Capacitor testing - LCD monitor

August 30, 2012 at 20:45:46
Specs: Windows 7
I have an eMachines 21.5" LCD monitor, model E211H. It's about 3 yrs old & I've had no problems with it until now. I noticed some slight flickering last night just before I shut the system down, today it won't come on. Actually, it flashes the display for about a second & that's it. Everytime it's switched off/on, the display flashes. I figured it was one or more of the capacitors, so I split the case & removed the circuit board. Unfortunately, there is no obvious swelling or leakage from any of the caps. I don't have a caps tester but I do have a decent multimeter. My question is about how to properly test them & whether or not I'm doing it correctly.

1. discharge the cap by shorting it with a jumper wire
2. using the ohmmeter (I have it set to 20K), touch the black lead to the cap's ground & red lead to cap's positive

As I understand it, if the cap is good, the meter should immediately drop to near 0 when the leads are connected, then count up to infinity as it becomes charged by the multimeter's battery, is that correct? That appears to be what's happening with all but 2 caps. They are both 2.2uf 50v. When I touch the leads to them, the meter does nothing. There are 2 other 2.2uf 50v caps that count up to infinity like all the rest.

Does it sound like I found the bad ones? I'm not an electronics wiz so if I'm doing it wrong, please let me know. I'm pretty good with a soldering iron though so assuming I tested correctly, I'm thinking it would make sense to replace the all 4 caps of that size even though 2 tested good, just to be safe.

Thanks for your help.

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August 30, 2012 at 21:28:53
That's how I understand the program too and agree you found some bad caps. I'd replace 'em (all 4 while you're at it) and see if it fixes the problem.

Pretty cheap repair even if it doesn't work

Audares Juvo

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August 30, 2012 at 23:27:08
Most of the time, caps are good unless they're leaking or puffy.

Most newer multimeters can test capacitors, although I'm not sure if they can test for leakage. When testing caps in-circuit you have to remember that you're actually testing the capacitor in parallel with the rest of the circuit so the readings may not be accurate.

I noticed with a capacitance meter I had several years ago that electrolytic caps were harder to test and readings were less accurate.

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August 31, 2012 at 08:40:50
"you have to remember that you're actually testing the capacitor in parallel with the rest of the circuit so the readings may not be accurate"

Good point. This thing is dead in the water anyway so I figure I have nothing to lose by trying what I'm trying. I'll remove the suspected bad caps & see if they still test bad off the board to confirm. More than likely I'll just replace them anyway. I'll post my results later.

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September 3, 2012 at 08:46:42
Quick update - the 2 caps I removed tested bad, so I replaced them. I didn't bother with the others (yet). I was anxious to see if it would work so I benchtested. The eMachines logo comes up for a second or 2, then the screen goes black again, so I'm going to replace the rest of the 2.2uf. If that doesn't do it, I may just replace ALL the caps - that'll probably cost another $5.

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