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Old 14th Aug 2014, 4:29 pm   #101
xrated2
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Default Re: My Homebrew ESR Meter for testing el caps

As expected, it works after switching diodes. Thank you all for helping. David is also right, the 100µA beeing cramped at upper end but iI think it's still OK. For the pot iI just used a 4.7k.
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Old 14th Aug 2014, 5:11 pm   #102
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Default Re: My Homebrew ESR Meter for testing el caps

Quote:
Originally Posted by xrated2 View Post
As expected, it works after switching diodes. Thank you all for helping.
Well done!!
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Old 14th Aug 2014, 7:14 pm   #103
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Default Re: My Homebrew ESR Meter for testing el caps

Anyone who measured in circuit? I got a gpu with 6 blown caps and they measured just fine on the pcb. Doesnt look like they are parallel to each other.
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Old 15th Aug 2014, 12:50 am   #104
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Default Re: My Homebrew ESR Meter for testing el caps

Glad you got it sorted

Perhaps indicating the diode Cathode wires a bit better might have helped, attached is a modified layout with the Cathode connections in Red.

Les
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Old 15th Aug 2014, 1:28 pm   #105
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Default Re: My Homebrew ESR Meter for testing el caps

6 from 9 caps were damaged very obviously but I was surprised to see that the meter showed 0 ohms for all of them. After I removed them from circuit, they showed what was expected.
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Old 15th Aug 2014, 9:10 pm   #106
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Default Re: My Homebrew ESR Meter for testing el caps

You'll find lots of debates and conflicting views about testing the ESR of caps in or out of circuit - most such debates seem to generate more heat than light.

I think you've answered your own question in a way. As with testing resistors, you've got to study the circuit to see if there are other connections, tracks and components which could affect the test. EG, you could check a resistor in series with another, but not one that's in parallel and the same applies to caps. You can spend more time studying a circuit than it takes to remove a capacitor to test it and to be confident in the resultant test. If you do test it in circuit, as you've discovered, the results can be misleading, especially on a complex multi-layer PCB. Nothing to do with the actual ESR meter used - makers of the more swish ESR meters suggest that you can test any el caps in circuit, and in some cases you can, but no ESR meter, however swanky, can override the laws of physics.

Frankly, caps are so cheap, that on a malfunctioning board some years old with several caps, if I found one or two high ESR ones, I'd probably change the rest on sight, because if they're OK now, they probably won't be before too long. It can take as long to test them as it does to fit new ones.

Just my thoughts on the subject.
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Old 16th Aug 2014, 2:51 pm   #107
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Default Re: My Homebrew ESR Meter for testing el caps

The problem goes with some mainboards, having 60 caps on one and its not a fun to replace them all. Especially in the power supply area where the heat goes into the whole layout.
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