relay matsushita jc2ad-dc24v
Here is a quick check. Find the relay and identify the terminals. Two terminals are the coil, ignore those. The remaining terminals go to the speakers and to the output stage of the amp. When the relay drops out and no audio output by tuning the radio between channels and reducing the volume to zero, measure the DC voltage from the relay terminals to ground. The speaker side should have zero voltages as the relay is open. The audio output side should also have zero volts, if it is working properly.
If the audio output side is non-zero, then the speaker protect circuit is working and you need to troubleshoot the output stage. Often the cause is blown output transistors. This will often burn up biasing resistors and some of the small driver transistors. If only one channel is bad, you can use the other channel for measurements of resistor values, etc.
If the output voltage is zero, then the speaker protect circuit is defective and you need to troubleshoot that section.
---- Steve