading on the 160 - 20M band were in the range of 20 MHz to 48 MHz (The Digital Display read 95 MHz). In normal operation these readings would be in the 49.5 to 63 MHz range as the VCO output is the operating frequency + 48.05 MHz. On the 10/15M Band I saw VCO values of around 50 MHz and the Display read 10 MHz. For this 15 MHz (15 - 30 MHz) of spectrum the VCO should read 63 to 78 MHz. No wonder it is not receiving!
6. Therefore, any analysis of the malady has to account for item #5 wherein the VCO is changing but the digital commands to set the range are off kilter.
7. It has to start with the digital control board and consider that the board may be operating properly BUT may not be receiving the proper information to set VCO ranges in response to the Band Switch positions.

The journey begins with a starting point and now I am focusing on the band switch as that point. The band switch is multi-wafer with one set of wafers switching in the circuitry of the Low Pass Filter and another wafer does the same for the High Pass Filter. These wafers were evaluated as we could see signal increase for a specific band when receiving signals on that band. So, I think the paring of the LPF and HPF are in synchronization which initially caused me to conclude CHECK OFF the Band Switch. I now must conclude that might have been done in haste.

If you check page 2-7 of the TR-7 Service Manual, it states that one of the functions of the Digital Control Board is to acquire BCD data from a wafer on the Band Switch to provide frequency range programming and band control. It also operates with the AUX-7 board to program the proper VCO Range for the bands programmed via the AUX-7.

The BCD data comes from the HPF Module off of the back wafer and is connected to the Digital Control Board pins 1 and 4 on the Mother Board. A Matrix is provided to check the pin state High/Low for the bands. Further processing of this data is done on the Digital Control Board with a BCD to Decimal Decoder IC to produce a 2- 9 Digital Number. 

 

This is the new line of investigation to include observing the state/band on Pins 1-4 on the Digital Control board at the underside of the Mother Board. We are grabbing at the latest straw! 

[I did check Pins 1-4 on the Digital Control Board at the underside Mother Board connector. I got the readings as shown on page 2-7 of the TR-7 Manual. So, that verification of data showed that the proper BCD data is being generated by the Band Switch.] 

It is problems like this one that led to the brilliant invention of the crotchless panty hose or the development of the highly successful marketing campaign to convince the YL's to simply wear no underwear! These type solutions facilitated the journey to the backseat of the 57 VW Beetle. Now we need to find the parallel solutions for the TR-7.

73's

Pete N6QW

 Update 1-27-2023.

1. Yesterday (1/26), I was able to start the initial phases of the board fabrication. Work included making the 3 Pin header to go alongside the 9 Pin Header resulting in a 12 Pin Header, Supergluing the 9 & 12 Pin Headers to the Vector Board as well as the IC Circuit board, Soldering theard Fabrication ICs to the small PC Board, installing the eight 100K resistors and wiring from the two CD4050B's to the 9 Pin Header that mates with the RF Translator Board.

Today will be spent wiring up the 12 Pin Header along with a Quality Check of all of the wiring and connections. I will not power up the board until Saturday. Haste makes waste!

73's

Pete N6QW

Update 1-26-2023. A Root Cause!

I would like to open this posting with a question I posed to chat.openai.com regarding the advantages of homebrew ham gear versus commercially bought radios. Here is the answer.

One advantage of constructing your own ham radio equipment at home is that it can be customized to your specific needs and preferences. You have the freedom to choose the components and design the layout in a way that works best for you. Additionally, building your own equipment can be a rewarding and educational experience, allowing you to gain a deeper understanding of how the equipment works. On the other hand, commercially manufactured radios are generally easier to use and come with a warranty and support from the manufacturer. Commercially manufactured radios are also likely to be more reliable and durable than home-built equipment. Ultimately, the choice between using commercially manufactured radios or building your own equipment will depend on your individual needs and preferences as a ham radio operator.

It also depends on having the "KNACK!" A demonstration of this ability is shown below.

A short diversion, but a sharing of why there is a new blog. In 2021 I designed and built a 7 transistor SSB transceiver with 5 of those transistors being the 2N2222A. The remaining two devices were a 2N2219A (a TO-39 version of the 2N2222A) and the RD06HHF1. 

This project was written up in hackaday and can be found on the N6QW website where it was documented in excruciating detail. An IO group was formed to discuss the project and it died a quick death. The project was called the PSSST (to sort of get your attention) and later dubbed the P3ST. The key to this transceiver design, purposefully did not use EMRFD, TIA circuits, or pieces from Bitx transceivers nor supported by a Facebook group. It was pure and original innovation from N6QW, the hamradiogenius as in this new blog.

Fast forward to late 2022 and the project suddenly spurred some activity on the .io group and that is when several hams protested that the project lacked a complete schematic and no circuit boards or BOM was not available and even further a question of who builds in modules. 

That did it as it was obvious that many of the today's hams simply do not have the intellectual curiosity of our ham founders where you could not buy appliance boxes! In those days one had to make everything! This was the root cause for stopping the N6QW blog.

A friend who has successfully built a P3ST took the next step, and he designed his own circuit board audio amp module using readily available and free software. The final piece was having the boards fabricated in China. This is what homebrewing is all about -- DIY! I am indebted to my friend for having sent this to me. Now look how cool that is.

On dock today is the start of the fabrication of the TR7 Dummy Display board and I will post some photos of that work on tomorrows posting. 

Choices and a hard decision! Yesterday I purchased a FLEX Radio 6400M SDR transceiver. Yes, hard to believe that I would do that! Well, a bit of a stretch here, I spent almost the exact equivalent in dollars to buy a FLEX 6400M to purchase a Inogen Portable Oxygen System for the XYL. 

This Inogen system will give the XYL a better quality of life as it will enable doing more away from home activities. The Inogen is a light weight 6-pound device good for 6 hours away from a home-based large concentrator. With the extra battery it is good for 9 hours and can be charged while in use. The package includes a car charger.

To assuage that very tough decision (new SDR radio for me or portable Oxygen system for the XYL) I have designed a small metal nameplate which I will cut on my CNC Mill that says FLEX 6400M. This name plate will be installed on a prominent location on the Inogen. So, now every time I look at the XYL I will think FLEX 6400M. 

Is this a Hobson's choice as we have to keep the old girl breathing. But in fact, the 6400M would not frequently say "you are doing it wrong"!

73's

Pete N6QW

Update 1-25-2023. Rookie Mistake.

I have had the TR-7 for a month now and have made some progress on the resurrection. In review, I have concluded the lack of receive is an issue with the Digital Display Board and it is possible to bypass that board by fabricating a Dummy Display Board. I am on that journey.

I got sidetracked as the specified IC's only come in the SOIC version which then required some SOIC Carrier Boards which are stuck in a snowstorm. An alternative plan was to try and find the PDIP version of the IC's which are obsolete. On one site today there was a mention of a substitute part, the CD4050B. Boom! I have a bin of those in the PDIP form factor!

Some quick work with G-Simple and 10 minutes on the CNC Mill, I now have a circuit board for the CD4050's. Rookie Mistake in the failure to check for substitute parts. I could have had this built a week ago!

I also spent some time today creating "wire lists" for the Board Connector Sockets to the Dummy Board Pins and these are show below,

Am waiting for some Superglue to be delivered tomorrow and then I can finish the mechanical fabrication and thence onto the electrical wiring.

A giant progress day! Getting excited!

I now have a lot of extra parts for the bins. Taking one's time avoids Rookie Mistakes and wasting resources (Read $$$)!

73's

Pete N6QW

Update 1-24-2023. Initial Fabrication of the Dummy Board.

Above is the initial "Fit Check" of my homebrew Bare Display Dummy Board. The final size of the board was 2 Inches by 3.5 inches. As usual the spacing between the pins on the TR-7 boards was not exactly the spacing of holes in the Vector Board. Thus, I had to drill a row of holes between the normally spaced holes on the Vector Board. I just plain got lucky with the drilling project! Although this would not have been possible without the use of my manual Milling Machine operated as a Drill Press.

Next are some photos of the new row of holes and the fitting of the header into the holes. I have not fabricated the three-pin header and thus you see some holes without header pins.

Yes, this task requires a certain amount of "knack".

I love it when a plan comes together!

Pete N6QW

Update 1-23-2023. Where is Rex? (Found Rex and he lives in Maine and right now snowed in -- shipment in a day or two)

Last week I placed an order with W1REX for the SOIC carrier boards and got a confirmation my PayPal account was hit for $11 (yes, a bit of robbery here). Suddenly a black hole with no order acknowledgement nor shipping info. What I bought would fit in a small, padded pouch.  (BTW his website is clear all you get is the PayPal affirmation and if you want shipping info you have to email him which I did.)

So, the task for today -- Find Rex! But now I had time on my hands and so it is the work of the devil that jumps into the fray with nothing in the workspace. 

