LA 7912P - Fan spin spins for a second. Then shuts off

[IamPritesh]

Board Number : LA 7912P ( REV 1.0)

Condition in which we received this board : The board originally came to us as not turning on. No lights , no fan spins.

Current Issue: We found that +VSBP was not generating due to faulty P channel mosfet, we replaced it and now +VSBP is generating fine. But we have a different issue now. If I press the power button the fan spins and power led glows for few seconds then stops. I measured and found that we have required voltages on all the coils except the GFX coil. We even have PLT reset and LID switch has 3.3 volt. The amp goes .400 Amps and then drops to .006 . I have flashed the MAIN AND EC bios. I haven't reprogrammed the KBC so far. Any pointers will be appreciated.

Attaching schematic for a quick look.

[ARS]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

From my work on tehese boards i foud out there is a different BIOS+EC depending on Windows. If NTB was sold with W8, you need different BIOS as for W7 board.
And programing KBC is good idea too.

[sikocan]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

Not the same problem, but another Acer VSB issue.
https://www.badcaps.net/forum/showthread.php?t=58904

Correct me if I'm wrong, VSBP means there is power in this line even though it's off right?

[IamPritesh]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

From my work on tehese boards i foud out there is a different BIOS+EC depending on Windows. If NTB was sold with W8, you need different BIOS as for W7 board.
And programing KBC is good idea too.

How do we know which is the correct bios for this. I tried a few available on this site and the result is same.

Not the same problem, but another Acer VSB issue.
https://www.badcaps.net/forum/showthread.php?t=58904

Correct me if I'm wrong, VSBP means there is power in this line even though it's off right?

Correct and we have fixed the +VSB but the board shuts of within a second.

[sikocan]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

Maybe before fixing the VSBP did you check why it wasn't working? Was there a short on this line before you put in new MOSFET?

[IamPritesh]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

Maybe before fixing the VSBP did you check why it wasn't working? Was there a short on this line before you put in new MOSFET?

The fet was defective . There is no short on this line. We have voltage generation right till the vcore and then it shuts off.

[IamPritesh]

Re: LA 7912P - Fan spin spins for a second. Then shuts off

Replacing CPU also has no effect. I also see SATA led glow when laptop is turned on which I find a bit strange.