T61p short circuit - repair attempt

[TargetAlpha]

Hi,

i've got a broken T61p from ebay. I suspected it was the nvidia bug so i send it to a guy in Berlin to have the GPU replaced with one that doesn't have the bug.
He did that for me before and it worked perfectly.

However, this one seems to have a different problem.

When i plug it in, none of the LED's turn on. It was like this before and after the attempted repair. And the repair guy says it has an overvoltage damage / short circuit thats not repairable. Pah! ^^

So i took it apart and hooked it up to a bench PSU. I turned it on on a low voltage. After i burned my finger on it i found out that the mosfet Q49 was shot. It's a TPC8032. But i couldn't find a datasheet or an identical part.
So i googled a bit and i found this polnish thread: http://translate.google.de/translate?hl ... Fp%3D34860

And it looks like they replaced the 8032 with an IRF7455. So i ordered 2 of them and replaced the part.
I turned on the PSU on a low voltage and the short circuit was gone. I turned the voltage up and i started to hear some buzzing noise. Probably one of the coils i guess. So i turned up the voltage to 19V and the mosfet died again. Short circuit and no more buzzing.

I replaced the 8032 again (Q49) and the 8024 next to it (Q43). I also desoldered the 2 coils next to them (L5 and L11). The coils seem to be ok. I measured 1,7uH if i remember correctly. The short circuit is gone again but the buzzing is back. Even without the 2 coils. Wich is pretty weird i think. L11 is definitely connected to Q49.
I'm afraid i couldn't find the source of the noise though.

Picture here: http://postimg.org/gallery/8i55h2ie/f7c05616/

At 14V it draws around 300mA. I guess all that power gets dissipated in Q49 since it warms up pretty quickly.

And now i'm out of ideas. If anyone has any suggestions, please let me hear them ^^

Btw. all of the testing was done on the naked mainboard. No memory, no CPU. FRU: 42W7653

[TuuS]

If you can get the GPU swapped onto a different board, I have one that is good, except for the GPU. This would probably be easier than trying to troubleshoot it, however I will caution you that there are a lot of fake GPU chips on the market, basically old chips that have had the date codes polished off and re-etched to make them look new. They come from part stripping factories in china. I'm not saying you got a bad one, but this is the reason no one wants to fix these boards. nVidia only makes the chips as needed and only for OEM partners.

If you want the board it's yours for $20 plus postage.