No power on any band

[EA5JLE]

Hi!

I received my (tr)USDX assembled because I don't have all the skills to assemble it, so I ordered the one that includes 20-30-40-60-80 meters. The board version is 1.0. I changed the firmware to version 2.00u to test digital media without audio cables.

I tried with the computer's USB power and external power at 12.3V, and the connection was restarting quite frequently. On several occasions, the (tr)uSDX restarted, and after the reboot, the screen sometimes went black, and other times it lit up, but only with dots without information, and the buttons stopped working.

Not knowing what to do, I decided to reinstall everything, the bootloader again, and then the firmware, again the same 2.00u, but this time it checked that the output power is 0.0 watts at 12.3 volts. Previously, the output was 0.7W on 40 meters with USB power.

I don't know what could have happened, and I'm not sure if there's a solution. Any ideas?

73
Fran
EA5JLE"

[dl6sez]

Hello OM,

i think you killed your PA FETs (LO band version 3x BS170) or your PA FET (High and Classic one FDT86256).
The behaviour you expressed sounds like you have a ground loop between your 12V power supply and USB. (tr)uSDX has only simple circuits no real protection and USB isolation as other radios. So it is better to use a battery for 12V when you use USB PC connection. Sometimes a "USB isolator" can help, but depending on the circumstances of your power sources this could be not enough. We all use more and more simple switched power supplies wich have capacitive coupling to L and N and in a standard TN-S power system where N is connected to earth/ground this can lead to a potential difference between ground of PC's USB and your 12V ground. So if you plug both in current will flow and will, depending off the strength, result in a reset or misbehaviour (also killing of the Atmega328 etc. could happen worst case).
Ground loop happens due to power coupling over different power supplies mostly with switched power supplies. Your FETs in the PA were easily killed by txing without a matched antenna or dummyload and we don't know what happened at your "black screen" phases. Also keep in mind stray rf will also disturb the tr(uSDX) because it has direct connections to Atmega328 and no protection circuits there and a plastic case....

73 de Chris

[DL2MAN]

(...)
We all use more and more simple switched power supplies wich have capacitive coupling to L and N and in a standard TN-S power system where N is connected to earth/ground this can lead to a potential difference between ground of PC's USB and your 12V ground. So if you plug both in current will flow and will, depending off the strength, result in a reset or misbehaviour (also killing of the Atmega328 etc. could happen worst case).
Ground loop happens due to power coupling over different power supplies mostly with switched power supplies. (...)

Thanks for that ! I did not think of that, but you´re most likely right and it´s 100% plausible.

73 Manuel; DL2MAN

[EA5JLE]

Thank you for your response, Chris.

The antenna tuning was correct, SWR was below 1.4, and I also used a dummy load for testing. I have replaced the FET transistors (3x BS170), and now I am facing another issue.

It seems that there is a short circuit somewhere, and I am unable to locate it. I have checked the solder joints and haven't found any faulty ones.

I can power the mainboard, and the screen lights up correctly, but when I connect both boards, nothing works, and the short circuit occurs. I suspect the issue lies in the RF board, but I have no clue.

Any guidance?

[dl6sez]

Hello OM,

i think your replaced BS170s were not real BS170 by Onsemi Semiconductor (the original owner and still producer).
BS170 is, because it is a very wide spread and standard used for low frequency switching, copied device by many many other companies!
There are "BS170s" on the market which have a different pinout and can lead to the short immediately if used in a circuit needing the real BS170 pinout.
I think you got this. It is possible because you described the black out with rf board connected.
So just look again for shorts you maybe have made by changing FETs, if none change to original Onsemi BS170s! These FETs are used in many stupid MC circuit but not very widely for rf as we HAMs use them in qrp PAs....

73 de Chris

[EA5JLE]

Wow, I had no idea!

I've looked at them carefully and I can't distinguish any specific brand, only the reference BS170.

Now I have searched for information and found the following note here https://www.etechnophiles.com/bs170-mos ... quivalent/

'Note: ONSEMI recently released a new version of BS170 in December 2021. Its Pinout is different from all other manufacturer's designs: The Gate and Source pins are swapped in this new version.'

I can imagine that the correct transistors are the new ones, starting from 12/2021. Is that correct?