Dead HP6735s via TPS 51120 short

Hey all.

Here is the laptop's entire schematic: **broken link removed**

We've written this one off anyway but I want to see if I can get it working again, because science.

HP 6735s came to me with a random power off fault. Eventually quit working completely with 5 flashing caps lights. Screw head had fallen from touchpad and was wedged on the bottom row of pins (facing north in the following picture) of the TPS51120 at the time of it dying, along with a brief squeal noise.





Sometime later while taking measurements I accidentally shorted TONSEL (which should have been 2v but was actually 18v) with PGOOD1 - now PGOOD1 puts nothing out and the TPS51120 chip gets scaldingly hot within seconds (along with no power). Not too worried because TPS51120 seemed to be toast anyway

Here are some voltages I took before this event.


Most probably TPS51120 causing the fault before considering the nature of the short? Any tips for resoldering?

Cheers!

spleenharvester said:

TPS51120 chip gets scaldingly hot within seconds (along with no power).

Click to expand...

It implies substantial current (a few amps) is going through it. No surprise if it is robbing power from other circuitry.

You will get abnormal readings until that device is out of the power loop.

After that, there could still be a problem in other components.

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?

I believe there are many tests which must be passed before startup gets to the point of showing any message onscreen.

I would not be surprised if a lot of these tests are volt levels at various test points.

Your OP shows the results of many tests. Have you done these again? Did the results change? Can you do them both when cool, and after the IC heats up?

Did you try removing all accessories, in order to simplify the process?

Does it make a difference whether you start up from battery power, or from an AC adapter?

I tried to magnify the schematics, but they always get resized to fit the screen. I cannot tell where the TPS51120 is located, or what circuitry it is associated with. Have you detected any problem with nearby components?

Check Power On Button For 3.3 Volt is present or not ?

spleenharvester said:

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?

Click to expand...