i would first check the power supply first disconnected from the preamp and power amp.
Here is the service manual https://medias.audiofanzine.com/file...ual-472053.pdf
Page 14 has the power supply voltages, if they are not right here nothing else will be either. Forget about the rest of the amp till you get through the power supply.
An welcome aboard, this is a board where techs hang out and help everyone.