Power Rail Capacitors making whistles.

[shahsalam1]

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 somebody please guide me what is causing these capacitors to go bad.
Sharing the amps schematic for this amp will be highly appreciable.

ABDUSSALAM

 

[Khron]

Are you sure it's not some inductors making the noise?

On the other hand, the ESR of electrolytics goes down with increasing temperature, so that might explain the noise changing, though.

 

[Kay Pirinha]

Your wife is too pretty. Put her or your unit out of the room.
Best regards!

 

[shahsalam1]

It is definitly caps. When I press capacitor's top noise changes. And if i manage to press all four capacitors, amp becomes silent.

I suspect may be I am wrong about rectifiers that they are creating some sort of excessive noise at their output.

 

[Khron]

Some photos of those capacitors would be interesting to see. I'm willing to bet they're some bottom-of-the-barrel crap brand / no-name ones...

 

[shahsalam1]

Pictures of original capacitors which I later desoldered are attached.
They say 'tf CD268 2200uF 50v'.

Will replacing these with better one resolve the issue.

 

[Khron]

And the new ones, that you replaced the originals with?

 

[shahsalam1]

Those I replaced are fake chinese capacitor. I think it needs some quality components.
Any suggestions for replacement parts?

 

[chermann]

Hi


caps which are used in smps. less ESR at higher Frequencies

e.g. 3,93 Amp ripple current @ 100khz = Chemicon EKZN630ELL222MM40S

others:
Nichicon UHW1J222MHD

Nichicon UHE1H102MHD6
Panasonic EEU-FC1H152L

Epcos (TDK) B41858C6278M000

 

[shahsalam1]

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.