Help me determine if these caps are good or bad

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Hello DIYers,

8 years ago, while replacing an LED in my Pioneer A-605R integrated amp, which I had bought new in the 90s, I noticed the filter caps were slightly bulged (top is slightly curved). See the pictures, thought they don't show much and I couldn't take more revealing ones.

I said I'll address it later as I was about to move. Being a major move etc., I totally forgot about the caps.

Until yesterday when I removed the amp from the wall unit to redecorate. I suddenly remembered THE CAPS and rushed to remove the cover expecting to see a disaster. Nothing!

Does bulging always indicate degradation or failure? Could they be domed by design?

I'm thinking the caps are OK because:
*Both caps are domed similarly
*The bulging did not get worse with time - they look the same like I remember they were 8 years ago
*No leaking or other visible abnormalities
*Amp sounds fine - no hum and no distortion on power-demanding passages

I didn't measure yet for drops in rail voltages, or for ripple, during high draw. I don't have ESR or capacitance meters.

The caps are 15000uF 50V 85C. No brand name printed on them but the look like Nichicon Gold. They show ACH7046-A 622.

What do you think? Replace or forget?


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I bet they came from the factory like that. I'd measure the ripple voltage to be sure. If the ripple voltage is reasonable (maybe a few volt under full load), I'd leave them alone.

It looks to me like the bulge was created when the cans were scored on the top. I bet that was done by mounting the can on a rod and ramming it into a T-shaped edge. The score is there to ensure that the can opens safely (rather than as a hand grenade) if the electrolyte in the cap starts to boil.

The only reason I can thin of as to why the caps would bulge (if they did not come made that way) is that they are overheating when in use. Play the amp with the cover off, and feel the caps after it's been on for awhile. They should not heat up on their own, if not warmed by nearby hot components. If they do get quite warm, then the internal leakage current is high and it's time for replacements.
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