Yes, without having the diagram myself, the power supply would be a good starting point. Most units have two DC outputs, one at five volts and another at twelve or eighteen volts to power the tuner and amplifier stages. Most transformers will ahve an input/output rating on them and these would be AC voltages. Checking voltages at large capacitors would be a place ti start and voltages should be two thirds to three quarters of the capacitor voltage rating marked on each. No DC voltage with a good AC voltage would indicate a failed rectifier.