Rich
I would definitely check continiuity through each winding of the receiver transformer. My 40m version looks not as neat as the higher band version in the manual, but the calibration was amazing. Its easy to solder to the outside of the insulation only, so check continuity without touching wire. When all is well, the calibration nulling is amazing. Much of the receiver is audio circuitry. Mine was intermittent so I turned on the builtin signal source,? poked around a and quickly found a loose resistor.
The test audio should be clean. Unlike some qrp rigs, the qcx has generous audio. Maybe your volume control is too high. Peaking the trimmer is not that sharp on my 40m version. But nulling the pots is very sharp, leading to amazing image rejection. Don't fear when meter jumps back up, as the number will change indicating rescaling.?
Motorboating sound does seem to imply audio is overdriven. I would check bias voltage at the regulator.
Curt
