Hello Stan, indeed you told much more to check. Yes these are possible failures with a higher probability and easy to check.
And if no signal generator / oszilloscope is available there are some more DC levels easy to check:
- 2.5V at all connections to T401 and at the active Y-port of IC402 and
- voltages at G, D and S of Q508 for TX and RX (I found two broken Q508 when debugging 8 QMX(+) from other HAM).
73 Ludwig
