Maker Pro
Maker Pro

What is best way to check capacitors?

M

Mark

Jan 1, 1970
0
I'm having to check several circuits with many capacitors in them.
I have heard of using the following tools:
1. capacitor testor - for out of circuit tests (measure leakage &
capacitance)
2. ESR meter - to check equivalent series resistance while capacitor is in
circuit

What is the best method(s) of checking capacitors? Or what methods would you
use and in what order?

Do you have any specific suggestions on models on instruments you like to
use?

Thanks in advance,

Mark
 
L

LASERandDVDfan

Jan 1, 1970
0
I have heard of using the following tools:
1. capacitor testor - for out of circuit tests (measure leakage &
capacitance)
2. ESR meter - to check equivalent series resistance while capacitor is in
circuit
What is the best method(s) of checking capacitors?

I believe a combination of both, plus any visual clues and temperature
diagnosis.

ANY capacitor that has high ESR requires replacement.

A capacitor that has good ESR might still have a capacity that is below the
rated capacitance and beyond the margin of error. A capacitor that is measured
unacceptably below its indicated capacity requires replacement, especially if
it's a coupler.

Visual clues, such as a burst can, smelly leakage, and/or discoloration on one
or both sides of the board in the vicinity of suspected parts can be indicators
of failed capacitors.

Temperature can also has a big say about how a capacitor will function. You
can spot faulty electrolytics by using air heaters or cold sprays on suspected
parts. A change in performance when exposed to heat or cold could indicate a
fault. - Reinhart
 
P

Peter van Merkerk

Jan 1, 1970
0
Mark said:
I'm having to check several circuits with many capacitors in them.
I have heard of using the following tools:
1. capacitor testor - for out of circuit tests (measure leakage &
capacitance)
2. ESR meter - to check equivalent series resistance while capacitor is in
circuit

A third method is to look at the signal over a capacitor in a live
circuit with an oscilloscope. If the capacitor is good the AC component
should be small. The advantage of this method is that you see how the
capacitor behaves under real live conditions. The disadvantage is that
for circuits like the primary side of a SMPS this method can be
dangerous to your health.
What is the best method(s) of checking capacitors? Or what methods would you
use and in what order?

An ESR meter is ideal for quickly identifying suspect electrolytic caps.
It is the first method I use. It catches the vast majority of bad
electrolytic caps. However a decent ESR is not a 100% guarantee that the
capacitor is good. Like any in-circuit test other components, like
parallel capacitors, may confuse the readings. You still need to
understand what you are doing. But most of the time it works perfectly,
and not having to remove capacitors from the circuit board is a real
time saver.

If the ESR meter is unable to identify you might resort to testing
capacitors out of circuit with a real capacitor tester (not the one you
find on multimeters, these are useless). However before you do that you
want to narrow down the possible number of suspects to test. Desoldering
every capacitor on the PCB and putting the good ones back is usually not
a good idea.
Do you have any specific suggestions on models on instruments you like to
use?

That depends on how much you are willing to spend on it and how
intensively you are going to use it. Is it just for hobby or are trying
to make living out of this?

If it is just for hobby take a look at this one:
http://clientes.netvisao.pt/greenpal/evb1.htm

I have this ESR meter myself, and I'm quite impressed with the build
quality of this unit. It is certainly good value for money.
Unfortunately it lacks a beeper, which makes it is less suitable for
really intensive use.

For other ESR meters look here:
http://www.anatekcorp.com/testequipment/esrcompar.htm
 
L

Leonard G. Caillouet

Jan 1, 1970
0
One important test that we have been using over the past few years is to
re-flow the solder on electrolytics and smell. I have found many caps that
are just starting to leak and test fine for ESR, capacitance, DA, and dc
leakage, and even can be missed with visual examination. It works great for
large caps that you can't see the legs on because of the mounting also.

The best answer to your question is yes, all are important ways to test
caps. Depending on the situation one or all may be necessary.

Leonard
 
L

LASERandDVDfan

Jan 1, 1970
0
One important test that we have been using over the past few years is to
re-flow the solder on electrolytics and smell.

And listen. It'll sizzle like a steak on the BBQ, it just won't smell quite as
great. - Reinhart
 
B

Bob Parker

Jan 1, 1970
0
Interesting that although everyone's talking about testing
electrolytic caps, this specific type wasn't mentioned in the original
post. :)

Bob
 
L

Leonard G. Caillouet

Jan 1, 1970
0
Interesting, indeed. I guess since we (in the consumer video repair
business, anyway) replace a hundred or so electrolytics for every one of
other types these days we just think of them when talking about
troubleshooting caps.

I use a Sencore LC103 for parameter testing for capacitance, ESR, DA, and dc
leakage. Mostly I use the DSE meter of your design because ESR is the most
common way to identify bad electrolytics.

I added a large resistor and a switch to use the same probes to discharge
caps on the DSE meter, btw and it works great to keep from damaging the
meter when testing larger caps that might have a charge. I used to keep a
large resistor with a couple of leads on it but wanted the ease of use and
less clutter and it was pretty easy to add. There is room in the box and
the switch fits at the top center above the display. It only added a few
tenths of an ohm to the lead resistance to go to the switch and I prefer
dischaging them to using the protective diodes. Great product, Bob.

Leonard
 
B

Bob Parker

Jan 1, 1970
0
Hi Leonard,
Yes, it's the electrolytics which cause more faults than probably
anything else, except maybe defective solder joints. :)
Thanks for your nice comments about the ESR meter. I don't suppose
you'd be able to send me a couple of photos of how you installed the
switch and power resistor, by any chance? This is the kind of thing I
like to have on my "ESR Meter Hints" web page for the benefit of other
techs.
I don't particularly like the idea of protecting the meter with
large power diodes either, but I suppose it's preferable to blowing up
the microcontroller chip with an accidental connection to a charged
high(ish) voltage cap.

Cheers,
Bob
 
Top