EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: cincin on May 03, 2023, 10:21:39 pm
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Hi!
I'm working on my stereo amp that has problems. I've been using ChatGPT to help me along instead of pestering you all with my beginner questions, and it thinks it's likely a capacitor on the power supply board. There's only a handful of them so I started pulling them out to test with my LCR-TC2 multi-function tester.
The LCR-TC2 underestimates the capacitance a bit compared to my Fluke 115, but it also gives me ESR readings that are off the charts.
The first cap I pulled is a 3300uF 50V, and it gives me a 37 Ohm ESR reading.
The second one I pulled, a 2200uF 50V gives me 26 Ohm ESR reading.
I pulled out some new capacitors: 2 new black Nichicon 1000uF 16V gave me 24 Ohm readings, while a gold Nichicon 220uF 63V gave me no ESR reading at all...
According to the charts I find, they should have around 0.1 Ohm of ESR.
These are all repeatable results and I am confused.
Is my LCR-TC2 just inaccurate?
Are these ESR possible?
Are my caps just all bad?
Obviously this all points to my LCR-TC2 being bad, which is pretty sad since it's new and from a reputable eBay seller, but I would still appreciate confirmation on that.
What are reliable yet affordable ESR meters if this LCR won't do?
Thanks!
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Is my LCR-TC2 just inaccurate?
Are these ESR possible?
Are my caps just all bad?
Obviously this all points to my LCR-TC2 being bad, which is pretty sad since it's new and from a reputable eBay seller, but I would still appreciate confirmation on that.
What are reliable yet affordable ESR meters if this LCR won't do?
It's not unthinkable that your $5 multifunction tester has an issue. There are reliable LCR-ESR meters in the $100 range, but you probably don't need them. On solid state linear audio power supplies I can't recall ever seeing a bad capacitor that measured OK as to capacitance but failed on some other parameter, at least not badly enough to cause a significant issue. I've seen plenty of bad electrolytic capacitors, but your Fluke 115 should be good enough to catch them.
If you still want an LCR meter, others here have recommended the DER DE-5000 and at that price point (about $100 or so) I can't think of anything better.
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Thanks! That answered many questions at once. Cheers!
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You have to set the frequency of your LCR meter to the same frequency the cap was tested at.
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You have to set the frequency of your LCR meter to the same frequency the cap was tested at.
How do I do that??
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How do I do that??
'Good' LCR meters use an AC test signal and measure the reactive impedance. Some (and the DE-5000 is one) allow you to use different frequencies for the test signal so as to allow you to compare results to a spec sheet more easily. Common test frequencies for electrolytics might be 100Hz to 100kHz. Neither the tester you use nor the Fluke 115 use the AC method so this isn't relevant to them.
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'Good' LCR meters use an AC test signal and measure the reactive impedance. Some (and the DE-5000 is one) allow you to use different frequencies for the test signal so as to allow you to compare results to a spec sheet more easily. Common test frequencies for electrolytics might be 100Hz to 100kHz. Neither the tester you use nor the Fluke 115 use the AC method so this isn't relevant to them.
Right, I was just reading about that procedure, and how to do it manually with a signal generator and an oscilloscope. Cheers for the clarification.
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According to the charts I find, they should have around 0.1 Ohm of ESR.
No, they don't have to have 0.1 Ohm.
1) The smaller - the better.
2) 0.1 R - That's too much for so large caps.
3) You better look at datasheets. Yes, electrolytic caps have datasheets too.
Cheap ESR-meters measure ESR at frequencies in between 50-150 kHz, instead of 100 kHz, but this doesn't really matter much for repair. Bad cap mostly will have ESR gone far from a limit. It's a rare occasion when ESR is close to limit and it may mean that it is better to recap it, because it is worn.
ESR of a good healthy cap will be twice as better as a limit datasheet value. So there is quite a good margin. You just have to calibrate you meter or get used to its measurements first. You may play with some new good caps for this. After such calibration it becames an easy task.
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I have an LCR-T4 and I seem to remember that there's a
calibration procedure. Maybe the LCR-T2 also have one?