Auto tuning with 50w should not be a problem. It should work and it should read something close to the 50. Regardless of whether this is a PIC that has a 4 or 5 volt reference. I think these devices mostly use the version with a 4.096 Volt reference. I believe the maximum power the design? can read is roughly 150W so extrapolating a bit the voltage you are seeing is too low to represent your power level. I would be looking at the bridge peak detector diodes or their filter capacitors. Not very likely to be an associated resistor voltage divider unless the thing got hit with a over power situation and was damaged. Guessing the diodes blow out first. I think you can remove the diode and check with a scope that you have the sampling voltage at the 10 turn coil and then figure which peak detector component is bad. I would check the detector diode pretty carefully. I think the series resistor and the voltage divider likely go a long way to protect the PIC underr bad circumstances.
regards,
john