I turned to chat.openai.com and made an inquiry. For those of you with culinary skills that are limited to boiling water, I made an inquiry about what could I cook based on a limited list of ingredients one might find in their refrigerator. I was pleasantly surprised at the answer and was not dissed such as the time I asked the AI which country had the best-looking women under 30? 

 My inquiry:

I have the following ingredients in my refrigerator what kind of meals can I make. Milk, wheat bread, eggs, sharp cheese, sliced pepperoni, butter. cream cheese, green olives?

 

With those ingredients, you could make a few different types of meals:

1.       Breakfast: French toast or a breakfast sandwich with scrambled eggs, cheese, and pepperoni.

2.       Lunch: Grilled cheese sandwich with pepperoni and olives or a pepperoni and olive cream cheese spread on wheat bread

3.       Dinner: Egg, pepperoni, and olive casserole or a quiche with a wheat bread crust.

Keep in mind that these are just a few suggestions, and you could also get creative and come up with your own unique dish.

 

Then I thought of the BTE's who could actually use this application to learn about the technical side of amateur radio despite having an Amateur Extra ticket garnered by memorizing the answers to a few questions.

Before my GI Bill ran out and having successfully used it for graduate studies, I was able to use it to cover a Real Estate licensing course. The course instructor was quite honest when he opened the 1st session by saying we are not here to teach you about real estate -- we are here to teach you to pass the state licensing examination. 

There were 2000 questions in the test pool and so after each testing session, class members would attend a party where the entry fee was to supply two questions from the test. The trick was these questions would not be used on the next test and so the subsequent question pool was now less than 2000 and when you got ready for the test -- you were told in advance these are not on the next test. I guess someone at the ARRL has a real estate license from my state.

Find Rex!

73's

Pete N6QW

Update 1-22-2023. The Drake Dummy Digital Display Board.

SCE (our electric service provider) has signs all over the place about calling them before you start digging around your home. In fact, there is a number similar to 911 you can call that will tell you about the gas and water lines too that may be present! 

So, following that concept, I thought I had better look at the official Drake Dummy Display Board to see if there are any landmines in the mix. We found a photo of the Dummy board and it was very telling.

1. The photo is of the underside of the Board, and we immediately spot the 9 Pin and 12 Pin Connectors. We can see the outlines of the MC14050B IC's and eight connections to through hole components which most likely are the 100K resistors. 
2. A large ground plane is evident and there must also be circuitry on top side of the board which connects to the pins. Thus, we have a double-sided board. There is at least one more component to be installed and that is a bypass cap connected between ground and the 5 Volt Rail.
3. Drake used a unique homebrewed tool to remove the circuit boards from the cage assembly. The tool is a "U" shaped device made from a coat hanger. There are holes in the circuit boards that mated with the tool to "carefully lift" the boards from the mother board connector. Note the two holes in the Dummy Board. One of those holes is used to pass a coax from the Up Converter Board to the High Pass Filter Board and there is a similar hole on the regular Digital Display Board. The second hole is so you can insert one end of the tool into the board and remove the Dummy Board
4. Now at a Critical Juncture. The 12 Pin side goes to the Digital Control Board and the 9 Pin side goes to the Translator Board. We also have the schematic and  there is a huge "get in your shorts" issue (and it is not Mary Jo) with the proper wiring from the pins as any underside wiring may be reversed from what you see on the schematic. Example: Take the standard octal tube socket. Pin #1 is counted from the bottom view as the pin to the right of the slot. If you counted from the top side of the socket using that same template what you may think is Pin 1 is actually in Pin 8. Thus, I will need to study the two boards and their schematics to verify the pins. Luckily, I have two spare boards and can check this out. This is the measure 40 times and cut once type of challenge.
5. Another bit of a clue from the underside is "the how" the Drake Board was laid out.

As I await to hear from W1REX regarding shipment of the carrier boards, I have some very critical evaluations I must conduct.

The 1st bit of good news is that Drake has numbered the Pins on the Digital Board. See the photo from the TR-7 manual below.

Note in the lower right-hand corner of the board the lower number 41 going to the higher number 52. This is the 12 Pin Connector so that the edge pin is #41 going toward the center of the board to Pin #52. These are the order of the Pins and the wiring to those pins as shown from the top of the dummy board but reversed on the underside. However, take a closer look as the 1st pin shown in the wiring schematic is Pin 42 and none of the Pins are numbered in order so lots of crossed wiring. Careful in what you do! That said the wiring to the RF Translator Board has the pins on the Dummy Board in sequential order 41- 49. Close attention gang!

The RF Translation Board has the same markings for the Pins that match the schematic and are in order so no cross over wiring.

Watch this space.

Pete N6QW

Update 1-20-2023. Parts are Here! Well almost.

A banner day yesterday, as a pouch from Digi-key arrived in my mailbox. Here is a shot of some of the stuff in the bag.

Of note is the 0.156-inch pitch on the Perforated Board (Vector Board) and the Header strips. The plastic tube contains 10 of the MC14050B noninverting buffers and are small. So now a task list of what needs to be done.

1. The first realization is the 16 Pin SOIC ICs would need some design effort on my part to create a CNC Milling program -- time I don't have as the width is 0.65mm. Then, I thought of Rex Harper W1REX who sells a version of MePads which are carrier boards designed to take the SOIC footprint. Those had to be ordered. That is the well almost part of the heading. 
2. The Vector Board is plain board without any pads/per hole and so the Headers will be super-glued to the vector board. On one end are 12 pins and on the other are 9 pins. The headers out of the box are 9 pins and thus I need to cut up one header to produce a three-pin header. With a 0.156-inch spacing, pretty easy to do.
3. Since all connections will be done with the Pins into the TR-7 Board Sockets, I can pretty much arrange the actual circuitry for the best fit. That said the W1REX pads will drive some of that layout. 
4. The mode of wiring will be wire wrapping and thus I need to check my stock of wire-wrap material and find the wrapping tools. This is digital and OK. I do plan to solder to the short side of the header pins as this will anchor the headers strips in addition to the superglue.
5. While awaiting the W1REX pads I can make some progress by sizing the Vector Board (3X6 as bought) to the actual size needed to span the two boards inside the TR-7. I will also have to pay attention to any insulation needed on my homebrew Dummy Board since there will be underside wiring that could ground to the board cage metal assembly. Again, just like the interactions with Mary Jo, you got to think ahead with the use of protection from any unintended consequences. 

While I was hoping for a "quickie" one and done event, this will add about another week of agony. My intent is to try and share construction photos as I fabricate the Display Dummy Board.

73's

Pete N6QW

Update 1-19-2023. Thank You Italy!

As hams we must thank Marconi for planting the seeds of our hobby, but we also must say Thank You Italy for producing some really top-drawer hardware. One person comes to mind who recently became a SK at 95. RIP Gina!

I was first licensed in 1959 at age 17 and it was a struggle between Ham Radio and FB art forms like above. Mary Jo didn't look anything like this and had a few extra pounds but still had a superb personality! (Yea right!)

It is with regret that I must report that the parts from Digi-Key did not arrive in yesterdays' mail. Hopefully today as I suspect Monday being a holiday messed up the delivery. 

It is with hope that some blog readers did indeed test drive the chat.openai.com Already I have had some comments like well it doesn't do this, and it doesn't do that. Likely true -- but this app is only about three months old and is still learning and in time the accuracy will improve. If you are a golfer, you certainly didn't play like Tiger Woods within a month or two after you started playing. So, get a grip. 

Several hams have asked the application to "design me a radio". The answer back did not satisfy their expectations. The issue is very like the old saying regarding early computer systems: Garbage in and Garbage out!

A starting place is to inquire about the element blocks of a radio system. Once those blocks are identified, then you can inquire about what are the best approaches for say the LO block, then repeat that process for say the Mixer stage and so on. Finally, you have identified the "best approach" for each of the blocks wherein YOU pick and choose the final configuration elements. 

The AI has facilitated the design of the radio -- but the man in the loop makes the final choices that considers things such as ease of construction and replication, the size, weight and cost. The AI makes the design process as such where a design team of one could produce a ham rig versus literally a cast of thousands that would have to do the research and evaluation without such a tool.

We all have prejudices. Those often color our approach and embracement of new technologies and processes. I have a prejudice against analog VFO's as I think they are akin to doing brain surgery with a rusty spoon. I freely admit that. But I want so much more from the radios I design and the leading element in the determination and capability is a Digital LO. Cost is no longer an issue as the Digital LO can be built in direct cost competition with a conventional LC Oscillator. Stability, frequency repeatability, and the availability of cool displays simply are built into the Digital LO scheme. These are the Achilles heel of LC VFO's 

I will not leave you hanging so here is a question I asked and the response from the application. My question involved which is better DDS or PLL when you consider several factors. [Stability, Cost, Repeatability, Drift, and the all-important Phase Noise]

Both DDS (Direct Digital Synthesis) and PLL (Phase-Locked Loop) approaches have their own advantages and disadvantages when it comes to cost, stability, phase noise, drift, and frequency repeatability in the design of a digital local oscillator (LO) in a radio system.

