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Full Disclosure: Mr. Golden Screwdriver took the case apart to inspect the toroids and try to find why such low power (12V factory build, using full DC power only 2W out).

After touching all 6 of the vertical toroids in the filters area (carefully rearranging the windings), now 30m and 20m are deaf and mute.

I went through the build docs (mine was built at the factory) and did the continuity testing which came out fine.? I tested the 6 1N4007's with a diode test mode in my DVM and they seem fine.? I did continuity tests across each of the 6 coils also which were fine.

80m, 60m and 40m seem to give a solid 2W (the 2W light just lights up on my dummy load) and RX seems fine.? I get no power out indication on the 30m or 20m settings, and on receive the FT8 area of 30m and 20m shows NOTHING on the waterfall.? I used the terminal to initiate the transmissions into the dummy load.

Anyone have any ideas of where else to look for a cause?? What did I let the smoke out of?

Regards,
Mitch
AB4MW

The solution to this interests me as my QDX was working fine (I run it 24/7 with JS8CALL) and then suddenly, 40m, 20m and 30m all stopped working TX and RX, whereas strangely 80m is still working fine.?

It is a self built QDX from the kit. I built it for 12v and I was getting a solid 5w out using 12v.

I thought that as 80m still works then the output stage etc must all be fine and the SDR part.

So the only part that could explain this is the LPFs and the associated switching using PIN diodes?
I have not had a chance to open mine and do any fault finding but was sure I would fine PIN diodes faulty.

I am sure whatever Mitch's QDX fault is, will be mine as well.

regards, Stewart ZR6WT

Thanks Hans for the pointers - I will test and get back

Mitch,
From what you describe it seems like you've got a poor solder joint somewhere along the 30/20m LPF path.
So, a close visual inspection of the board around that area is a good place to start followed by a reflow of the PC-board's connections for that LPF.
Perhaps when you were moving the windings of that filter it was just enough to loosen an cold solder joint?

For isolating signal flow faults, I think it's better to use QDX's built-in diagnostics, AF sweeps, RF sweeps, TX-tests in a terminal session. But, they won't test the antenna connector or signal flow through C2.

You can also test cathode voltages on the switching diodes in a terminal session, too. Searching this forum should bring them up.

Good luck!!

--Al
WD4AH

Thanks Hans,
the LED flashing (I have now re-read that part of the manual) - tells a lot.
All working now on all 4 bands.