This is preamplifier and power amplifier. The unit had a failure in the amplifier. require a digital voltmeter. power supply, a tuner , a preamplifier ,a amplifier, equalizer.
Have you checked the obvious? It is unusual to have both channels fail at once if the unit powers up. Are you sure the tape monitor loop has not been engaged? That is a common reason for no sound. Make sure it is not switched on. Make sure the speakers are connected.
