Dead Dell C640 circuit diagram wanted

Hello

This weekend I my C640 died. It was in sleep mode when I went to bed, next day all LED´s where off.

If I connect the power unit the LED goes out (same with another power unit)
The LEDs on the computer are all off
I suspect that the power circuit on the mainboard has a shortcircuit. I have dismantled the computer but can´t find any obvious faults/burnt components. searching the web have indicated that this might be the power FET or the 3V transistor gone bad. But I need a circuit diagram or schematics too find the right components on the motherboard.

Does anyone have schematics for the C640 or have had and solved the same problem?


Henirik

 

Hi
I have had same problem and tracked it down to transistor u45 .Transistor pulls down startup supply regulated by u26 3.3V regulator.Output is on pin3.
U26 sits underneath just behindVGA socket and U 45 is 70mm north U26.
Replace and problem solved.I got my new transistor from a scrapped motherboard.
good luck

 

Hi,

My Dell C640 seems to be suffering a similar short circuit fault. It won't power up from the AC adapter or battery. When I plug it in via AC the led on the power brick flashes on and off, and one of the components on the system board gets *very* hot. (See attachment)

Here’s what I think is written on top of the chip:

F P238L
FDS
6675

Thanks

 

You guys are soldering transistors on your laptops? And successful?

 

Hi
I found a new motherboard on e-bay the other day and have installed it. The computer is more alive than before but not totaly

It charges the battery and when I turn it on all lights go on for aprox 5 sec no sound from fan or hard drive screen flickers slightly and that's about it

If I press and hold F12 on power on, leds for On/of and HD will light after a few seconds bat led goes amber and the the fan starts this will also startup the CD player and the open knob will work and if I insert a CD it will spin

Tried to boot with the Knoppix / Linux CD this way to no avail

I have swapped around processor, graphics card and DDR memmory but it still won´t boot

Any ideas?
Do you have to do something special when you have replaced the motherboard?