Pioneer VSX-859RDS with all mosfets gone

[debruina]

Hi,

I am working on a pioneer VSX-859. It started with only one problem but i ended up with a lot more. Probably caused by me

Anyway it started with a DSP NG message on the display. That one was easy and was caused by a bad 5v rail. Replaced the capacitors and the message was gone. Everything seems to be working except for a blob sound every time i switched from source. Eventually i tracked that down to a leaking battery on the analog board. Repaired some via's and lines and everything worked ok. That same circuit also caused a not working DCdetect protection.

Except something went wrong when I put everything back together. I forget (not sure that was the cause) to connect the flatcable between the driver board and the power mosfets. The flatcable may also have connected with ground. Not sure, long story short: it blew out 8 out of 10 mosfets and emitter resistors in the power module. I replaced them all and after power up, they where gone again. I found out the flatcable between the powermodule and the driverboard was bad. Replaced it and now i need a way to test it.


I disconnected the power supply from the amp board and connected my own +-30V power supply that I limited to max 0.5A. I tested all channels and they all work. So i know the mosfets work but i cannot test it completely with the filter/relay board.

Now i am looking for a way to limit the amps own power supply. In case something is still wrong. The power supply has a +45 / -45 voltage with 2x 22000uF capacitors that goes directly to the power module. So if something is still wrong it will go out with a bang. Does anyone have any advice how to test the amp? Is putting some low value resistors in the +-lines of the power supply <> power module an option?

(in the first pic the amp module is removed. Picture three shows the module, it has its own power lines red,grey,blue for SBR/SBL and red,black,blue for FR/FL/C)

[petehall347]

Re: Pioneer VSX-859RDS with all mosfets gone

use an incandescent lamp in series with the ac mains power .

[debruina]

Re: Pioneer VSX-859RDS with all mosfets gone

use an incandescent lamp in series with the ac mains power .

It's difficult to get it powered up with the lamp in serie. Even with disconnected power module. because of the big buffer caps

[CapLeaker]

Re: Pioneer VSX-859RDS with all mosfets gone

Use a higher wattage light bulb or multiple light bulbs.

[debruina]

Re: Pioneer VSX-859RDS with all mosfets gone

Use a higher wattage light bulb or multiple light bulbs.

That did the trick. I was able to power it up. All mosfets are still in one piece

Connecting a speaker resulted in a loud hum and amp going in protect. I measured about 5 volts between the negative speaker terminal and the chassis. Then i remembered the funny thing about pioneer amps. They need a screw between the relay board and the chassis to ground the speaker terminal and now it works!

So i think it was me that forgot the screw in the first place in combination with a DC protect circuit that wasn't working because of a leaking battery. Not connecting a flatcable causing the mosfets gates floating in nothing probably didn't help either.

Anyways it works now. Thks to the both of you for the lamp trick

[CapLeaker]

Re: Pioneer VSX-859RDS with all mosfets gone

The lamp trick works awesome, you just have to increase or decrease the wattage of the light bulb with whatever you are trying to repair. Something that draws a lot of current, you need a higher wattage light bulb. A small PSU is something like 60w maybe 100w. I use 150w a lot for these PSU’s that I repair.