Hello, I have been working a customers laptop for about a week now.
Here's the problem: It is a Compaq Presario F500. It was brought to me because it would power on, but black screen, no external display. So I figured it was the same problem all F500 and F700 mobos have, the nVidia chip. So I did the penny trick and left the laptop on for several hours. Ok. I come back plug in a external monitor and power it up. Laptops boots into Windows and works fine with external monitor.
Now comes the problem. I go to put the laptop back together and as soon as I plug in the LCD's video cable into the motherboard the laptop looses power. It kinda acts like it's a short somewhere. The fan clicks a little as if it's trying to start, there is a noise coming from the speakers, no lights come on, no beeps, only sign of power is the DC Jack light. Unplug the video cable and laptop powers up normal.
So the symptoms are:
ONLY when LCD video cable is connected laptop will now power on.
Fan makes clicking sounds as if trying to start.
Speakers make noise about every 5 seconds.
No lights, No beeps, No Power
When LCD video cable unplugged:
Laptop boots fine with external monitor
Troubleshooting already performed:
Checked in known working machines; RAM, HDD, LCD, LCD Inverter Board, Video cable, Power Switch, DC Jack,
Changed the whole motherboard and problem still persists.
Any help or suggestions would be greatly appreciated.