Dell XPS 15 motherboard sudden death, no clear sign

[Orsu]

Hello,

This is my first message on this board.

My 4-5ish years old dell xps 15 (laptop) suddenly died the other day. Irrelevant, but i opened a pdf file and it very suddenly stopped with no warnings or nothing.

I couldn't get it to boot again, so i tried unplugging the battery and the cmos and doing it again. To no avail.

The diagnostic LEDs (link, if it's useful to you: https://www.dell.com/support/kbdoc/en-us/000141206/a-reference-guide-to-the-xps-notebook-diagnostic-indicators) just stay white before stopping. Removing the RAM did got me the amber code indicating a memory problem, but plugging it back in didn't fix anything.

Plugged screens don't display anything, or detect a video signal.

I then stripped the motherboard of everything i could, and i see no obvious defect or problem.

I plugged it in and tried booting to see if there was an element getting particularly hot, and nothing.

The only thing i guess, is that when i removed some black tape there were bit of solder sticking to it, but they were just "there" not really soldered to an element.

What should i try? Am i cooked? Is providing pictures any help?


Thanks for suggestions, this (was) my daily driver, and i can't really afford a new one right now.

[indeterminate]

Please list the exact model

[Orsu]

It's a xps 15 7590

https://dl.dell.com/topicspdf/xps-15-7590-laptop_users-guide_en-us.pdf

I managed to find the same board, but this one has a different CPU on it. https://www.parts-people.com/index.php?action=item&id=31529

I can't tell for certain whether the cpu or some small component on the board has given up on life

[indeterminate]

At a minimum you will need a multimeter , oscilloscope & fine probes.
you will need to get a copy of the schematics for your particular pcb unless you have a lot of spare time.

This is a very very complex and difficult thing to repair, the fact that it does sumthing when you press the power button gives you a place to start.
it could just be a simple fault in one of the power supplies

if you have a static safe work place and a 10x > 20x magnifier you could go looking for dry / cracked solder joints
you could be lucky.

[Orsu]

Do you know of a repo where i could find schematics?

And so you would check each component one by one then ?

Yeah, time consuming, but let's say it's for reuse reduce recycle

[armandine2]

And so you would check each component one by one then ?

if it has happened to you it has probably happened to someone else - and somebody then probably did something helpful

[Sorama]

Repair shops (almost) never use schematics.
We do reverse engineering :-)

[Orsu]

So you go thermal camera + multimeter under a low voltage, and go to town? Do you know of particular things to watch out for, or noobies "gotcha" ?

[Sorama]

First of all, one needs to know if there is a short or not.
For that you need a power supply with current indication.

If there is no short, thermal analysis is useless and so is injection.

One needs to understand how the power rails work, if they do work and if not, measure relevant components that make it not work.
Scope is not essential, not at all.
A good multimeter is and often the only thing you need (a transistor tester is also nice to have).

Often it is a capacitor (open or short), a resistor, bad solder or a fet.

 Not processors, nor ram.

The YT movie here is a bad example; that guy lacks basic knowledge but just tries swapping things until it works.

[u666sa]

What should i try?

When you connect PSU to your laptop, what is consumption when nothing is pressed? How about when you press the power button?

Since you have mobo out, measure voltage after first and 2nd mosefets. What you getting?

[Orsu]

I plugged in a psu with amperage, and after pushing a button i got either 0.1A, 0.3A and no lights, or 1.5A,1.6A and some activity (blinking lights, fan turning on)

Just plugging, like 0.1A, oscillating to 0.0A (i guess it's just under what it can measure)

Which mosfets are you talking about? Starting from the power side?

I found a schematic, i think it's the correct one: https://drive.google.com/file/d/1GLOYRT8I6JDVwMpKhGZAXKU5zy4qnRrr/view (LA-H331P)

I took the cleanest pictures i could, i'll document what i do as i do it

Thanks

[u666sa]

Fan turning on is good, main power rail not shorted. First two mosfets are good.

What you got there controlling power? BQ chip? Find which one you have, find datasheet, and check for voltages on it.

The above is important.

Meanwhile



Measure resistance to ground on all the coils.

[Orsu]

I picked up the mobo to work on it the other day, and it somehow got worse by itself, the lights don't turn on anymore

I'll some more later

[Orsu]

While probbing around, something shorted very clearly and a smd cap melted. Maybe someday i'll try to do something using a thermal camera and whatnot, but right now i don't understand the schematics i found, i don't have any of the replacement smd components around, and i cannot spend much more time on the board fruitlessly.

So i gave up and ordered a replacement one from Aliexpress, because it was the cheapest option available to me.

I will update the thread if it turns out to have been the good choice.


Thanks everyone