Ok.. FINALLY got this saga of the Compqa Presario C500 done.
Initial cause of problem: Lightning or huge power surge that shorted out darn near EVERYTHING on the board: battery, power plug (it was melted), power plug WIRE going to the board, screen, screen power inverter, memory and motherboard itself.
I went through I think 5 different inverters and tested on 2 or 3 different screens to find out what problems were where.. replaced the small stuff first, got it up and running after replacing power adapter and memory and hooking up to a monitor to discover that the motherboard I got to REPLACE the damaged one, was itself defective (HP issued a recall but I missed the deadline last summer) in that it would send a signal to the screen, but the inverter was not getting enough signal or power (and I tested this with at least 5 different inverters) from the motherboard to LIGHT the board - note, I tested the inverter and the screens on MY OWN laptop, and I know they all work.
So I shipped the bad mobo back off to China.. never to be seen again. This was about a month ago.
Yesterday I got the replacement motherboard and promptly went to work putting it back together.. Once I realized that in my LCD monitor fixing craze I had taken the backlight OUT of the screen that was currently mounted to the laptop and put in a screen that HAD a backlight, I was back in business again and it's up and running.
It has a mysterious bulge in the upper right corner, presumably from a wire I took out of a plastic channel to make things fit again.. I've made sure all the screws are in place properly and can't find another reason for the bulge.. but I don't really care.. I'm just happy to have a second working laptop on hand.
Wondering if anyone else has had these many problems with a single type of motherboard?
