troubleshooting Pioneer receiver
I recently inherited a SX-850 Pioneer receiver. Nice unit, walnut case, lots of knobs and silver front.
Problem is, when it's powered up, it plays for about six seconds maximum, and then the protection relay clicks. No sound. Shut it down, turn it back on, same thing.
I understand this is an extremely common symptom with this vintage of receiver. I was on www.oaktreeent.com website, many many of the old receivers for sale there had the same problem.
Anybody have any experience on this? Where do I look?
I have a lot of experiance with old Pioneer units. Usually there is a transistor that drives the relay coil, and as it ages the C-E voltage eventually rises to the point where it chews up enough voltage that it can't engage the relay. The possibility of old dried-up caps in the protection circuit is also a real possibility.
It is also possible that the protection circuit is simply doing its job, and you have excessive DC offset at the output. Check this first.
Also look at the averaging cap in the protection circuit. As it ages, the circuit will begin to detect normal music as a fault condition.
You didn't state if there was audio when this occurs, I am assuming there is. Otherwise you may have intermittent DC offset. Check the DC conditions across the speaker terminals with no audio playing.
check the FM center tune meter, if it is way off center, the +35 regulator failed.
replace the 2sc1318 with a larger 2sc1384. per bulletin
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