I was in a thread getting information on a failed wine cooler control circuit board.
From the descriptions it seems that the likely culprit is failed electrolytic capacitors, although none show the classic signs.
This started me thinking about a 100W 12vdc to 120vac inverter I have had for years sitting on the shelf.
I bought it for a project that did not happen and about 10 years later I tried it and it would not run.
It powers up for a fraction of a second produces AC and shuts down as if the input voltage is too low.
(No overheating, no sign of over voltage, no blown fuses, no unusual high input current)
Since it sat so long and dates from 2003 when apparently a lot of bad capacitors hit the market, I wonder if one or more bad caps is the problem.
Before I shotgun all the electrolytics, I was wondering if anyone had a suggestion on how to test them.
I do have a multimeter that has a capacitor setting, but was not sure how well it would work with the caps in circuit.
If I have to life a leg, that probably means pulling the cap, and at that point I might as well replace them.
Thanks in advance.

 

Many of the cheap LCR meters on ebay will measure capacitance and ESR using a voltage low enough to be able to test in circuit.

 

That is what I was hoping to find.
A friend doubted you could get an accurate enough test.

 

I tried my UT210E.
It does not seem to reliably indicate the capacitance in circuit.
Anyone have a meter they have had good luck with?

 

Better to remove the capacitor to test it, it will give false readings in circuit.

 

You will have to remove it, other wise you will be charging other things that will effect the reading.

Another way would be to turn it on and measure the voltage across the caps.

In a more general case, if it shuts down, perhaps it is best to probe stuff with an oscope and see what part of the circuit is shutting down...

 

Hi,

How many caps do you have that might be faulty? Usually there are not that many.
In a TV set i think i had four that had to be changed.
In a PC power supply i had maybe six.
If you just change them all to new units you should not have a problem with that anymore. You can check the new ones before you install too.
Sometimes pulling the caps is not hard to do, just make sure any are discharged especially in the higher voltage part of the circuit if there is one.

 

I have an ESR meter and a capacitance meter. Both are very useful.
Here is one but I have no idea how good it is but it is cheap!

Ebay search for ESR meter came up with
12864 LCD Mega328 ESR Meter Transistor Tester Diode Triode Capacitance MOS/PNP

http://www.ebay.com.au/itm/12864-LC...672040&hash=item25cb91eade:g:v5oAAOSwOMdZUx5X

It is almost worth getting one to see how well it lives up to the specs

 

If I have to pull them, I might as well replace them.
I might try skipping the ones that do show close to the label capacitance in circuit.

 

If I have to pull them, I might as well replace them.
I might try skipping the ones that do show close to the label capacitance in circuit.

It's the ESR that is the most likely failure mode, and there might be some small value in testing them in-circuit. But really, the time you spend testing is not worth it. It's easier to place a single order, pay the freight once, and get every single electrolytic on your board. Yes, you have to remove and replace them, but that's usually quicker than almost every other aspect of this chore.

And remember, the caps you don't replace are sitting there getting older. It's not a total waste to replace the still-working caps before they fail. Replacing them all at once should head off the next failure or two.

 

Well, I did not replace them all.
I started with the parts of the board that looked easiest.
Most of the caps I pulled read good when tested.
A couple seemed to show their capacitance slowly (I don't know if the meter reading slow is a sign of a bad cap) and one was
way off.
I did not replace then all because I was having a lot of trouble getting the solder out of the board hoes to install the new caps.
I think it as a through plated, three or 4 layer board with very small holes. My soldering iron did not get the solder hot enough fast enough to suck it out without risking the board.
Since I had found a cap that was bad, I figured it was worth testing to see if the board worked.
It did so I buttoned it up.
I might go back and do the rest of the caps another day (with a better soldering iron.)

I am feeling accomplished. Two broken devices back working in the same week.