Fisher 634 / 143.97650600 2/4 Quad receiver no sound

[arizonabeach]

Hi, new here. I picked up a Fisher 634 or otherwise known as 143.97650600 Quad receiver last week. I plugged it in and turned to FM source and it worked. Picked up a lot of channels. The meters did not work, but they lite up. I was using the front channels only to test. The micro-tuning volume controls and gyro thingy even worked. Bass, midrange and treble controls worked. Well, then I turned up the volume, not too much, but it stopped working for volume output. I tried every other speaker connection (rear, remote, etc...) and nothing. Tried to use a tape deck for source, nothing. Opened it up, cleaned all accessible controls, reseated the wire harness connectors, checked all fuses top and bottom. Still nothing.

After I turn the unit off for a few seconds, I hear a pop on the speakers, and same thing happens when I turn it on; even with the volume all the way down. If I turn the micro tunning volume controls down, I can barely hear the popping noise.

Any ideas what could be the problem?

TIA
arizonabeach

 

[par4ken]

I would suspect that there is a fault in one of the power amplifiers. The fault triggers the speaker protection relay, which cuts the power to the amplifier. The popping would be caused when the relay switches in and out. That design is a bit unusual usually those relays cut/switch the speaker load not the power to the amplifier.

Check if you can see/hear the relay switching when the amplifier is turned on and off. It might turn on then quickly go off.

Also check the preamplifier output or record output to see if the low level stages are still working, if they are not then possibly it could be the main power regulator.

 

[arizonabeach]

I would suspect that there is a fault in one of the power amplifiers. The fault triggers the speaker protection relay, which cuts the power to the amplifier. The popping would be caused when the relay switches in and out. That design is a bit unusual usually those relays cut/switch the speaker load not the power to the amplifier.

Check if you can see/hear the relay switching when the amplifier is turned on and off. It might turn on then quickly go off.

Also check the preamplifier output or record output to see if the low level stages are still working, if they are not then possibly it could be the main power regulator.

Thanks. When I had the unit out of the case, I watched the protection relay. It closed when powered up, and opened when powered off. Good idea on checking the low level outputs. I'll check that soon. Thanks!

 

[arizonabeach]

par4ken - Thanks for the advice on checking the low level outputs. I tested them (front and rear) and both work. Still trying to figure out why the unit worked when I first turned it on, but stopped when I increased the volume. Scratching my head on this one.