Fujitsu Lifebook Power IC gets hot

[bytefarmer]

Hi everyone,
I'm brand new to the forum. I've found this site because I have a very similar problem like this guy. It's also a Fujitsu Lifebook and has the same symptoms: LEDs briefly flash when connecting the power adapter, battery doesn't charge. Same behaviour when connection 14.4V to the battery pins.
I have 0 experience with motherboards but I do have an electronics background, I am an electronic engineer but I have to say there's some dust on that knowledge although I play with Arduino's from time to time.

I was measuring the mosfets like the other post and when I came back from a pause I noticed part of the motherboard was really hot. I remembered some of the power IC's are on the other side of the board so I went looking there. I believe a chip with marking "1285B TI 988 A5HH" get hot instantly when it gets power from the charger. This number let me to a chip from TI: TPS51285A. It matches the pin count and form factor and it does seem to step down power to 5V and 3.3V.
Now, the question is: How do I move on from here? Does it make sense that this chip causes trouble? I did try to trace the B+ rail (keep in mind this is my first guys) and up until now I couldn't find anything suspicious, until I almost burnt myself on this chip...

I want to add that the laptop didn't fail completely at once, it started by shutting down randomly until it definitely didn't want to power on again. We replaced it but it's actually still a capable laptop and I would be extremely happy if I could save it.

[mcplslg123]

Check resistance to GND on 3V LDO/5V LDO on this 1285A IC.

[bytefarmer]

Thanks! That was indeed a logical next step... 5V LDO is shorted to ground, I measured over the decoupling capacitor between VREG5 and GND.
Should I remove the capacitor to see if this is the culprit or.... ?

That 5V LDO doesn't seem to be going anywhere... I can clearly see the 3.3V LDO being lead through an array of via's but the 5V doesn't seem to have anything connected to it...

[bytefarmer]

So I went ahead and pulled te cap, it was fine. I managed to solder it back. It stopped getting hot before I did that procedure. If this is in fact the right IC I'm having 0V at VREG5, 2.4V at VREG3 and 3.7V at VIN

Between Vin and 18.6V rail there is a tiny SMD resistor, measuring 2,2Kohm. This drops about 15V, explaining why I only have 3.7V at Vin. Maybe this resistor got damaged due to the high current/temp?

[bytefarmer]

I bridged the input resistor, since I - with my limited knowledge - think it's 'optional' as this chip can easily take 18.6V and I'm back at a hot 1285A, 3V at the 3.3LDO and 0 at 5. So 5V rail gets shorted out somewhere.