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12-20-2011, 08:53 AM
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#1 |
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Member
Join Date: Apr 2011
Posts: 20
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Can a capacitor have low ESR and still be bad?
Can a capacitor have low ESR and still be bad?
I'm wondering, because I just swapped out a bunch of high ESR caps from a power supply, and the unit went from faulty to dead... I checked the ESR on all the parts I put in (didn't have enough new parts around, so I took some from a project I've given up on) Could it be that some of the replacement capacitors have other problems that doesn't affect their ESR readings? |
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12-20-2011, 09:25 AM
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#2 |
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Grumpy Old Fart
Join Date: Aug 2005
City & State: Phoenix, AZ
My Country: USA
Line Voltage: 120V 60Hz
I'm a: Professional Tech
Posts: 10,631
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Re: Can a capacitor have low ESR and still be bad?
If a cap is shorted it will read low ESR.
- The way to tell is to also check DC resistance with a DMM. If it reads low on both it's a shorted cap. - Most caps won't have to be pulled to check resistance. Only need to pull the ones that read low to make sure it's not a parallel resistance issue. If they read high in circuit they will still read high out of circuit. - Also check that you didn't make a solder bridge or a cold joint somewhere. .
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12-20-2011, 06:15 PM
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#3 |
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Banned
Join Date: Sep 2010
Posts: 641
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Re: Can a capacitor have low ESR and still be bad?
The capacitance could also be too low.
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12-21-2011, 07:15 PM
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#4 | |
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Fuhjyyu Killer
Join Date: Oct 2007
City & State: Behind a soldering iron
My Country: New Zealand
Line Voltage: 230V AC 50Hz
Posts: 1,614
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Re: Can a capacitor have low ESR and still be bad?
Quote:
Do you know what ESR value the old capacitors _should_ have been? If your new ones had ESR much lower compared to what the originals had when they were brand new that can also cause issues. (Though I believe that the PSU will still work in such a case, but you will get worse ripple than there should be) |
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01-05-2012, 06:13 PM
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#5 |
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Badcaps Veteran
Join Date: Sep 2006
City & State: Near Cincinnati, OH
My Country: USA
Line Voltage: 120VAC 60Hz
Posts: 704
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Re: Can a capacitor have low ESR and still be bad?
How do you define "faulty" as it was previously? Were the caps visibly vented? I am wondering if you simply caught a PSU fault in its early stages and the existing damage got worse. Electronics like to do that the *next* time they're cold powered on.
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