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DOA Capacitors

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¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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I have a number of LCD monitors that have all suffered from a particular fault at one time or another -- swollen and possibly dried out 105C low ESR filter caps on the 12V and 5V rails of the power supply (switchmode).

When I purchased the capacitors for the second monitor, I bought enough to do the rest (and then some).

Recently one monitor died, and then a day or so later another one did.

The first one I opened up had a combination of capacitors fail I had not seen before. Only the 5V filter caps were swollen, and in fact leaking. Also they were ones I had replaced about 3 months earlier.

When I grabbed the replacement capacitors, I noticed that one of the new and unused ones was already sporting a bulging top, and measurements revealed it had a much higher then expected ESR. The other three new ones were fine.

I can only imagine that one or both of these new capacitors I had installed three months earlier had been faulty.

These capacitors were unused, and stored in very benign conditions.

The second monitor had the typical pattern of failure with both the 12V and the 5V filter caps affected by heat/age, and was one I had not repaired previously. So it was just a coincidence that two failed in two days.

The place I got the capacitors (Jaycar) is unfortunately staffed by people who don't care. I showed them the new capacitor and they just shrugged. I would have expected them to at least say "that's odd" or something.

The capacitors in question were 10V 1000uF low ESR. I have found that 16V 1000uF low ESR caps have a much lower ESR (about 40% lower) and also have a form factor that better fits these boards, so the second monitor got these.
 

shrtrnd

Jan 15, 2010
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I read an article a year ago, saying the Chinese had a shipment of incorrectly mixed electrolyte, and they didn't find out about it, until they started getting reports of failures
in the field. The bulk of the caps made were supposed to go into hand-held devices,
and the manufactuer was hoping the life-cycle of the hand-held device might be shorter
than the life-expectancy of the caps they had installed in them.
I don't know if yours was a similar problem. But wanted to let you know, that I had
heard, at least in China, quality control is not there. And some bad electrolyte got into
the supply chain.
I also read, the manufactuerer wasn't going to honor any replacement policy, because
the caps should have survived their limited warranty time, by the time they failed.
Just trivia to consider. Odds are, you got some bad caps from a bad production run.
 

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¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Yeah, I've heard of most of that, including Chinese quality control.

I've never experienced a capacitor failing *before* use though.
 

Resqueline

Jul 31, 2009
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That's incredible.. Blown right out of the bag.. What brand and type are they?

Bad electrolytes are one of the modern "diseases", very likely for the reasons shrtrnd mentions.

I got some "Nichicon HZ's" from Hong Kong once. The printing on them looked dubious and the cross-hatch in the top was the wrong pattern - so they were fakes.
They measured a slightly higher ESR than real Nichicons should've had, but were not too bad and are still holding up in a USB-HD PSU I put them in.

Yes, higher voltage, and physically bigger cap's have lower ESR's. Better to fit as big as fits.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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They are Suntan -- not the best brand, but the only one available locally.

When I first got them, Jaycar was out of stock of the 16V 1000uF capacitors, so (although I tried) I didn't even get to see them. This time (12 months later) they had plenty, and the good news is that they are almost exactly the same size as the original, and slightly lower in height than the 10V units (which are long and skinny).

The first repairs were done out of curiosity, on the basis I had nothing to lose. The first fixed monitor has been going for in excess of 12 months using the caps right next to the ones which failed after 3 months. It will be interesting to see what pattern develops.

Incidentally I use these monitors today as "extra" screens. I currently run 5 monitors on my PC. I was down to 3 the other day! :D

I demonstrated the obvious problem and fix to a colleague a few days ago. He was quite amused that the first step is "find an empty plastic drink container" (but that's another story)
 
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