DDS typically has a lower cost, better frequency repeatability and flexibility, and lower phase noise compared to PLL. However, DDS has a higher drift and is less stable.

PLL, on the other hand, has better stability and lower drift compared to DDS. However, PLL has a higher cost, worse frequency repeatability and flexibility, and higher phase noise.

Therefore, the best choice between the two approaches depends on the specific requirements of the radio system. For instance, if stability and low drift are the most important factors, a PLL-based LO would be the better choice. If cost, frequency repeatability, and low phase noise are the most important factors, a DDS-based LO would be the better choice.

So, the AI has now afforded us a criterion to decide which is the best approach for our application. [Is it the 200-pound FUN Blonde or the 120-pound, 29A bookish Red Head? It depends!]

The AI application assists us in making various selections for the elements that comprise the Digital LO. At this stage you cannot simply say design a Digital LO but likely in time you will be able to do that, but not today.

Late edition. I asked about the history of Amateur Radio in the USA and the role played by the US Navy. See the response. Two names showed up which are unknown to me.

Amateur radio, also known as ham radio, has a rich history in the United States dating back to the early 20th century. One of the key figures in the early development of the hobby was Hiram Percy Maxim, who founded the American Radio Relay League (ARRL) in 1914. The ARRL, which is still in operation today, is the primary organization for amateur radio enthusiasts in the United States.

Another important figure in the history of amateur radio in the United States is Lieutenant Commander Kenneth Norton and Charles D. Park, Jr. of the US Navy. These two individuals played a key role in the development of high frequency (HF) radio technology, which greatly expanded the capabilities of amateur radio operators. They also established the first regular schedule of amateur radio communications between the United States and Europe in the 1920s.

The US Navy has also played a significant role in the history of amateur radio in the United States. Many navy personnel have been amateur radio operators, and the navy has supported the hobby by providing equipment and training to sailors. The navy has also sponsored several high-profile amateur radio events, such as the Naval Radio Amateur Civil Emergency Service (RACES) and the Navy-Marine Corps MARS (Military Affiliate Radio System) programs. These programs have helped to promote amateur radio and provided valuable communications support during times of emergency.

73's

Pete N6QW

Update 1-18-2023. Parts are due in Today.

In the interim I asked chat.openai.com about matching transformers that we use so much in our homebrew rigs. The classical matching of a 50 Ohm to 800-Ohm transformation was chosen for evaluation. (Like in a match to W7ZOI's 9 MHz Crystal Filter paper of 2022).

But you do have to know some stuff ahead of what you ask, and my question was about the match, and I specified the one winding was 4 Turns. The match as the AI correctly gave was 16:1 -- BUT you have to know that the match is based on Turns ratio Squared! So, I must square the 4 to get 16 and then the other side must be 16 times that or 256. 256/16 = 16 to 1. Thus, the second winding is 16 Turns. A check 16^2 = 256 and 4^2 = 16 so 256/16 = 16 to 1.

The turns ratio for matching a 50 Ohm load to an 800 Ohm load using a ferrite core transformer with one winding being 4 Turns is 16:1.

A Word of Caution as some answers you get requiring computational analysis may be wrong. Caveat Emptor. I asked how many dBm is 1000 milliwatts and here is the answer. [You can check it.]

1000 milliwatts is equal to 30 dBm

Google most likely would call up a convertor app versus giving you the answer.

Here is another example: I asked to solve the equation X^2 - 1 = 0

The equation X^2 - 1 = 0 can be solved by adding 1 to both sides of the equation to get X^2 = 1. To find the solutions of the equation, we can take the square root of both sides, which gives X = sqrt(1) or X = -sqrt(1) and the solutions are X = 1 or X = -1.

Google would only refer you to a calculator. You can see the power of the AI.

73's

Pete N6QW

Updated 1-17-2023. Look Ma, Artificial Intelligence (AI), lands at the N6QW Shack!

Still awaiting the Parts for the Display Dummy Board, but the good news is my #1 son is visiting whose day job is a Software Architect. He introduced me to chat.opeanai.com.

With this amazing AI tool, you can write Arduino Sketches by simply describing what you want to do. 

I should mention my first encounter with microcontrollers was with the PIC 16F84 back in 2001. I could not find an Amperite 3 Minute Time Delay Relay (TDR) for use with a 3CX800A7 amplifier I was building. That is when I thought about using the microcontroller as a TDR. It worked!

So now some 22 years later I simply wrote some text about what I wanted and out spits the code for a TDR using the Arduino Nano -- All Done with AI.

Basically, I said I have an input and when that input goes LOW an output goes HIGH and essentially remains there after a 3-minute Time Delay. I then added if another, separate input goes low then the output goes low. This is the code from the AI.

No hand driving here as this is what came from the AI. I have not loaded it onto an actual Arduino, but it sort of looks Kosher! The loop within the loop looks to see if Input 2 is LOW which would open the output on Pin 7. 

In my mind Input #1 is a momentary Push Button not a continuous closure. The same is true for Input #2. So that may need a twizzle to insure jut a momentary engagement is all that is required.

Just poking about this evening, I asked the AI to design a Band Pass Filter centered on 14.2 MHz with a 400 kHz BW. See the text response below. [BTW this is how it is done in the Drake TR-7.] 

Caveat -- the 14.2 + (400kHz/2) = 14.4 MHz, and the 14.2 - (400kHz/2) = 14.0 MHz. I don't know how the AI got 14.3 and 14.1 MHz. The Zin/out has to match and they are combined in parallel not series. This answer while a cool response likely needs a bit more vetting.

A band-pass filter centered on 14.2 MHz with a 400 kHz bandwidth can be designed using a parallel combination of a low-pass filter and a high-pass filter.

First, design a low-pass filter with a cutoff frequency of 14.2 MHz + (400 kHz / 2) = 14.3 MHz. This can be done using a Butterworth or Chebyshev filter design with a desired number of poles.

Next, design a high-pass filter with a cutoff frequency of 14.2 MHz - (400 kHz / 2) = 14.1 MHz. This can also be done using a Butterworth or Chebyshev filter design with a desired number of poles.

Finally, combine the low-pass and high-pass filters in parallel, ensuring that the impedance levels match. This will result in a band-pass filter with a center frequency of 14.2 MHz and a bandwidth of 400 kHz.

The AI part takes some learning on my part and how to command the instructions. But this is exciting and a whole new bag of tricks for the greater ham community. Heck this is just like getting an Amateur Extra Ticket today -- you don't have to know anything yet can write Arduino sketches or as the case may have full ham privileges without even knowing how to turn on a ham rig!

 

This is the Golden Era of Ham Radio.

Pete N6QW

Update 1-15-2023. Temporary lull while awaiting the parts for the Display Dummy Board.

That said a couple of radio related links that are a must see.

The first is from Todd, K7TFC and his Mostly DIY RF website where he is offering some amazing modules such as one coming out in February, an I2C Rotary Encoder Module. 

Another is a Dual Gate MOSFET (SMD) installed on a carrier board. Now you can build some of my older projects that featured DGM's. 

Also available is a complete board for the famous W7ZOI HYCAS IF Module. Best of all a source for Crystal Filters (Multipole QER) sold as parts, pieces or a completed assembly. These come in four different frequencies.

Mostly DIY RF

A bonus is a recently published newsletter from Todd and an announcement that his wares are sold both on eBay and Tindie, which is the second link.

Tinde

Tindie is a website where "Makers" can sell their various wares. Some of the stuff is really retro like building your very own Z80 computer or control a laser (where hopefully Ralphie doesn't shoot his eye out). Other neat stuff is a case for an Arduino Uno which unmounted and stand alone is a kluge! 

Also of fashion is ladies' electronic jewelry such as small LED lit earrings in the form of Christmas trees. Another is a space charged (capacitor) pair of earrings. 

That offering indeed leaves me scratching my head. The key is that many of the modules are readily available as embeds in your next project.

I will continue to post to the blog but not much on the TR-7 Resurrection until I get the Dummy Display parts on board and built. [This is like the agony of awaiting to see if the girlfriend's pregnancy test is positive.]

Updated 1-14-2023. The DR-7 Dummy Board.

Our troubleshooting adventures have led us to now focus on the DR-7 Digital Display Board. Actually, that is a misnomer in that the board has many more functions that just displaying the operating frequency. It is the portion not associated with just a "frequency counter" function that is awry.

We have some important evidence to support that point in that the counter in the General-Purpose mode operates FB. The 2nd point is that a board swap of the VCO, Digital Control and Frequency Translator Boards did not change anything.  The third point is that we can make the radio receive by pulling the VCO Board and introducing an LO signal into the Up Convertor Board. The final piece of evidence is that I removed the Aux7 Board and the same issue.

