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Viewsonic 15 inch LCD hard to turn on

OK, I got a 15" Viewsonic VA550 LCD monitor for 99 cents at the thrift store.

Very occasionally, I can get it to turn on. Like 1 out of 100 presses of the power button. About 1 out of 20 times, there is a quick blink of the power light, but usually nothing. A strong light reveals that it is not just the backlight, there is no picture.

If I hold the power button down while plugging in the power supply, about 1 in 3 or 4 times it will turn itself on. When on, it looks great.

I tested the power supply, and with the back off I can see a green LED on the back of the video board is on when the power supply is plugged in.

Once it is on, it stays on.

I've checked the power button contact resistance, it seems fine, and shorting the pins with a metal object doesn't turn it on any more reliably. Reseated the 2 ICs in sockets, and reseated all connectors. Close visual inspection, don't see any visible cracks or damaged components, no fishy smell or strange miscolorations.

Any ideas? I've never worked on an LCD monitor before. I've already found a few references online stating that Viewsonic refuses to provide parts or service manuals.

Thanks, Steve Greenfield

Reply to
polymorph
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Once it's been on for a while can you shut it off and turn it right back on or does it still act up?

Reply to
James Sweet

I would suspect the power supply, as in a switch mode that is shutting down from turn on surge. It may be a sensing resistor that has changed value and the sense circuit now thinks it draws too much current and shuts it down. Or an IC is actually starting to draw too much current possibly after a small surge from a storm. If it will run a while and turn off and on correctly, Try hitting diff IC's with freeze to find which one is weak.

Reply to
James Thompson

It still acts up. I have the back off, but have it laying back down so it still gets warm. Leave it on 30 seconds or several hours, shut it off, it still won't turn on again. I can hold the power button down while plugging the power supply in, and most times it will then turn on, as before.

Steve Greenfield Polymorph Digital

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Reply to
polymorph

Reply to
swohlfarth

I didn't see anything obviously leaking or smell the typical fishy smell.

Looks like I need to build an ESR meter.

Thanks, Steve Greenfield

Reply to
polymorph

Reply to
swohlfarth

Clever. The high voltage means it isn't well suited to in-circuit. Any reason not to use a higher frequency to minimize the affect of the capacitive impedance? Most ESR meters seem to use 50KHz or 100KHz.

That's good though, clever, quick and dirty. Actually, if you put a couple of shottkey (sp?) diodes across the leads, the output can't go high enough to trigger a silicon junction but it shouldn't affect the ESR reading.

Steve Greenfield

Reply to
polymorph

Reply to
swohlfarth

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