Gurus - Ideas? No Power with heatsink installed?

susielam570

Estimable
Aug 31, 2015
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4,510
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Ok, I repair computers and such for a living, so this isn't my first rodeo, but this one has me stumped.

I received a Dell PP29L laptop for a no-power issue. After testing, I determined the dc-jack was damaged and just replaced it. On this laptop, you have to remove the heatsink to pull the motherboard, so of course I did that during the course of repair. I plugged the power adapter and the power-on cable in, so I could test and make sure the laptop would power on. The laptop DID power on, but shut down a few seconds later. Well, the power adapter end was damaged looking, so I tried swapping the power adapter and got the same thing. Then I realized (duh) that I hadn't reinstalled the heatsink.

Ok, so I cleaned up the old thermal compound, put new thermal compound on (yes, I only use a little) and went to power on. Nothing. Nada. Zip. Well dang, I thought... I hope I didn't fry the CPU. But, just to check, I removed the heatsink and tried to power on again. Yup, started right up. Ok. Reinstalled the heatsink... Nothing. Nada. Zip.

Heatsink off, laptop powers up.
Heatsink on, laptop will not power up.

This has me totally stumped. WHY would installing a heatsink cause a device to not power up? My only thoughts would be that it's maybe shorting something out, but I can't see anything it could be doing that to.

Here's a picture of what the heatsink looks like.
 
Is it somehow possible that there could be a trace on the mobo (or CPU itself) that is just starting to go bad/crack, and when the heatsink is screwed down it puts just enough torque on the board to flex it enough to cause an open? I know. Sounds weird.
 
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