# Pioneer GM-D8604 Power Rail Capacitors making whistling noise.



## shahsalam1 (Nov 7, 2018)

I bought a used Pioneer GM-D8604 4 channel class D amplifier a few weeks ago.


I suspect that it has been repaired before. It looks like FETs and rectifier ICs have been replaced.*


The problem I have been facing is that the "Power Rail Capacitors" make high pitched noise only when amp is cold.When amp warms up a bit noise becomes less. I replaced the capacitors 50v/2200uF and the noise problem had gone. But after a week the noise came back.*


Can anybody please guide me what is causing these capacitors to go bad. If anyone has schematic for this amplifier? If so kindly share schematic.

Abdussalam


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## bnae38 (Oct 3, 2015)

You're sure the noise is from the caps and not the transformer? Pretty common for them to "sing". I usually shut them up with some red rtv, but it isn't really a problem..


Are there any problems besides the noise you hear from the amp?


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## JCsAudio (Jun 16, 2014)

shahsalam1 said:


> I bought a used Pioneer GM-D8604 4 channel class D amplifier a few weeks ago.
> 
> 
> I suspect that it has been repaired before. It looks like FETs and rectifier ICs have been replaced.*
> ...


Funny you bring this up. I had bought a D8601 years ago from Best Buy new and it did this exact same thing by making a high pitched noise when cold. I ended up just returning it back then but now own a D8604 and have no issues with it. That was about 5-6 years ago I think.


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## shahsalam1 (Nov 7, 2018)

It definitly were caps making noise. If I press them noise was gone.


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## shahsalam1 (Nov 7, 2018)

Yesterday, I replaced all 4 FETs IRF 3205. Put the original capacitors back in. 
Tested. Amp works completely silent now. It appears the problem has solved.1


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