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
Stewart ZR1WT