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Pioneer SX990 schematic required to troubleshoot power supply to front panel alumination.

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  • honkytonkin7 Mar 12, 2009

    I would also like to see a Pioneer SX-990 Service Manual to repair the Power Amp Section.


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I have the circuit diagrams and operating/service manual if you still need a copy. My receiver just smoked the transformer today. Hate to see her die, I purchased it in Vietnam in 1970.

You can contact me at

Posted on Mar 14, 2009

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I have a pioneer vsx d503s and the standby light is on. But the receiver will not come on

I sounds like you may have a problem in either one of the Regulator circuits, or, one of the Power Amplifier outputs. If the protect circuit detects DC or Low Impedance on one or more of the speaker lines, it will not fire up the high power section of the power supply. Further troubleshooting will require some working knowledge of power amp and power supply circuits. I've got a .pdf copy of the Service Manual if that will help you.
Please let me know what your level of troubleshooting ability is, and whether the manual will help you.

Apr 30, 2015 | Pioneer Audio & Video Receivers

1 Answer

Pioneer sx-850 goes into protection after several minutes of use. It seems to be after warm up or when room temperature is too high. Summer temps.

Did you check whether the protection assy is working properly? The protection circuit is checking the current of the power transistors as far as I remeber. So there are several possibilities for that fault.
You should grab the service manual or at least schematic ( and then go step-by-step. I recommend to start up with the protection assy itself. If this works properly go for the power amp. It is also not unlikely that the power supply is the cause of the problem.
Good luck.

Dec 05, 2013 | Pioneer Vintage Sx 850 Stereo Receiver...

1 Answer

I have a VSX-D901S Receiver which has been faithfully flawless for many years. Lately it developed a hum/buzz in the front amp when it is first turned on. If I leave it on for an hour or so the hum seems...

Yes it worth to repair it but you must bring into Pioneer factory or service center for Pioneer they are able to repair it
It require to replace a few electrolytics capacitors in power supply regulator if you are in AUSTRALIA it would cost between $150 to $250 to repair it
I hope that give you some idea

Dec 03, 2008 | Audio & Video Receivers

1 Answer

I picked up a technics SL-1100A turntable it is missing the power supply transformer. i require a schematic, or, can you tell me the ac voltage required to operate the unit. my guess is somewhere between...

Hi - I got the manual for the SL-1100 (which I guess is close enough) from the following site:

It has a schematic:


So your guess of 18 volts was spot on!

Please take a moment to rate this solution & let us know if the information given was useful to you - Good Luck!


Sep 06, 2008 | Technics Audio & Video Receivers

1 Answer

Pioneer SX990

I just scored an SX990 in the original styrofoam packing case with a full manual, spec sheets & all at a thrift store yesterday. It looks mint, especially for something ca 1969-70. I'd be happy to make a copy of the manual for you if you haven't been able to find one yet.

Aug 29, 2008 | Audio & Video Receivers

1 Answer

Pioneer VSX-94TXH locks up and requires me to remove power at outlet to resume working

I had the same thing with mine. After a couple of weeks in the local repair shop, it was determined that the main? in-put chip on the back of the front panel was bad. Had it replace for about $125 out the door and it's been working great since.

Jul 01, 2008 | Pioneer VSX-94TXH

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