Quote:
Originally Posted by xpander
Good reminder cyrano, reforming the old caps gently instead of sudden charge. Have never managed to pop old caps myself so tend to forget this, then again I have usually straight out replaced the old ones. Since Dave has an ESR meter, that should also tell something about their condition?
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ESR measurement is good, but you should also measure the actual capacity left and the leakage current. It's rare for a dried out cap to show a low ESR, but it can happen. In that case, the leakage current will be high.
And for the rest, I'm not a cap guru. I always wonder when I read about brand X being fantastic and brand Y being crap. Afaict, they all make good and bad caps and it's impossible to tell how long they'll last.
And some people swear that Russian high voltage caps destined for use with electrical motors, fi sound pretty good. I've never known any caps to sound better than the usual caps you can get at Farnell or Mouser. Of course, there is a difference between a ceramic disc type, an MKM and a polystyrene cap. And that is important if you're building a mic, a preamp or a filter. But as noise suppression electrolytics, I don't see any difference at all.
I've recently recapped a pair of 40 year old active Philips speakers. Some of the original caps were better than the new Panasonic caps, so I placed them back. These weren't in the audio path, or the filters anyway. And don't overdo it. Don't put a 150 V electrolytic in a 24 V power supply. It will just die sooner, because it can't keep it's dielectric in shape. A 63 V has plenty of margin there, even if the unloaded voltage goes to 48 V.
It's not unusual for an old cap to have increased capacity. That's when the ESR and leakage current will tell you if it's still good.
Increased capacity + high ESR or high leakage current = about to fail.
Increased capacity + low ESR and leakage current = still good.
Decreased capacity + high ESR or high leakage current = dried out. No way to tell if it will fail.
And when it comes to blowing caps, the worst are the safety caps on mains input. Some of these will blow some day, and they will make your workplace and the machine stink for days, if not weeks. I replace those without wondering if they are bad or not. Just to avoid them blowing a week after the repair.