les wrote:
I have the model VG800 LCD and have looked for the schematic online, but
have not found it yet.
However, here is the problem.
When I power it up, the green light lites, then an image flashes for a half
second
then disappears. The light remains on. It can be reset, and the process
repeats itself.
I tested the external power supply with a 5 amp load, and it manitains 12
volts.
So I assume there must be a logic switch internally that trips off.
Can anyone familiar with this model give me more specific ideas?

Most likely* bad caps or decoupling in the supply to the
(backlight) inverter. Viewsonic's are plagued with
this problem.

*YMMV