If it walks like a duck, looks like a duck, talks like a duck then it is not an elephant!

So, the next step as suggested by Drake is to completely bypass the DR7 using the Dummy Board (see the TR-7 Manual starting a 2-70) which I will have to fabricate and shown in the above schematic. 

Essentially this dummy board is some 100K resistors and two inverter IC's. The parts are all available at Digi-Key. There was a bit of "engineering" involved as the plug-in headers are 0.156-inch pitch and the perforated board used as the base is also 0.156-pitch. 

The ICs are cheap enough but only come in SMD. I may need to make some SMD adapter boards on my CNC. I ordered enough to make several boards as I see a 1st prototype and then a final board. Likely I will wire wrap the connections (this is digital so OK). It may not be pretty but avoids the use of that nasty ferric chloride crap.

I also hope with the extra 0.156-inch header pins I purchased to start building some prototype extender boards -- again more CNC work.

Speaking of CNC Mills. I see some bargains can be had for CHEAP from our friend Jeff Bezos. I saw this and it is at an astonishing price and likely you would need to spend more to get one fully operational but 62 people gave it a 4.3 rating out of 5. I would never suggest you buy this specific unit -- but only to show that prices are way down. Think more of something in the range of $300 total to enable making circuit boards. See also:

 http://www.n6qw.com/CNCMILL.html

Drake was clear, likely thinking ahead to hams who homebrew stuff and would build a Dummy board, that the pins do not simply wire across. One side has 12 Pins, and the other has 9 Pins.

 

Updated 1-13-2023. Friday the 13th! The roads led back to Rome. 

After a lot of false trails (and trials) we found the road leading back to the Digital Read Out Board. Think for a moment that on 5 bands the same digits appear in the display and on two bands the same (different digits from the 5) appear on the display. We also know that for two bands (15/10) that the loaded data into the synthesizer correlates to the VCO and the magic 48.05 IF Frequency. Finally, as a General-Purpose Counter the DR7 works with a large Caveat from Drake that the Digital Counter portion could work FB, but the rest does not!

Several controls do not operate on the 10/15 bands (which presumptively is sort of working albeit with the wrong loaded frequency). The Up / Down frequency buttons which adds/subtracts 500 kHz and the Fixed Receive VCO test do not work. 

Shown above is a partial schematic of circuitry located on the DR7 board. Along the left side are shown inputs from the Up / Down switches, the AuX7 Board and the Band Switch.

In the tests where I bypassed the VCO, the Band Switch does seem to peak up on the bands correlated to the band you want. I did test the receive on 80, 60, 40 and 30 Meters. So, at this point I think the band switch is switching in the right band. BUT there is a 4-pin matrix that needs to be checked to see if the band switch is actually generating the BCD code for each band. [Also, on the test list.]

Several pieces of Critical Information! Initially I discovered that Aux7 Board was installed backwards in the card cage. Could something be smoked on that board that is causing a false input to U9002. I suspect that since the Aux7 board is an accessory and no mention of a dummy replacement board it can simply be removed. [On the test list.]

U9001, U9002 and U9003 are interconnected and something amiss there could impact the outputs from U9005 and U9006. With the exception of U9003 replacement components can be found. U9003 is a Programmable Read Only Memory and that might be a tough nut to crack in terms of finding a replacement.

A lot of the circuitry on the DR7 is protective in nature like to prevent damage to the display itself and to prevent an operation where you have a frequency range being used different from the Low Pass Filter range. It is a complex piece of circuitry.

The Drake TR-7 Manual states when you are at this point that you should install the Dummy board that bypasses the DR7. Several blog readers sent along the schematic for the dummy board and so that likely will be the next task. 

Free Hubcaps and for another $200K you can find the rest of the parts for a 1940 Cadillac de Ville restoration. The final result is a rather nice 83-year-old car that can't pass the California Smog Test!

73's

Pete N6QW

Updated 1-12-2023. A Reset. When you are up to your butt in alligators, it is hard to remember the objective was to drain the swamp.

[Late Breaking Data: I reinstalled the VCO and noted that the Display still read 95 MHz on the bands 160-20M and 9.9 MHz on the bands 15/10M. The VCO checks per Section 3 did not produce the up counting to either 17MHz or 32 MHz. I next looked at the value of the signal from the VCO to the Up Counter which actually should range from 48 to 78 MHz for normal operation.

1. For the 160M to 20M bands then VCO value was 45 MHz which like would screw up the math logic since the least number would be 48 MHz.
2. For the 15/10M bands the number is 57+MHz which then would show as something less than 10 MHz --- and it does.

This now causes a bit more to ponder as it appears with a 57+ MHz LO does decode as close to 10 MHz. 

The problem may involve the Band Switch and the Digital Control Board along with the Frequency Translator. Frustrating is the operative word.]

Thusly, the radio can operate on receive if you bypass many of the critical Circuit Boards that make it operate in a normal fashion. The task now becomes to look at those 4 boards and attempt to narrow the size of the anomaly. [The Four Boards: VCO, Digitial Control, RF Translator and Digital Display Board]

A reminder that three of the four boards are replacements that supposedly are working. Yet with new boards the anomaly presents the same two conditions. A correct frequency display and the radio does not tune on air stations. 

Section 3 of the TR7 Manual provides test and alignment information. Starting with the 1st board ahead of the Up Convertor, The VCO alignment and test provides a way to test the individual VCO's. 

For the lower frequency VCO place the Band Switch on 2o M, the AUX on Normal and then pressing the Fixed Receive button. The Display should count up from 14 MHz to 17 MHz and this tests the lower VCO. For the higher frequency VCO you repeat the same only the band switch is on 21 MHz and the display should count up to 32 MHz. 

Drake outlines an alternative procedure to check this in the event the DR7 is not installed. I am hoping to use this alternative procedure in the event the DR7 board is toast. An earlier quick test did not show the Digital Display counting up for either band switch position.

This is the starting point for the next round of "My Adventures with the Resurrection of the Drake TR-7".

Updated 1-11-2023. Significant Progress.

Today I did what I suggested in yesterday's post. I removed the VCO board from the Card Cage and into the port on the Up Convertor marked for the LO (VCO) I injected a signal that was a sum of the desired operating frequency plus 48.05 MHz. 

The two videos below show that I could receive a net on 7.255 MHz (48.05 + 7.255 = 55.305 MHz). I also cruised down to WWV on 5 MHz and up to WWV on 10 MHz.

The tests in these videos confirm with a LO of the proper frequency (plus having the band switch in the proper range) the TR-7 receives signals. Since the VCO board was absent, we had no frequency display. 

But what also is confirmed is that there is something amiss with one, several or all four boards. I now have added the DR7 Display board to the pile. That seems a remote possibility but is in the suspect's list if only for further evaluation and ruling out of the mix.

Additional important confirmations include that the input signal has a route through the Antenna Connector through the LPF, HPF and Antenna TR relay to the Up Convertor Board. Check off any concerns about an open circuit in the receive signal path. 

The significant conclusion is twofold in that the generation of the LO signal to the Up Convertor Board is awry and most likely there is a secondary issue with regard to the signal source being supplied to the Digital Counter. These could be the same problem or two separate problems.

It was a good day. I am encouraged as I was also able to function many of the receiver controls. A long road ahead, but the TR-7 is inhaling RF. We now have narrowed the problem search which initially was on a global scale now down to something the size of the State of Texas.

Curious thought about Raytheon and FLEX Radio as they jointly modify the COTS FLEX 6000 Series SDR Radio for use as the primary communications system for the US Air Force? Howzitgoin guys? 

I might like to suggest that the TR-7 was the FLEX 6000 of about 50 years ago.

[COTS = Commercial Off The Shelf for the BTE's.]

Pete N6QW

Updated 1-10-2023 Blinded by the Light (Manfred Mann). It never rains in Southern California!

Blinded By the Light...

Yesterday, the two TR-7 replacement boards arrived (Digital Control Board and the RF Translator board) which were promptly dispatched inside the radio. Powering up the radio we find nothing has changed as the same problem exits. Simply following the Drake Malfunction Process of Board Replacement did not resolve the problem. BUMMER (in Caps)!

So, the fault analysis, is laid back on my shoulders as perhaps lacking in full exploration of the possibilities. My noodling caused me to think a bit about what I am observing with an eye toward a final resolution. 

Once again, the process goes back to what do we know and/or observed and did any of the changes made make any impact.

