Troubleshooting: How to dama... no, how to REPAIR your (tr)uSDX

[dc8lz]

Hello!

I like to start a short (keep fingers crossed) thread what to do, if something fails.

Maybe we should sort and rewrite this article later on. But I will start with two parts:

Do NOT, Take Care

- If your truSDX is under power be aware to NOT contact/short the ISP connector to the RF board. This can happen f.e. if your trUSDX is not in a case. In the end your PTT Line (or others) of the Atmega will be damaged. Hint: Isolate the ISP header or the RF board on this position with a tape.

Harmless Probless

- No TX Power "SWRnan0" in the display. This means that the SWR check was "critical" or completely wrong. Main reasons: One or two wires of T1 and T2 on the RF board are not (good) soldere. Especially two of them goes to ground and there the solder temp (maybe) was not be perfekt. So check the solder points with a magnifying glass f.e. Do not try to measure the contacts via DMM, most of them are DC short (check circuit!).

- Nearby no output power. If you see nearby zero watt measured in the display, attached a dummy and the SWR shows 1 your main pcb may have a problem. Measure pin DRV on the pin header. There should be a rectangle with about 5.8V PK-PK on TX in CW. You can do this safely with only the main board. But I alwasy recommend to lower the voltage (maybe 6..7V so that the LDO can outout 5V) and with a max current from round about 100mA. A bad soldered 74ATC00 was the problem here. Just some pins were not that flat on the surface and so the solder looked good but it was bad. Resoldering solved the problem.

...to be continued...

[dl8bag]

Hi,
measuring the output with OHR-WM2 the (tr)uSDX seems to have about 100mW powered through USB and about 2W powered with 12V on 7MHz. Does it make sense to invstigate how to increase the output power. Losing/gaining 3dB is not that much and may be due to deviating component characteristics.
Vy 73 de
Rolf, DL8BAG

[DK2CW]

Hey,
you could try optimizing the output filter for maximum power by spreading or compressing the windings on the coils (corresponding to the tested band).

This approach is shown for the QCX in this video:
https://www.youtube.com/watch?v=eN7wER05T-c

[edmund]

The USB port is not intended for the overall supply of the device. The available 5V are too low for the HF output stage.
To increase the performance at 12V the output filter can be optimized as already mentioned. But then the harmonics should be controlled. Mainly the 2nd one (14MHz) is critical.

[DL2MAN]

Well, nominal it is
4-5W @12V and 0,5W @ 5V
SO you are below nominal.
Well worth investigating what exactly went wrong.

73 Manuel; DL2MAN

[dl8bag]

I will check what goes wrong. Output is the Same on all bands though. The transmitter transmitts on the intended frequency and looks like a sine wave (in CW). Testing it with powering via USB might reduce the chance to fry the BS170 finals.
Vy 73 de
Rolf

[dl8bag]

Tx Drive is set to 4 and PA bias max to 128 - would that explain 100 mW @ 5V? Anyway I will try to tweak the windings on the toroids somewhat.
Still a transceiver constructed and developed by geniuses
Vy 73 de
Rolf

[DM3FAM]

Hello Rolf.

If you have made any progress, let me know. I too have far too little output power on all bands, despite changes to the windings.

73 Marcel DM3FAM

[dc8lz]

Hello!

Ok... it is nice to have more than only one kit on the desktop...

We had a nearby zero output kit. The 1st idea about a problem in the RF board was wrong since the problem still exists after changing the RF board (with a well tested one).

So the next thing is to check the "Drive" (marked as "DRV" on the pin header) and the TX part. Just looking on the cicruit you see that there are not that much possibilities. One idea wass that Q1 may be damaged. Another idea that C1 was missing/bad and for sure: What about the 74ACT00?

And this was the problem: One side of the 74ACT00 was a bit lifted and so some solder points were bad...

So how to check for example if the main part is ok (always if testing... limit the current, take a lower voltage, here f.e. 7V) if you measure the Drive.

