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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sat Jan 12, 2013 6:54 pm Post subject: Never judge a book by it's cover, same for capacitors. |
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Just because a electrolytic capacitor looks good don't mean squat.
I am repairing a Lexicon pre-amp/processor that is acting much like a funky power supply. I pulled the supply and did a visual inspection and nothing stood out. So I decided to pull all the electrolytics and test them out of circuit even though my ESR meter is "supposed to" be able to check them in circuit. I test them all and all well within 20% of their rating.
Oooops, forgot to check the ESR. Sure enough, there's a 1800uF 10V cap with a ESR of 3.9 ohms. I take a closer look at the cap and the board where it was mounted and see that it has been leaking from the bottom. 
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ecrabb
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Joined: 13 Mar 2006
Posts: 15909
Location: Utah
TV/Projector: JVC RS40, Epson 5010
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| Posted: Sat Jan 12, 2013 6:57 pm Post subject: |
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Lexicon DC-2?
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sat Jan 12, 2013 9:13 pm Post subject: |
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| ecrabb wrote: | Lexicon DC-2?
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Close DC-1
It was picked up for free along with a pile of 2 channel amps and a couple of Crestron devices that were headed for the dumpster (Carver M-4.0t, Parasound HCA-800II and Acurus A250.) Now that the lexicon is fixed, I have something to feed the amps with to test them. Supposedly, one of the amps is missing a channel.
Anyway, I wanted to get this thing going AND I didn't have a 1,800uf capacitor kicking around so I got creative (and brave) and decided to make something that was higher voltage and close enough in capacitance to get it going.
I used two 1000uf 35V that actually measured out to 1935uf. Close enough. Let's give it a shot. Yeee Haaaa
Works perfectly
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Tinman
Joined: 09 Mar 2006
Posts: 1326
Location: Carson City Nevada
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| Posted: Sat Jan 12, 2013 9:16 pm Post subject: |
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This is common. The low voltage caps, especially very high capacity low voltage caps tend to leak.
Being a power supply filter, anything even remotely close, say a 2200uf would be fine. Even a 1000uF would work. Just not as long, because of the aging.
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Motobias
Joined: 08 Jul 2008
Posts: 163
Location: Osnabrueck, Germany
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| Posted: Tue Jan 15, 2013 7:01 pm Post subject: |
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picked up for free with some amps... you suck !
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sat Jan 19, 2013 7:07 pm Post subject: |
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So if you were eyeballing a circuit board for problems, how much time would you spend looking at this?
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sat Jan 19, 2013 7:18 pm Post subject: |
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or this
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Motobias
Joined: 08 Jul 2008
Posts: 163
Location: Osnabrueck, Germany
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| Posted: Sat Jan 19, 2013 7:50 pm Post subject: |
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any cap should get some attention...they suck !
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ecrabb
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Joined: 13 Mar 2006
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Location: Utah
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| Posted: Sat Jan 19, 2013 8:14 pm Post subject: |
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Can't the caps go bad just by evaporation, and show no signs whatsoever of degradation? When I recapped the PSU in my Extron switcher last year, they all looked like brand new. Swapped the caps out, and bada bing, good as new.
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stefuel
Joined: 07 Mar 2006
Posts: 3353
Location: Green Harbor MA USA
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| Posted: Sat Jan 19, 2013 10:29 pm Post subject: |
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And last but not least.....
This is a 1800uf 10V capacitor being seen and measured here. Looking at the display on my meter, which reading would you most be worried about?
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CasetheCorvetteman
Joined: 09 Nov 2008
Posts: 6326
Location: Australia
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| Posted: Sun Jan 20, 2013 11:26 am Post subject: |
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| stefuel wrote: | | So if you were eyeballing a circuit board for problems, how much time would you spend looking at this? |
None at all cause its not attached to a circuit board.
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stridsvognen
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| Posted: Sun Jan 20, 2013 2:08 pm Post subject: |
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| ecrabb wrote: | Can't the caps go bad just by evaporation, and show no signs whatsoever of degradation? When I recapped the PSU in my Extron switcher last year, they all looked like brand new. Swapped the caps out, and bada bing, good as new.
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They sure can.. I have a lot of bad Philips 100uf 25V 030KO axial caps who look perfect.. They can have perfect capacity and bad ESR and the other way around.
http://www.ebay.com/itm/121006773649?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
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Tinman
Joined: 09 Mar 2006
Posts: 1326
Location: Carson City Nevada
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| Posted: Thu Jan 24, 2013 11:13 pm Post subject: |
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| stridsvognen wrote: | | ecrabb wrote: | Can't the caps go bad just by evaporation, and show no signs whatsoever of degradation? When I recapped the PSU in my Extron switcher last year, they all looked like brand new. Swapped the caps out, and bada bing, good as new.
SC |
They sure can.. I have a lot of bad Philips 100uf 25V 030KO axial caps who look perfect.. They can have perfect capacity and bad ESR and the other way around.
http://www.ebay.com/itm/121006773649?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649 |
First of, NEVER buy "vintage" caps. 
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