Cap Replacement?

Hermitism

I couldn't figure out what category to put this in becuase they don't have a category for dumb questions. But I've got ask, because I don't know. What creates the need to replace caps. I know over time they can bulge or leak, but is it from heavy use or old age, or both? If I had three twenty year old amps, one new old stock, one moderately used, and one used heavily, would the caps look the same? Or would the heavily used one be more in need of cap replacement? Would the caps in the twenty year old new-old-stock unit be as good as new?

As always, thanks for the info.

skrol

This is mainly referring to electrolytic caps. It is age and/or stress. Bulging is a good sign that they have been stressed. Leaking can mean physically leaking electrolyte, if electrolytic. Leaking can also mean electrical leakage. The electrolyte tends to dry out with time in operation but I suspect a new-old-stock would likely be ok given that it has not been in use.

I had re-caped a Parasound amp (HCA-800ii) and preamp (C/PT-600) from the late 80's and found that 1/3 of the electrolytic caps had gone out of spec based on capacitance. The may have also changed in equivalent series resistance (ESR). These were rather low quality caps. One that was causing the protect circuit not to function properly actually measured good but was preventing the protect relay from switching. I assume the ESR was too high.

More recently, I re-caped a Parasound HCA-1000a that had bulging power supply caps. These were nice Elna for Audio caps. The amp worked fine (save for some broken solder connections). The bulging caps still measure good but probably not for long. These were being operated right at their voltage spec and likely a little stressed.

soundfreak1

At 20 years old you are on the outer edge of thier service life. If it is good equip it might be worth recapping maybe not all depends on what you have give us more info. Brand, model ect.

Hermitism

Thank you for the info. I was just wanting to know for future purchases. I've read on here about people having their equipment serviced/re-capped, but it was something I knew nothing about. I knew this would be the place to ask.

voltz

I don't know, but I heard talk that caps don't like to be left alone for to long, they need to be use and not sitting around for years in a closet and such. maybe others like Ken can say better.

SCompRacer

I had recapped a then 23 year old Class A Krell KSL pre amp with phono board. Some caps were within tolerance, some were way out of tolerance. The ones by power supply had seen the worst heat and were out of spec by over 20%. I bought higher temp rated caps for those positions.

http://forum.polkaudio.com/discussion/142724/krell-ksl-pre-amp-phono-board-recap

Sometimes caps don't look bad. Only way to tell is to measure them. Like are they within or outside their tolerance range (5%, 10%, 20% etc). I have a Fluke 179 that measures up to 9999uf. These Flukes are calibrated before leaving factory. It's a decent meter for the money. Of course at least one leg of cap needs to be desoldered to test. Most caps will need to be removed since they usually soldered tight to board. In circuit testing (both sides connected) does not guarantee correct readings.

In about 10 years, if I still have it, am alive...if I can still hear....if I can still solder...lol I will have to recap this beast. Krell had done it once before. Maybe rebuild the DC servo.

soundfreak1

I just got a technics TT sl1700 had all caps tested and some were way off. Replaced all. Its not uncommon for them to go out of tolerance like scompracer said it just part of owning vintage equip. It may work when you get it but may not be working to full potential as in the my SL1700 it worked ok but would had issues over time.