Take a oszilloskope and measure the drive "DRV" pin on the header on TX in CW. You can work with only the main pcb. You should get a rectangle (nearby sine, depends on measure equi...) with a high peak-peak voltage round about 5.8V (frequency of course the one you have choosen).

73 Stephan

[DM3FAM]

Thank you for help @Stephan. Glad that the problem was found this way.

73 Marcel DM3FAM

[dl8bag]

I havn‘t made any progress so far. Output is still the same. It is the same in every band. Drive shows about 5.8V when RF board is removed. With the RF board plugged in it is about 4.8V. I started with 40m and squeezing the turns did not change the output power. Removing 2 turns did - it is now even lower. I will wind the toroid again with 9 turns and See what happens. Although it is quite improbable I will check the BS170s as well by removing one after the other and see what happens
Vy 73 de
Rolf, DL8BAG

[DL2MAN]

Yes, please check the BS170s.
If one is faulty, it will heat up more than the others, and reduce your output power.

73 Manuel; DL2MAN

[dl8bag]

Hi,
I had success. After I removed one of the BS170s I have 13.2V on 80m, 10.7V on 60m, 10V on 40m, 10.8V on 30m and 8.8V on 20m (always peak to peak and powered via USB) and of course transmitting into a dummy load. Although tweaking migth help to get some more output but to me it seems to be working now. --> "Was für ein geiles kleines Gerät" in english: "A really very cool gadget"
And murphys law didn't seem to apply: the first BS170 that I removed led to the increase of output power.
Vy 73 de
Rolf

[DM3FAM]

Thanks for the feedback Rolf. It's nice that it works now. Have fun and maybe see you soon in a (tr)uSDX - (tr)uSDX QSO

[dl8bag]

Yes,
That is (a qso) what I am looking for. Does it pay off to search for matching FETs - after some hours of optimzing the output I don't believe that it does but I read that it would reduce harmonic distortion. Currently the transceiver has at least 5W output on every band when powered with 13.8V. Some way up an om provided a link to a youtube video where he explained how he optimizes the output of QCX transceivers - that helped a lot for me: check, whether it helps to reduce the number of turns of each toroid of the serial resonance matching network - but this may be different for each (tr)usdx.
Vy 73 de
Rolf

[joemen]

I May have done just the thing you wrote of first.
My Tr uSDX was going well untill I tried to improve my 20 meter band.
I got SMOKE .

[Faraaz VK4JJ]

I May have done just the thing you wrote of first.
My Tr uSDX was going well untill I tried to improve my 20 meter band.
I got SMOKE .

Which part has blown up?

[joemen]

Not sure yet, it powers up still on USB 5 volt and 12 volt power supply.
Oled lights up, I can change Bands and go through all the menu.
I can't see anything burnt but I did see smoke. No power out.
It was all going so well, I guess I am just HAM fisted.
I dont have a lot to test properly here, really gutted.
Will test on Rx tonight, terrible wind today in UK.
I hope its just the 3 BS170, anything else I'am Fubar.

[dl8bag]

Do you own an oscilloscope? It helped me to find a cold joint that I produced. I would connect the trx to USB and check whether the 74act00 produces rectangular output while transmitting. If so, you are half way through. Can you receive any signal on any Band? You should - otherwise er check whether the antenna connector is soldered properly - I had a cold joint there. I had a cold joint on the PCB so that the trx worked with USB but not on 12V.
Hope that you will be successful. The moment you have your first QSO with is simply great.
Vy 73 de
Rolf, DL8BAG

[joemen]

RX ok on CW and sidebands , CW decoder is very good. Well done Guido
The tests on half size (g5rv) , the strong winds have taken my other antenna.
Do I have an Oscilloscope ? .
Well, yes I do if you count a COSSOR 1035 from the 1950,s.

[dl8bag]

Certainly - that will do. You can check whether you see the square waves when you key the transceiver in CW on the output side of the 74act00.
Vy 73 de
Rolf, DL8BAG