1. The same two display readings, post board swapping, persist in concert with the band change indication.
2. A new branch thought process leads to two conclusions with one being a display of frequencies that are aberrant. The good news is a change of the display linked to the upper and lower VCO circuits BUT not correct. The frequency displayed is a result of a complex process routed in digital logic. A chart in section 1.3 shows the VCO frequency being sent to the Display Board and from there that numeric is mixed with other frequency inputs to show the actual operating frequency. In short, a 63 MHz VCO is magically translated to a 14 MHz readout. A numeric called N is derived from the Band Switch (BCD) position and that is also used in the display readout calculations. Complex is a good word! So, problem #1 is the readout logic is awry
3. The aside problem (#2) is that the conversion process is amiss as nothing is being received off air. If the two problems were unrelated, then you could be hearing band activity without the frequencies being displayed properly. In fact, on one page of the TR-7 manual Drake mentions that the General-Purpose Frequency Counter could be working but the display is not. This gives rise to having the counter work properly but not the display.
4. But since we have the two-problem condition they have to be linked. Early TR-7's that were sold had a jumper board so that the unit could be purchased without the Digital Display and the radio would operate. Certainly, temporarily bypassing the Digital Display would remove that as an issue and then we could focus on getting the radio part to work. I need to research what is that display jumper board. A similar situation exits with the Noise Blanker if that feature is not installed, then in its place is a "dummy" board. Both jumper boards likely have active electronics and not simply a wire bussing of pins.
5. Since three replacement boards have been installed (VCO, Digital Control and RF Translator) and nothing has changed then we have failed to find the malfunctioning circuit/module. More noodling time required.
6. The RF conversion process leads us to the Up Converter board. This board is on the critical path insofar as hearing on air signals. There are two main inputs to the Up Convertor board, and they are the LO (VCO) and the input from the High Pass Filter (HPF) Board. The HPF has a coax output which actually has three components riding on that coax, comprised of on the air signals, the 25 kHz calibrate signal and the VLF input. 
7. The VCO in turn receives signals from the RF Translator board and the Digital Control Board. A possible test to run. Pull the VCO board and inject a 48-78 MHz signal into the Up Convertor from a Si-5351 and then see if we can receive on air signals. This has several test possibilities in that if this works, then we have bypassed the three new boards. If we still do not receive, then the Mixer (DBM) in the Up Convertor is at issue (or the LPF).

Pete N6QW

1. [A Preface: The intent of this blog is the construction of homebrew radio equipment. This troubleshooting exercise is not out of step with that intent. Our homebrew radios have advanced to something beyond an 8-part Michigan Mighty Mite or a simple Crystal Shere et. Many of my current projects have microcontrollers and/or single board computers embedded within the architecture. Thus, the problem solving and troubleshooting process is no different for the TR-7 or a Homebrew SDR Transceiver.] 

Updated 1-9-2032. More Tests that show frequencies are not being loaded into the synthesizer.

This TR-7 troubleshooting process is like a game of Whack A Mole. Something new keeps popping up for evaluation. The path however leads back to the Digital Control Board (DCB) as a starting place. A replacement board will be here on Wednesday.

The analysis so far is that frequencies are not being loaded into the frequency synthesizer. This test procedure revealed that the frequency synthesizer was drifting down, a sign it was not locked. Part of the frequency locking involves a phase detector in sync with a 500 kHz signal from the Pass Band Tuning Board. We know that signal is being generated.

The test in the video involves injecting a frequency from the RF Generator and as the frequency drifts downward that frequency is detected by the TR-7. This shows that in part that the TR-7 is working and highlights where it is not!

It is like finding a set of 1940 Cadillac hubcaps (NIB) at a garage sale for FREE. For another $200K you can find the rest of the parts to completely build a 1940 Cadillac. When done it is still a car that is 83 years old.

Updated 1-8-2023. More Analysis on the signal path of the TR-7. [UPDATED]

While I am doing some things my time is still limited. I did not try as yet to inject as signal into the bands that appear to be working. Maybe today. But that also gives rise to where you inject the signal.

First some observations from the block diagram below. [From the Drake TR-7 Manual.]

The Up Convertor board has 3 inputs including the normal RF coming from the antenna, but also the VLF input and a 25 kHz signal off of the Pass Band Tuning Board. The Calibrate signal is not a normal crystal calibrate signal as such, but a 500 kHz reference signal that is divided by 20 to yield a 25 kHz signal. So, the calibrate signal is injected downstream from the antenna. Another Ah Ha moment is that you physically have to jumper two ports on the rear apron marked external receiver and external antenna. The   jumper completes the signal path from the antenna to the receiver circuitry. That jumper is in place.

So, some things to ponder why no on-air signals are heard (aside from the LO generation issue) as there could be an open somewhere ahead of the Up Convertor. So, for testing for signals on a specific band the ideal would be to inject a signal just ahead of the Up Convertor board and then to work your way back through the HPF and LPF to the antenna port. There is a TR relay in the loop as well so that is another potential “open” opportunity ahead of the Up Convertor.

Now if the calibrate signal is engaged and inputted to the Up Convertor and the LO signal coming from the upper VCO is valid but not synchronized with the band switch (BCD code) then a calibrate signal will pass through the Up Convertor and be detected, while you may not hear on air signals for that band. Another clue. If the Lower VCO is not working, then likely you will not hear the calibrate signal. That is indeed the observation.

Keep in mind that the Up Convertor is nothing but a 2N3866 RF Amp, a 30 MHz LPF and a Double Balanced Mixer. If it is working for the 10/15 Meter Bands, then the whole board is good.

 

Bottom line for additional testing: Place the rig on 10 or 15 Meters and inject a test signal for either band into the Up Convertor and see if it can be heard. Then, once found (if found) move the test signal to the HPF and then to the coax connector. This action will test any open circuits in the HPF, LPF, TR relay. 

If the Digital Control Board is awry, then while it is apparent that 10 or 15 Meters may be working – that may not be the actual received frequency range. This may require running the RF Signal Generator in the 15 to 30 MHz range to find the actual received band. That will provide additional data and corroboration of any issues with the Digital Control Board.

Each time I noodle through the block and circuit diagrams I marvel and certainly get a feel of the extensive engineering analysis and design that went into the TR-7. Urban legends have it that Drake took several years to develop the TR-7. Just think if Drake had tools and technology that exist today and how that would have impacted the overall design.

I have heard several hams who commented that the TR-7 was superior to the Collins KWM-380. I have not looked at the KWM-380 but there indeed may be some truth in that posit.

Update to the Update: An eagle-eyed blog reader emailed me that the block diagram and the Up Convertor appear in conflict. Actually, they are not as the VLF Antenna and the 25 kHz Calibrate signal are connected to the High Pass Filter (HPF) board just behind the S Meter. 

Thus, only a single coax cable goes from the HPF and that is shown as the lower input on the Up Convertor schematic. I would proffer that this comment is based on the schematic for the Up Convertor has shown two inputs (LO and the signal from the HPF) where one might expect to see four inputs (LO, Signal, VLF and 25 kHz). Likely, this was a practical solution to a fabrication problem. 

The Up Convertor plugs into a card slot in a card cage assembly. Getting one connection onto that board (from the HPF) is hard -- now try it with three. Thus, bussing the three connections on the HPF board eases the fabrication process.

73’s

Pete N6QW

Updated 1-7-2023. New VCO Board.

The replacement VCO Board arrived yesterday and was installed in the TR-7. It did not fix the display issue or make the radio receive on air signals. However, it did make the radio tune the Crystal Calibrator signals on 10 and 15 Meters which is new. 

The 10- and 15-Meter bands are linked to the higher frequency VCO. On the lower bands however you hear nothing, but garbage and these bands are controlled by the lower frequency range VCO. Ultimately the setting of the VCO's starts with the Digital Control Board (DCB) and the Frequency Translator Board. So, it is best to start with DCB and then move to the Frequency Translator Board. I have two replacement boards coming but they will not be here until next week. This follows Drake's malfunction process -- find a problem and replace a board!

There is a distinct path from the Band Switch which provides a BCD signal to the two boards (DCB and Translator) which operate in such a way as to decode the BCD and create voltage levels to set the VCO and VCO range along with mixing the PTO signal. This process finally creates a LO Signal in the range of 48.05 to 78.05 MHz.

The DCB has an additional function and that is to accept signals from the AUX-7 board that turns the TR-7 from a Ham Band Transceiver to one which will work on any 500 kHz segment in the range of 1 to 30 MHz.

I got the radio free and for a small fortune can make it work like a high-end radio of 50 years ago. I love the somewhat distorted logic!

Some critical comments about the trouble shooting process. Basically, it involves a lot of noodling and a reasoned approach. It also requires understanding what you are observing. The fact that I can hear the crystal calibrator on the two higher bands (higher VCO) is telling that the VCO is being controlled and responds with the PTO (main tuning knob). But the fact that you aren't hearing normal signals suggests that the higher VCO is out of sync and maybe out of lock with main band switch. 

