Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

[sOZQ6tQmi]

Hi all,

I have little experience with board repair, but repaired a motherboard recently (it was a bad cap) and really enjoyed the experience, and now bought a known-broken laptop as a learning project. However it seems I'm stuck quite early on.

Laptop: Dell XPS 15 9570
CPU: Intel Core i7-8750H
GPU: GeForce GTX 1050 Ti
Motherboard: Compal LA-F541P (schematic attached)
Original AC adapter that is outputting 19.38 V

History: I bought the laptop while broken, but the previous owner states it just stopped working one day. There are sings of previous tinkering (worn screws inside)

Symptoms: no sign of life from the laptop. Draws 20 watts (measured at the wall) when plugged in. Took out the motherboard with only the DC jack attached and powered it, still draws 20 watts, and the GPU gets hot quickly. I tried to look for shorts, but I'm not sure if I find shorts or just low resistances where they are expected. I have trouble following the power rails on this board..

No visibly damaged components found


Can anyone provide pointers as to how/where to look? And is it safe to run power to the board in this state? I think I can assume the laptop has been powered like this for an extended time, and it draws 20 watts even when powered off / without fans running. Is the GPU likely to be damaged?

Many thanks in advance! If there's any resistances or whatever that I can measure, please let me know

[Spider1211]

Re: Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

Looks like a dead/fried GPU. Try checking if the high side mosfet for the GPU supply is shorted or not. Measure continuity across PQ1000 & PQ1002.

I tried to look for shorts, but I'm not sure if I find shorts or just low resistances where they are expected.

CPU and GPU will read low resistance.

[sOZQ6tQmi]

Re: Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

PQ1000: 27.1 Ohm
PQ1001: 1.1 Ohm
PQ1002: 27.1 Ohm
PQ1003: open
PQ1500: 0.1 Ohm
PQ1501: 26.2 Ohm


PQ1500 seems to be shorted then? This mosfet is between '+NVVDDS_B+' and '+GPU_CORE_VDDS', so I suppose it could be the one that is faulty?

Do you think the other values are normal here?

[Spider1211]

Re: Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

Yikes, indeed PQ1500 seems to be shorted. Try removing it and test out of circuit. You could also remove PL1500 and check again.

[sOZQ6tQmi]

Re: Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

Thanks Spider1211. I will start by removing and possibly replacing this mosfet. The project will be on hold until Wednesday, when my hot-air station should arrive (currently only have a soldering iron)

[sOZQ6tQmi]

Re: Dell XPS 15 9570: no life in motherboard, GPU uses 20 watts

So I have removed the faulty MOSFET and have ordered replacements, but those will take a while to arrive. Meanwhile I thought (hoped) the laptop might boot without the GPU powered, since there is also an Intel GPU integrated into the CPU.

The laptop powers on and sometimes it stays on, other times it turns off after a few seconds. It seems that once it turns off, it does so every consequent time, and with shorter on-times each time. Anyway it does not POST and there is no image.

When it stays on it blinks an error code (2x amber, 4x white) that should indicate a RAM fault. So I swapped the RAM with another set and confirmed that the RAM is fine in another laptop, and the other laptop's known-good RAM doesn't work in this Dell either.

So here's the question: was it possible for this laptop to boot and just use the integrated GPU, or is it expected not to POST when the power to the GPU is interrupted? What do you think?