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Class D Switching Power Amplifiers and Power D/A conversion

Power Rail Capacitors making whistles.
Power Rail Capacitors making whistles.
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Old 7th November 2018, 05:01 AM   #1
shahsalam1 is offline shahsalam1
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Default Power Rail Capacitors making whistles.

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
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Old 7th November 2018, 12:06 PM   #2
Khron is offline Khron  Finland
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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.
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Old 7th November 2018, 12:14 PM   #3
Kay Pirinha is offline Kay Pirinha  Germany
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Your wife is too pretty. Put her or your unit out of the room.
Best regards!
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Old 7th November 2018, 12:16 PM   #4
shahsalam1 is offline shahsalam1
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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.
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Old 7th November 2018, 01:37 PM   #5
Khron is offline Khron  Finland
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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...
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Old 7th November 2018, 01:52 PM   #6
shahsalam1 is offline shahsalam1
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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.
Attached Images
File Type: jpg 20181107_184253.jpg (670.3 KB, 90 views)
File Type: jpg 20181107_184237.jpg (760.5 KB, 89 views)
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Old 7th November 2018, 04:05 PM   #7
Khron is offline Khron  Finland
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And the new ones, that you replaced the originals with?
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Old 7th November 2018, 04:50 PM   #8
shahsalam1 is offline shahsalam1
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Those I replaced are fake chinese capacitor. I think it needs some quality components.
Any suggestions for replacement parts?
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Old 7th November 2018, 08:30 PM   #9
chermann is offline chermann  Austria
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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
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Old 15th November 2018, 01:21 AM   #10
shahsalam1 is offline shahsalam1
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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.
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