We see two sets of numbers being displayed on the display which we have tested as a general-purpose counter. For the lower range VCO the display reads 95 MHz for all bands between 160 and 20M. For the higher range VCO it reads 10 MHz for the 10/15M Bands. Keep in mind the output of the VCO board feeds the display counter board. 

So, a bit of a puzzlement in that on 10/15 Meters the operation seems almost normal as you tune the PTO and can detect the Crystal Calibrator. BUT the display does not change. On the front end of the Up Convertor Board are three possible inputs. One is the band signals which have passed through the Low Pass and High Pass Filters, the second is the VLF input which does not pass through the LPF and HPF and the third is the Crystal Calibrator. 

Our noodling tells us that the VCO signal could be tuning a weird frequency range, but the Crystal Calibrator would still be detected. That is what I suspect is happening on 10/15M.

Updated 1-6-2023. TR-7 Block Diagram

(From WB4HFN ~ Inside the TR-7)

This Flow Chart looks like what may be the elaborate plan required to get Mary Jo into the backseat of the 57 VW Beetle. Complex is the operative word if viewed in its totality. But if we take it in small pieces, much like the old tale of eating an elephant -- one piece at a time.

The Color Chart Identification:

1. Blue Lines = Receive Path
2. Red Lines = Transmit Path
3. Purple Lines = PLL Frequency Generation
4. Black Lines = Reference Frequencies
5. Brown Lines = Internal Power Sources

Our prior poking around adventures led us to conclude that the circuitry from the 2nd Mixer Board to the Audio Output and Microphone Input was likely OK. So that leaves the front end of the Receiver and the Final RF Power Amplifier stages. The earlier evaluation concluded also that it was likely 5 boards that could be involved with the root cause of no receive or transmit.

The 1st Board on the Critical Path is the Up Convertor Board and that is where today's sojourn will start. On Receive the incoming signals are moved UP in frequency using the Up Convertor Board. 

Essentially, we have a signal coming through the Low Pass/High Pass Filter array and passed on to a Double Balanced Mixer (DBM) connected to the RF Port. The LO Signal coming from the VCO / PTO PLL where it is amplified by a 2N3866 and connected to LO Port on the DBM. The output at the IF Port is a signal at 48.05 MHz (the 1st IF). Downstream from the Up Conversion is a 4 kHz wide Crystal Filter at 48.05 MHz to act as a sort of a roofing filter.

So let us look at a typical example. If our operating frequency was 21.0 MHz the LO would have to be at 69.05 MHz. Down the food chain is a PTO operating in the 5 to 5.5 MHz range which forms a part of the 69.05 MHz LO signal. A 500 kHz reference signal from the PBT is used in the phase detector part of the VCO to always assure a locked frequency.

Another example with the TR-7 tuned to 30 MHz which would mean the LO is operating at 78.05 MHz. conversely a TR-7 tuned to 2 MHz would have the LO operating at 50.05 MHz. There are two VCO's in the TR-7 with one operating to cover 1.5 to 15 MHz and a second one to cover 15 to 30 MHz.

Let us let that soak in for a bit.

Pete N6QW

Updated 1-5-2023. The Drake Approach!

In the very front end of the Drake TR-7 Service manual, R. L. Drake reveals the "secret sauce" for troubleshooting the TR-7. I have captured their guidance in the excerpt below:

This guidance above seems like a 10-minute task to determine the malfunction typically involving perhaps one board and the resolution involves substituting a known good board. I believe that process is far more complicated than stated.

The best way to translate this Drake Speak is to identify the chasm of stating this process to actually making it happen. 

I call upon our long-standing example of our dear friend Mary Jo of long ago.  It is one thing to fantasize about getting her into the back seat of the 57 VW Beetle and an entirely different matter of actually succeeding in getting her there. There is a huge gap in just how you identify the malfunction and of moving Mary Jo from the fantasy to the reality.

I would like to start with Engineering 101 and that is by stating the problem. "It doesn't work" while true is more of a symptom versus something that is actionable. A Problem Statement must give rise some specific action or group of actions.

So, Pete what is the problem? My approach to developing a Problem Statement is to start by defining what we know.

1. The TR-7 does "power on" with no observable smoke; but does not receive. Because this is a transceiver most likely it will have transmitter problems, but we haven't gone there as yet.
2. A check of the various panel controls and functionalities shows a response by some controls but no actions/responses by others. The AF section is working as is the RF Gain Control (and S Meter). The Pass Band Tuning works as well as the Mode switch. The Crystal Calibrator works, and it appears the PTO is functional in tuning spurious signals but not stations. The PTT and VOX controls works as does the Microphone gain. These were determined to be working by simply exercising the controls. Turn up the AF Gain and there is loud increase of noise from the speaker. Crank back on the RF Gain and the Audio from the speaker reduces and the S Meter pins to the right. Put the rig on VOX and speak into the Microphone and the TR Relay kicks in. Reduce the VOX gain and there is no TR. Engage the Pass Band Tuning, and you can tune across the Pass Band. Move the Mode switch and you can hear the various modes. The Fixed Frequency Transmit or Receive buttons appear to be working. I also tested the external Counter Function of the Digital Display -- it works FB.
3. What doesn't seem to work is that the frequency display does not change as you tune the PTO. Changing the Band Switch causes some change as the display reads 95.8 MHz   on the 160M - 20M Bands and 9.9 MHz on the 15/10M Bands. Noteworthy is that there are two VCO's with one covering 1-15 MHz and the other covering 15 to 30 MHz. So noted that the Band Switch is doing something (but not the right thing) with the VCO. The AUX-7 control does not seem functional.
4. The Up/Down Frequency Buttons seem to do nothing. The Store button if engaged with the power OFF and then ON shows a blank display until that button is disengaged. There is no Noise Blanker, but the Dummy Board is installed.
5. I did discover that the AUX-7 Board was installed backwards and that might have caused some damage to other boards, or the AUX-7 Board itself.
6. The TR-7 uses an "Up Conversion" scheme so as to eliminate birdies and spurs in the ham bands. These up converted signals, outside the ham bands, are processed to pass through the 1st IF at 48.05 MHz and then a second IF at 5.6 MHz is where much of the heavy lifting is done. Within this up/down frequency conversion are four boards, well maybe five boards. We have the Up-Convertor, the VCO Board a Frequency Translator Board, a Digital Control Board and a Special Regulated Power Supply Board. Along with this is the PTO which I believe is working. 
7. I did run a test of the back end of the TR-7 by injecting a 100 MV signal into the stage ahead of the 48.05 MHz IF. This was further proof that the injected signal could be detected in the various modes and that the RF, AF, PBT and 2nd conversion plus BFO's were working. This also proved that the various oscillators on the Pass Band Tuning Board were in fact working. What is not working is the front-end frequency conversion circuitry (the 5 boards). A further test was to inject a frequency of 14.2 MHz following the Low Pass High Pass Filter Circuitry and this was not detected, once again pointing to the frequency conversion (Up and Down) boards.
8. Thus, a formation of my Problem Statement will focus on a Malfunction of the frequency conversion process ahead of the 1st IF which includes the possibility of 5 distinct boards which were previously identified. 

Also recognized is that I do not fully understand the frequency conversion process (5 boards and how they interact). Thus, my next actions will be to fully understand the workings of these five boards. Since I am awaiting delivery of a substitute VCO board, I will also evaluate the purchase of additional spare boards as were identified.

Updated 1-3-2023. A Replacement VCO Board.

The lack of extender boards makes it hard to troubleshoot individual boards -- but not impossible!

One finding in my initial evaluation was that the AUX-7 Board was placed into the mother board --backwards. There were several clues as to this being the case. The Digital Display Board has a series of holes that align with a series of slug tuned coils in the AUX-7 board. These were not aligned. 

Secondly, the AUX-7 card normally fits within board guides on the sides of the enclosure cage. The board was not in the guide slots. 

In most of the other TR-7 boards the bottom socket connectors are in groupings and not continuous. So, if you reversed the other boards then you would not align the pins on the motherboard with the sockets on the plug-in boards. The AUX-7 plug-in board has a continuous socket along the bottom edge thus will plug-in either way.

The AUX-7 Board has two functions well maybe three. The AUX-7 board is mated to panel controls that can operate on a series of fixed frequencies where the board has crystal sockets and individual transistor oscillators. From the front panel you can select either fixed transmit or fixed receive. The slug tuned coils align the fixed crystal oscillators to the frequency of operation.

The second AUX--7 mode is that there is a series of IC sockets where diode steering installed in a matrix via a plug-in header can select ranges other that the normal ham bands. Thus, the TR-7 can be placed literally on any 500 kHz band within the 1 to 30 MHz. This is for receive and by cutting a single trace on the main motherboard this extends to all frequency transmit within 1 to 30 MHz. In conjunction with this functionality the main band switch must be placed in a range so that the LPF is set for the right band of operation. 

