My vintage Pioneer SX-2900 stereo receiver no longer produces audio output in either channel. The problem seemed to be occurring gradually over a period of a few weeks. Noticed that it would have audio output when first turned on then lose audio after playing for a while. Each time I checked the speaker output terminals and after a quick disconnect and re-connect of the speaker cables the audio would come back and be fine. But after losing the audio this last time I can't get it back. Pressed the "return" button but no help. Checked all the connections and they seemed to be fine. Checked out the speakers by connecting them to another receiver and they work OK. Replaced the speaker cables but still no audio. Pulled the cover off and found 3 fuses which had no sign of being blown.
Any suggestions about what to check next?