If you have a signal generator that can put an S8-S9 signal (abt -73dBm) at the antenna jack, you can use that to trace the receive signal path with a scope.
I used my Elecraft XG3 for this, tuned to a 30m frequency.?
Tune your QMX to the same frequency.?
If you measure at the input pins 4 and 5 on the PMC1804, you should see a sine wave at 12.5kHz, about 300mV p-p.? You have to use AC coupling on your scope, since these pins are biased up.? Same for the 4th and 5th pins down the other side of the chip.? If any of these does not have your sine wave, you need to trace back (via the chips and T401 and L401) to find out why.? Note that the signal goes back to RF on the other side of the mixer chips, so it will no longer be at 12.5kHz, and it will be weaker since it is before the buffers.?
If all 4 of those pins do have a reasonably good looking sine wave at 12.5 kHz, then the problem is with the PCM1804 or with its outputs or supporting solder connections.
