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Pioneer receiver protection circuit

I have a Pioneer SX-828 with the protection circuit cutting out. I am a low-skill amateur tech, and I cant seem to hit a good repair. Doesn't seem to be a heat issue - may run continuously for two weeks or more, or cut in / out on initial turn on. I have replaced most of the transistors on the protection board and the power transistors for the 35v output on the power supply. Any experience or suggestions what I should try next?

Thank you,
md



Pioneer receiver protection circuit

Your protection circuit is tied to both audio output channels; it senses DC on the outputs to the speakers. Most protection circuits don't fail; if they do it is likely just capacitors going bad. Your problem could be in one or both audio channels.
If the amplifier is over-heating you need to check the bias adjustment; the procedure is in the service information. Since it can operate for weeks this is the most likely problem.
I just looked at the service information for the SX-828 and it appears that Pioneer left out the idle (bias) current adjustment information. When I run across this situation I usually just slowly turn the bias control down (one at a time) while watching the AC line current; when it hits minimum, I turn the control up slightly. This is a very basic way of adjusting bias and may not work correctly in all situations; it is necessary to make sure the amplifier does not over-heat, so let it operate at minimum volume for several minutes.
If you can't monitor line current I don't recommend trying to adjust bias as it can destroy the output transistors.

Pioneer receiver protection circuit

Thanks for you comments. No, I have no way of monitoring current, so I best leave the bias alone. Do you think I have little chance of any success. I admit that I did not understand how the protection circuit works.

Pioneer receiver protection circuit

I have experienced in cases that the screws that hold the power-transistors has loosened
(due to high temp), and needs to be tightened again to get good contact with heatsink.

Just for info.

Pioneer receiver protection circuit

That is certainly somethig that I can try. Thanks.

karodimitrov's picture

Pioneer receiver protection circuit

Check for cold solder joints and also the fuse sockets.They must be tight.Just a guess.