Re: 30m QCX working – but not for long....

Glen Leinweber

I have made a guess regarding QCX Morse decoding.....
Am guessing that Hans does receiver decoding and transmitter decoding the same way:
Audio is picked off at IC10B pin 7 and goes into analog-to-digital converter IC2 pin23.
From there, it is digitally processed in a 700 Hz bandpass filter, and its amplitude detected.
Am guessing that if transmit 700 Hz sidetone is Morse-decoded, then audio is present at IC10B
output - this is very near the receiver's output.

I may be wrong: Hans may have pumped the key signal into the Morse decoder, and
in that case, audio digital signal would be ignored.
If my guess is right, then that leaves one stage to troubleshoot: IC10A

Alan's troubleshooting suggestions (added below)  are right-on. Those 10V measurements on
IC10B seem high. A resistor value wrong? Those 10K resistors look similar to 1K resistors.
Alan G4ZFQ wrote:
Are you looking at the manual? These voltages do not match. IC10 pin 5 should be fixed by a potential divider, something around 6V if measured with a DVM, Hans measured 4.2 with the inbuilt meter.
Check R39, 40 and joints around here.
About Q7:
Shows it is not actually turned on. I'd expect the drain to be 0V. Have you checked the resistance to ground here? And you are positive C21, 22 are the right way round?

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