HP 6735s shorted out - Multimeter time!

[spleenharvester]

Hey all. First post so sorry if I'm in the wrong section!

Had a 6735s brought to me. Would power off whenever it damn well felt like, usually when pressing the touchpad. Eventually died, now boots without display and 5 flashing caps lock lights.

Upon dismantling the laptop it's become clear a screw from the touchpad had fallen out and was wedged with the head on the pins of a DC-DC converter, model # Texas Instruments TPS51120, the pins in question are those facing north in the following picture, (can take more pictures of surroundings if need be):

(Just replace dot with ., it won't let me because I'm a new member)

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Touching that area makes the laptop power off in the way it used to so the damage must have been done to that area, if not the TPS51120 chip itself.

Removing the screw stopped the random power offs, but now obviously, the thing is a brick.

Schematic for the chip is here: www dot ti dot com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=SLUS670&track=no

PGOOD1 has 18v going through it when on mains. VREF2 has 9v going through it. I'm thinking TPS51120 must be fried?

Cheers!

 

[grantr37]

hello, you still having problems with the laptop?

 

[spleenharvester]

Hi mate, I am indeed, though I am going to be replacing TPS51120 and a small dual field N transistor next week.

 

[grantr37]

Reflow some of the SMT components first? maybe just track moving.....

 

[spleenharvester]

Already did matey while repairing a nearby SMD cap. The TPS51120 is def faulty, I'm not 100% sure about the transistor (A 2N7002DW, it isn't putting anything out of S2 unless connected to D1) but I'm replacing it anyway.

Hopefully all goes to plan.

Cheers!

 

[spleenharvester]

Some progress guys.

Replaced TPS51120 today after an age of waiting for it to arrive. Fitted it, solder joints looking sweet if I may say so myself.

LEDs at charger point light up. Power button LED flashes briefly. There is a standby 3.3v voltage present, and the correct 18v in present (I have not checked any others for fear of shorting again).

But no response to power button. TPS51120 warms up, and eventually gets quite hot (though nowhere near as quickly as the last one did).

Where else could the problem be?