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Hey there,

I had a problem with the same amp so I googled for the service manual and found it! Here’s the link:

https://elektrotanya.com/pioneer_vsx-s51...

I don’t know if your device has the same issue as mine did but here is what i found and did to repair it:

There was a problem with the “POWER TRANS ASSY”, the pcb that supplied power to the entire device.

The amp wouldn’t turn on at all and I measured 0 Volts at all the power connectors to the others pcb’s.

(Continued on next comment)

jake - Reply

So after some measuring with my multimeter to look for short circuits or circuit breaks I found that the following parts were broken:

- The fuse right after the AC INPUT was blown so there was no AC going into the device.

- A MOSFET as a part of the switch mode power supply (I think) was burnt so it made a short circuit (which is why the fuse was blown). I measured a short circuit at several places and i couldn’t figure out which part caused it. So i kept track of were i found the short and compared it with the schematic in the service manual and determined which parts could cause the short. Then I took out these parts one by one and measured if they were broken.

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jake - Reply

You can find the schematic on page 104 in the service manual. The fuse can be found in the bottom left corner right after the AC INPUT labeled “F811 - 250V/6.3A”

The MOSFET can be found in the top-ish right-ish corner labeled “Q821 - HFS7N80” to the right of the “IC821 - L6565”

On page 132 you can find were the parts are on the pcb. The fuse is in the top left corner and the MOSFET is in the middle on the bottom next to the big capacitors.

I replaced the fuse with a ordinary 6.3A slow glass fuse by soldering some wires to it and then soldering the wires to the pcb.

I replaced the MOSFET with a different one because i couldn’t get that particular type. I compared datasheets and found the “MOSFET N-CH 80 FQA7N80C-F109 TO-3P-3 FSC“ (google for FQA7N80C-F109). This one is a bit bigger so i had to bend the pins so that it would fit through the pcb. I also had cut out 2 ribs on the heat sink and put a piece of non-conductive sheet of plastic between the MOSFET and the heat sink. And now the amp works again!

jake - Reply

I hope this helps you to figure out how to repair your amp.

Good luck!

jake - Reply

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