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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


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.