DOn't worry about the voltages.
STart with making sure power amp in jack si OK. Patch a cord from preamp out to power amp in and see if it helps.
Put a signal into the power amp in jack. Is that OK, or does it react the same way?
I'd be betting your output stage is not running on all cylinderrs.
STart with making sure power amp in jack si OK. Patch a cord from preamp out to power amp in and see if it helps.
Put a signal into the power amp in jack. Is that OK, or does it react the same way?
I'd be betting your output stage is not running on all cylinderrs.