The third mode essentially bypasses the AUX7 Board. But this needs further study by me. If the board was installed (not at the factory) backwards by a former owner, then we have the possibility of a smoked board. If the board is truly bypassed for normal ham band operation, then a smoked board may not impact ham band operation. But if the AUX-7 Board must be active even for normal operation, then this is another possible root cause for non-operation. I need to noodle on that by looking at the schematics.

At this point I believe the VCO Board is suspect, but the Hand of God was at hand. I found a VCO board on eBay from a reputable supplier -- it was $68 which gave me pause to think about it. Yesterday, I got an email of a special offer from this supplier -- $55 for one day. I scooped it up. It was guaranteed to be functional. Should I find the issue is some other board -- still a good spare at a better price. My suspicion about this board is that you can access the board pins on the underside of the motherboard - I just do not see any signals of the proper frequency range coming out of that VCO board. 

My sojourn with this TR-7 so far -- a free radio and with an added small fortune, I can have a quite nice 1977 vintage radio. [The MB is stamped 1977 R L Drake Co.]

Updated 1-2-2023. A bit of clarification on the Trouble Shoot Part 2.

This project is a learning journey and looking at only small pieces one could easily get off script. In Part 2, I mentioned the link between the Digital Display and the Pass Band Tuning Board in so far as timing functions. Actually, the link might not be a direct connection as such. 

Realizing this might not be so and lacking the extender boards I looked at the connections on the underside of the main mother board. Locating the pins for the Pass Band Tuning Socket I found the critical signal outputs including the 40 MHz reference oscillator and the 500 kHz square wave "gating pulse". I also saw an output at 38 MHz. So, in fact the PBT board is creating the critical reference signals.

The VCO has several output ports one of which is to supply a signal stream the Digital Counter. That stream appears suspicious, and it does not change, nor does it provide anything other than some sort of "rando" signal at 300 kHz. Another port supposedly supplies a signal to a stage where that output should be at the 1st IF or 48.05 Mhz. That also is suspect!

A 53 MHz signal to the 2nd IF when mixed with the 48.05 MHz IF results in a 5.6 MHz 2nd IF which processed through the 2.3 kHz wide stock SSB filter.

To test some of the follow-on circuitry beyond the VCO, I injected a 48.05 MHz Low-Level RF Signal into the port ahead of the 1st IF. This signal was easily processed through the back end of the TR-7, as I could vary the signal to detect LSB or USB as well as CW and AM. I concluded that the various signals feeding the back end were essentially OK. 

In the wonderful movie, "Casablanca", when Major Strasser is shot by Humphrey Bogart, Claude Rains utters -- Major Strasser has been shot "Round Up the usual Suspects!" In this case the VCO is at the top of the Suspect List.

I am in awe of the Drake Design Team as the 1970's design employed some really leading-edge digital technology.  The use of PLL's and digital frequency generation for things like BFO's and Reference frequencies is amazing and for 1970 was really out there. 

But I also look to today when much of that same electronic magic can be done with an Arduino and a Si5351 variant that has 8 Clock outputs. Today we have a lot less complexity in hardware and more accurate in frequency.

******

1-1-2023 Part 2 /4 of My TR-7 Trouble Shoot!

12-31-2022. My TR-7 Trouble Shoot.

12-29--2022 Update ~ A Great Example of the Classic Trouble Shoot from DL2MAJ

For those unaware my birthday is December 18th and often I will get a combo Birthday / Christmas gift. Last year my #2 son and his wife presented me with a very nice Drake TR-3 transceiver. This was a bit of a family inside joke. 

After finishing graduate school in the mid-70's, I wanted to purchase a Triumph TR-3 sports car. But the XYL wanted to expand the family. It was a bit of a very tense time as to how to resolve the issue. So, we compromised with a family expansion, but I got the naming rights. 

My #2 son was born, and his name is Timothy Ryan (initials TR, so in a way I did get a TR). My #2 son was also aware that one of the Drake Transceivers was called a TR-3. Their birthday card read --You finally get a TR-3 -- the transceiver! [Note if it was a girl, it would have been Teresa Roxanna.]

This same son contacted me earlier this year as he teaches music as a side gig and had a student whose dad, a ham became a SK. I was asked if I could assist in pricing some ham gear the student wanted to sell. In the lot was a TR-7. I suggested that the radio was in such good shape and worked that something north of $700 -900 was probably realistic. In the round of emails, I mentioned that previously I had a couple of TR-7's that I upgraded with the X-Lock frequency synthesizer and that made them rock solid on frequency stability.

So, for this Christmas a huge box is delivered to me and in the box is a "tech special" TR-7 from my son and his wife. The unit is pretty clean inside and unmolested but does not work on Rx or Tx. That said, after a cautious powering up, many of the controls work (RF/ AF Gain, PBT, Mode Select, Crystal Calibrator, and you can tune to the Crystal Calibrator signal (PTO OK). 

The main issue is the display on the lower bands reads a fixed 95 MHz and on 15/10 Meters reads 9.8 MHz. You also do not really hear on the air signals. Despite that the PTO is tuning, the dial readout does not change! My gut feeling is that either (or both) the VCO Board or the Frequency Translator Board are the likely culprits.

This led me to YouTube and the work of Stefan DL2MAJ. He has a five-part series on trouble shooting the TR-7. You quickly see some common threads on troubleshooting like the use of disciplined processes and plain old noodling. He also has a Lazy Susan (LS) installed on his bench top, so it is easy to access the radio. Cool Beans! (Got a LS on its way to me.)

*******

[A post from my former blog and my Christmas Gift to you.]

Three Easy Steps to Troubleshooting!

2/10/2017 ~ See the PS Note at the end.

What, are you kidding? There simply are no three easy steps. So, get over it! That indeed is the heart of the problem --we all want to slide into home, take the easy way out, do the minimum work, send out 100 emails in hopes of having someone else resolve your problem. It just doesn't work that way! I repeat there are no three easy steps! No fellow hams, this is not Fake News!

 

That said there is however a process for troubleshooting a project and that is what I will share with you. A long time ago I came up with my process after observing how heathkit was successful in the kit market until they became a dinosaur and were overrun by the black boxes from the land of the rising sun. Heathkit's success was build and test a portion of the circuit before moving on to the next element. In effect the portions completed actually became a part of the test system as you added new elements. How simple!

 

I like to scratch build my radios and avoid the many kits that are currently on the market. Here is the rub --current kits --you get a board and bag of parts. Some suggest installing all the resistors first and then the capacitors. Or the reverse, caps first. Next install the devices, hook up the wires and give it the smoke test --often it not only smokes; but catches fire too!

So now you have this semi-burnt mess or if it hasn't burned it plain don't work! How in the world do you methodically go about isolating the problem areas? There was/is no testing of what you built as you progress through the bags of parts. One notable exception was the 'softrock" kits from KB9YIG. This was the heathkit model. See the video below --where do you start troubleshooting this jewel?????

 

 

 



 

So here is my process:
 

 Turning on the soldering iron is weeks if not months away. The first steps are to get smart about your project. I call this noodling! Do your homework and research the hell out of it. Be wary of the "Internet Boasts". There is no way you can run an IRF510 with 12 volts on it and from a single device have a 500-Watt PEP linear stage. Ain't gonna happen!

Collect data on similar projects and set up a system that is easy to use so when you need the data it can be readily found. Think in terms of circuit chunks such as an audio amplifier block, a microphone amplifier block, a product detector/balanced modulator block, an IF block, a Mixer stage block, a receiver and transmitter RF amp stage, Band Pass and Low Pass filter blocks. Most of my transceivers are just that, a collection of blocks. An article I wrote for QRP Quarterly on a SSB transceiver was entitled JABOM (Just A Bunch Of Modules).

Using the modular approach serves the purpose of ease of trouble shooting as well as providing a pathway for circuit improvements. Want a Digi VFO instead of that drifty analog VFO --pull the analog module and install the Digi VFO? Want a better audio amp --Boom same drill! The module approach serves another purpose --simply flexibility in how to cram, stuff, and/or shoehorn the boards into that neat metal tin that formerly housed cookies.

I often make cardboard cutouts that are the same size as my module boards and using these cutouts can move them around the enclosure to determine a best fit --all the while mindful of minimizing circuit interaction and unwanted coupling of signals. I can't think of one of my projects that is just a single circuit board. I have over 100 you tube videos of my projects, and you can confirm this for yourself

Backing up from the troubleshooting side is the decision you made early on to homebrew something and with that brings the other side in having suitable test equipment. Don't begin a homebrew effort if you have no means to verify if it is working. Bill, N2CQR has a monthly podcast where I just ride along and have lots of fun talking about radios. Almost two years ago we started an effort to encourage homebrewing a simple 7-part 80M CW transmitter, known as the Michigan Might Mite. We even supplied 3.579 MHz crystals (mostly Bill) for the project. That seemed to be a hit with the listeners.

