Capacitor Tester

If you have a 50 ohm function generator or a pulse generator and an oscilloscope or a DVM, you can measure capacitance and ESR and maybe ESL, with a little math. Cheap c-meters are often very wrong, and even pricey L meters are often wrong.

This waveform shows capacitance, ESR, and ESL.

It's a 50 ohm square wave driving a polymer aluminum cap.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

That's correct. If whatever meter you have won't measure ESR, you're wasting your time.

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Have you gone back to Tek scopes or is this an old picture, John?

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I dont think i will buy an scope as I would not know how to use it. I also think it falls outside my price range. Are there any inexpensive ESR units?

Also why is it I see many electroic people on the net via utube for example with all sorts of testing equipment Scopes etc. yet they also seem to use Capacitor testers. When would they use them?

Thanks.

That's a year or so old, probably. My bench scope is now the 4-channel

500 MHz (upgraded) Rigol.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

One reason you seem to be confused is that you do not know why you want one.

If you are trying to resurrect something built in the 21st century, an ESR meter is probably the best tool to find the bad electrolytics.

If you have a box full of non-polarized capacitors, and you want to know how many farads in each one, you need something different and and ESR meter will be useless.

If you care about leakage and breakdown voltage, you need something completely different.

If you do not know the difference between polystyrene, mica, and tantalum, then get some more experience and knowledge about practical electronics before you try to measure C.

They're so much quicker and easier than rigging up a scope to do it. Here's the one I use, i know others here prefer other ones, but IMO this one's hard to beat:

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Model number?

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500 MHz is a software thing which you can usually get free if you buy the 350 Mhz (brain-damaged) version.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

This may be the right thing for my simple electronics repairs. Thanks.

Normally I just guess and replace Capacitors. Sometimes it works sometimes it does not. I'm just hoping to save myself a little time and maybe money. It's frustrating destroying the environment because a few Capacitors went b ad by throwing out tons of perfectly good electronics .

It's a hobby not my life long profession, although I Know there are some se rious hobbyists out there. I know many it seems either work for companies o r are former employees of electronics firms. I'm just a shmuck fixing stuff.

Thanks for your advice.

stevw

** For *electro* caps, you need an ESR meter to determine if they are OK.

Like this one.

Google "Bob Parker" ESR meter for info.

.... Phil

Thanks, that's what I suspected.

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It's a nuisance to desolder caps to test them, especially surface-mount parts. It's easier to scope the circuit and look for symptoms of a bad part.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

** There is NO need to do that for ESR testing of electros !!!.

ESR meters use low currents and high frequencies ( 100kHz typ ) to asses the impedance near the component's series resonance.

Electro failure is indicted by an unusually high reading, compared to similar parts.

** Not for ESR it isn't.

... Phil

For a power supply filter, just scope the ripple. If there's too much ripple, the cap is bad; too little C or too much ESR, still bad.

You can learn a lot by probing and thinking. Provided you understand the circuit.

I tell my kids: Measure and think; don't solder.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Depends where in the circuit. In a power supply or audio output, sure--there are probably PN junctions isolating the cap from the rest of the circuit when it's powered off.

In a low-Z RC circuit, not so much.

I have a set of Smart Tweezers that I use for debugging and troubleshooting. I like them pretty well.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

For you perhaps, but not, I suspect, the OP. Anyway, that Peak meter I linked to is able to carry out in-circuit measurements, so except in certain circumstances, it's not necessary to lift a lead.

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I've found some switchers with ripple on the output and it was due to some obscure issue with the feedback path; fortunately it was easy to establish that all the caps were fine and that saved a lot of time.

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** The Peak meter is not generally able to measure capacitance while the part is still in circuit - the instructions leaflet says exactly that.

See final sentence under "Great Service Aid" .

However, it CAN test the ESR of electro caps while in-circuit with rare exceptions and that is the reading you need when hunting for bad or almost worn out ones.

.... Phil