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Old 10-04-2012, 02:34 PM
jheu02 jheu02 is offline
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ViewSonic LCD Monitor Power Supply Issue

Anyone fix these before? I picked up one with known issues (VG2230WM) assuming it was PS related, and sure enough, I found bulging caps. I had some replacements on hand for the bulgers, but not for ALL the 'lytics on the board. The others weren't bulging and checked good for capacitance, though I don't have an ESR meter to check that. Needless to say, I'll be replacing all the caps after another mouser order.

But to the question: After replacing the caps, I plugged the monitor into my dim bulb tester for power-up. I got an initial start with a small box that said "No Signal" IIRC ( there was no computer hooked up at the time. But then the weirdness started. After about two seconds the once dim bulb began to brighten and the monitor shut down, to then go into another start-up sequence. This kept repeating.

So, which came first, the chicken or the egg? Was the DBT limiting too much (normal for monitors?) current causing the shutdown/repeat? Or, could there be some other component issue that could cause the shutdown? I had a 100W bulb in there, so I wouldn't think it was the DBT's fault, but this is my first monitor repair. I'm used to shutting off the power if I get a bright bulb in amp restores, but are flat panel LCD's a completely different beast when checking them?
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Old 10-04-2012, 09:36 PM
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old_tv_nut old_tv_nut is offline
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Repaired one Viewsonic by replacing the whole power supply board. I'd just note that the components-only repair kits sold on line include caps PLUS some of the power supply ICs, so it may be common for these to take out the ICs also when the caps fail.
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Old 10-04-2012, 10:19 PM
jheu02 jheu02 is offline
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Quote:
Originally Posted by old_tv_nut View Post
I'd just note that the components-only repair kits sold on line include caps PLUS some of the power supply ICs, so it may be common for these to take out the ICs also when the caps fail.
That's what I'm wondering, but since I'm not quite sure how the DBT might be affecting the power up, I didn't want to start desoldering transistors, etc to check them yet.
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Old 10-04-2012, 10:39 PM
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Eric H Eric H is offline
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I'm no expert on these things but I don't think a solid state device like a Monitor would like running on reduced voltage, kind of like running it during a brown out.

When the Monitor started running it probably drew more current, making the bulb get brighter and dropping the voltage, Monitor shuts down and it starts all over again.

Did you try plugging it in directly and see if it stayed lit? If it didn't blow up before you recapped it it shouldn't blow up now and the fact that you saw the "No Signal" box sounds like it was working.
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Old 10-05-2012, 05:20 PM
jheu02 jheu02 is offline
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Unfortunately I didn't try it on line power as I'm spring loaded to shut things off if the DBT goes bright. In working on a tube amp I was getting a false DBT because I was using too low of a wattage bulb, which was staying lit the whole time. Once I went to a 100W bulb, I got a good dimming when checking out that amp. So, I thought with a 100W bulb it would be a valid test, but perhaps not working with the voltages in monitors.

I'm planning on pulling the transistors over the weekend and check for oddities, but I've already repurposed the replacement caps into some tuner recaps I'm doing, so I won't be able to power-up the monitor until I get my next mouser order in.
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Old 10-16-2012, 02:37 PM
jheu02 jheu02 is offline
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Update...It Works!

Got my full compliment of caps in today, so I got them soldered in, power straight from the line voltage, and voila...a fully functioning 22" widescreen LCD with a very nice picture.

Tried it again with the DBT and the results were the same as earlier...startup screen, bright bulb, shut down. So, the DBT is too limiting with monitors and TVs due to the voltage/current involved.

Thanks for all the help and suggestions.
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