Re: Backlight problem on viewSonic VP171b

You are correct, Jowel80. In my haste and since the MOSFET was in an
SO-8 package, thinking it was an IC I called it "U8" instead of "Q8" as it
really is.

PlainBill is also correct in stating that there could be multiple causes of the
2-seconds-then-blackout symptom. U1 (BA9741), the switcher chip, will
shutdown in the same amount time if either of its two power supply outputs
have zero voltage (which it interprets as a short circuit, thus invoking its
short-circuit...

Re: Backlight problem on viewSonic VP171b

That is a good question since replacing the bad MOSFET might result in
another failure. I checked the resistance across the 4 backlight lamps and
also their resistance to ground. All seemed normal there, or at least
consistent (infinite resistance everywhere).

Update and declaration of success: I received the replacement MOSFETs on
time via FedEx, soldered them in, and reassembled the monitor. It is up and
running and functioning properly.

My conclusion is that perhaps the...

Re: Backlight problem on viewSonic VP171b

I just joined this forum so I could post this reply. I figured it might help out
others who end up in a similar predicament.

With a factory assembly line partially down because of a failed Planar
touchscreen backlight, and no other staff or spare touchscreens available
since everyone was off for the holidays, I was forced to dig into
troubleshooting the EMAX LCD backlight driver board. The board on this bad
monitor is identical to the one cited in this thread.

Thanks to some...