One ham who competed his MMM emailed Bill and asked how to know if it was working --as all he had was a crystal set and couldn't hear any CW notes. Yes a crystal set --no meters, no O' Scope not even a receiver that could tune to 80 Meters. This clearly illustrates the issue --what a downer to have built the MMM and not know it was working.

Another ham put a Bitx20 on the air and while he could readily hear other stations --no contacts. He asked how he would know if his rig was working as he had no other receiver in his shack so he could listen for a signal. Bill suggested he look at his SWR meter and see if the meter moved in concert with the voice peaks (about 1/2 scale from tune). Yes, No SWR Meter in line and simply didn't have one. So, acquiring some test equipment is very much in order if you want to homebrew your own rig and is mandatory when you have to troubleshoot same.

There are about 6 or 7 pieces that I would put on the list including an SWR meter [Note one of the reasons for low output or oscillating finals is too high an SWR but you would never know unless you knew how the antenna (load) was.] Next would be a DVM (Digital Voltmeter) such as the ExTech series from Jameco Electronics and a frequency generator/counter such as the Feel Tech which can be had for around $50 on eBay. An LC meter (Marlin P Jones is selling one for about $40). To that I would add a DSO (Digital Storage Oscilloscope) such as Bill has the 100 MHz, Rigol about $400. For the ham with the Bitx20 who didn't know if it worked -- if he had DVM, he could have built an RF probe (three parts) where he could see if there was an RF voltage when the rig is fed into a 50 Ohm dummy load which is another item to the list. Dummy loads are easily homebrewed! Take twenty 1K 1/2-watt resistors in parallel --Boom a 10-watt, 50 Ohm resistive load which is good for QRP levels.

OK come up for air and swallow hard -- that comes to around $700. The biggest item is the DSO, but the others can be acquired over a few months of time and are far better than just a crystal set. Should not forget about finding an all-band inexpensive shortwave radio (Sanjean) and that would give you a radio where you could at least find your signal.

To that I would add an isolated low wattage soldering iron-- that Radio Shack 80-watt iron helps heat the shack but not good on surface mount soldering or repair. While we are at it, throw out all of those $1.95 12VDC WalWarts --they are noisy and will make it seem like your project is not working! Get yourself or build a 12VDC, 2 Amp Linear power supply (one with a real transformer). Hand tools are still more items to the list. Trash those crappy Harbor Freight screwdrivers and pliers. I could go on and on -- but why try to do brain surgery with nothing more than a rusty spoon is the message.

This is a really good example of what I preach I should practice as earlier today I was testing the new board and boom the radio went dead. Jostling the board made it come back to life! That could only be an intermittent connection --where was my quality control? See the yellow wire --well when I built this radio almost four years ago, I thought I had properly soldered the wire to the pad. But instead, the wire was just resting on the pad, caught under the resistor so it was making contact. By my handling the board that wire came loose and thus the intermittent nature based on the flexing of the board. I have several pairs of tweezers -- after cooling I should have "tugged on" each wire to assure there was a good mechanical connection --had I done that --the problem would have been found 4 years ago. Good lesson for me and good lesson for you

 

The build philosophy is the next part of my process. Bill, N2CQR and I have talked about this several times. Bill likes to start with what he considers the "tough nut to crack" and since he is partial ( I should say very partial) to analog VFO's --he always starts there. My approach is to start at the back end and build the audio amplifier stage wherein I have a couple of standard designs. [I have committed these designs to circuit boards that are cut on my CNC mill. If I want more "poop" out of the audio I use the NE5534 driving the LM380. A less demanding application would be a 2N3904 driving an LM386-3.]

I know these designs work AND I know how much "poop" they will deliver. So once built I can easily tell if they are working properly! The next element is the Product Detector/ Balanced Modulator. I favor the use of the SBL-1 or TUF-1 DBM for this application. Again, I have templates in my CNC files. Once installed I can hook up to the audio amp and being careful to not exceed 1.414 Volts Peak to Peak (7dBM) inject that signal into the LO port --you can tell if it is working -- any LO signal (any frequency at this point) will give you that test.

At one time I had a small single transistor test oscillator using a 2N3904 and a socket built from a SIM socket ran various crystals into the LO port. The Feel Tech generator will do the same BUT watch the 7dBM --you'll smoke the DBM otherwise. Now with these two stages working build the IF amp stage (consisting of the IF amps and crystal filter) and when that is completed hook that up to the product detector.

If you have that single transistor test oscillator, use that to supply the BFO signal to the SBL-1 and the Feel Tech can supply the signal into the 1st IF. Caution, Caution, Caution!!!!  Loosely couple into the IF stage and run the signal level way down like maybe 50 Millivolts. Loose coupling means using a small value capacitor like 10 PF. The signal generator can be used to sweep the filter about the center frequency. If you hooked a voltmeter up to the audio amp output and if you were using a homebrew crystal filter --this is now a test system! By sweeping the filter and noting the audio output readings you can plot the voltage versus the frequency, and this will tell you much about your filter!

Do you get the point? What you built becomes part of the test system and when you add a circuit, and it does not work --the problem is pretty much confined to what you just added.

Most problems with a circuit can be traced to some common roots, especially when you are dealing with a proven design and what is replicated simply does not work. These root tracings include wrong component installed, bad component, improper wiring of the circuit, cold solder joints, wiring not connected (see the photo above). To digress I love receiving emails that start by saying "Your Circuit Doesn't Work!". One chap who generated such an email sent me a photo of the circuit and had marked voltage levels at every location on the module. At one transistor (a 2N3904) the collector had a "0 Volts" reading which quickly caught my eye. Hmmm 0 volts tells me there is a problem at the collector. Upon close examination of the photo --there was absolutely nothing connected to the collector --it was just sitting there soldered to a pad. Well, here is the rub -- the chap had all of the data in front of him --Clue 0 volts, Clue nothing connected, Clue why it doesn't work. I politely responded that he hooks up the circuit as designed and then it would work. Never heard back from him. But this illustrates the point of how the taking of simple data can often provide the answer.

Another similar email/ photo from another ham reflected the need to improve soldering skills --yes it was a cold solder joint. Many of the components are surface mount and that opens the door to solder bridges shorting out pins or worse hot pins to ground. My process therefore before applying power is to reaffirm right components right place, tracing the wiring to assure correctness and to observe polarities on diodes and electrolytic caps, checking the quality of solder joints especially grounded connections and to look (with a headband magnifier) for any solder shorts! Needless to say --is the power connected with the proper polarity.

More Troubleshooting Wisdom:

I have a stable of proven horses (circuit modules) so I well know their level of performance. I know what works and how well it works. Some argue I would never try anything new -- no --it is simply I will try a new circuit in an existing well understood design. Then if that new circuit adds to the performance, it will now become one of the horses in the stable. A friend is building a project where he is utilizing the Simpleceiver project that was featured on this blog as a part of his project. For the front-end RF amp, he was using the Dual Gate MOSFET (two J310's in a cascode circuit) developed with the Simpleceiver but he wanted to compact things.

 I suggested the use of a single 2N3904 as an RF amp (have used this over and over). Both provide about the same level of gain BUT the J310's offer a way to apply AGC-- but for his application not needed thus the 2N3904 choice. He reported back the 2N3904 was not as good as the J310's --well 15 dB of gain is 15 dB. So that is a clue that there is something needing further attention with the 2N3904 build (not the design). I further suggested simulating both circuit in LT Spice and if you get the same answer on gain then it is how it was built.

 

Soldering skills must be learned! We do not weld our projects (that is a different hobby)! Many problems are encountered that are traced to lack of soldering genes. If the joint looks like it is welded there is a good chance the parts being "welded" have suffered heat damage. Too much solder can lead to poor connections --cold solder joints and often a large welded joint spill over and shorts out other parts. There is also the problem of how to "unsolder" the welded joint. Take time to learn how to flow solder on to joints and how to do it without overheating the parts being soldered. This is where a temperature-controlled iron is vital. Grounded irons are important to prevent static discharge to very sensitive (CMOS) electronic parts. Like I said the soldering part is like the last thing you do!

 

So, OK you bought a kit and as usual soldered all of the caps (or resistors) first and then did the wiring, added the devices and are just about to enjoy your new toy (and without additional checks) when you hit the power and it smokes and nothing more. Before you power up that new radio that took three weeks to come from India (or China) use this process to review what you have done. Are the right wires to the right controls and/or connections, is the power supply polarity correct, etc.? If you go to my website and follow the link or go direct http://www.n6qw.com/Bitx40.html you will see embedded in the building of the Bitx40 all of what is described in this blog post. So, while the focus has been on homebrew the information applies to kit projects too!

 

73's

Pete N6QW

PS: One reader has suggested that analog scopes are available at very cheap prices as many hams have moved to the DSO and these older analog units can be had for pennies. An analog oscilloscope works FB for troubleshooting!