protection prob's in Pioneer receiver

You guys have been great in helping me.....I'm working on a Pioneer SX850 that has a problem in the protection circuitry. Following the advice of a couple of guys, I've replaced all the electrolytics on the protection board, replaced a C1384 driver transistor....It helped a little. Relay clicks on when unit powered up, audio is clean and no DC on outputs. After 60 seconds or so, relay opens, then comes back on after 30 sec or so. Entire cycle happens over and over now. Voltages on the board drift all I suspect there may be problems on the output boards somewhere.

Is there anywhere I can get a schematic for this beast, without popping forty bucks for a paper copy?

Thanks in advance for your help.


Paid Member
2004-06-06 8:31 pm
Georgetown, On
Hi Jim,
First. Monitor the voltages on the amplifier outputs before the relay. Pay attention when the relay opens.

Second, if the amps are okay you have one answer. Look at the power supply voltages feeding the PCB. Look at one at a time and clear them one by one. Watch for an AC detect line. I don't know if there is one. I have an SX-850 but no schematic.

If the power amps give an offset at the same time, look at the supply feeding the amp PCB.