compaq presario 18XL2 laptop screen outage
 

I have a Compaq Presario 18XL2 laptop which seems to work fine for the
first couple of minutes after being turned on, but then the screen
goes blank. Once the screen is blank, vertical white lines will
randomly flash on the screen every couple of seconds. I'm fairly
certain this is a hardware problem, because the laptop boots and runs
normally under both Windows ME and Knoppix 3.4 (Linux) operating
systems until the screen goes blank. It seems to be an over heating
issue of some sort, as the screen blanks sooner if the laptop is
already warm. I connected the VGA output to a monitor only to find
that the monitor lost the signal and went blank (but with no random
white vertical lines) as soon as the LCD went blank. This leads me to
believe that the problem does not have to do with the LCD lamp voltage
inverter. I haven't yet tried the TV out or the port expander video
pins.

I completely disassembled the laptop and removed the motherboard. I
couldn't find any damage by visual inspection. The graphics chip, an
ATI Rage Mobility 128-M ENG, is located on the back of the
motherboard.

Any suggestions on what could be the problem and, even better, how to
fix it? I have a fairly sophisticated electronics lab at my disposal,
so desoldering and resoldering isn't a problem (unless it's ball grid
array, such as the graphics chip). I looked into getting a new/used
motherboard, but I'd rather not spend the money. Besides, it's always
fun to muck around with hardware.

Thanks,
josh