Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL88738

[ZixuTech]

I am dealing with this LA-G341P, which had heavy liquid damage around the Audio board, Battery charging circuit. I went and cleaned liquid areas and left the audio board disconnected.

It had blown PQ1900/02/3 as well as a trace on PU1900. I replaced all 4, and now it turns on and switches off. With a connected battery, it turns on and stays on for a while, even loading the system, then cuts off suddenly.


Charger only - without a battery, the PQ201/PD200 area gets hot. I can see the chipset and CPU also warm up for a second trying to pull up to 2A, then cust off. The Realtek chip gets up to 50*C before the board switches off.
I have removed it to ensure no internal short is causing the fault, but it's the same. The customer already waited a month for ISL and Mosfets, wont be able to wait another month for Audio IC



With only the battery connected, it turns on and off and cycles, although the Audio still heats up.
I have removed the Audio IC again and with battery only turns on for a while and cuts off again. Battery indicator LEDs show that it's empty, though. That may explain cutting down.



With Battery and Charger - It turns on and stays on for couple of minutes and I get these high spikes of 0.9 - 4A - 0.9A, similiar to a battery charging spikes and perhaps detects that the battery is also faulty. I can see that PQ1905 gets sizzling hot to 60*C and makes sizzling sound with alchochol on it. That whole PQ1905/200/208 area gets boiling on short second spikes.



PU1900
PIN 1-2 - 2.37Ohm
PIN 14-15 - 4.65Ohm

It cycles on each of these every sec, so I added both measures before and during the cycle
Charger Only - B+ 13.56V/0A - 13.6V/1.4A
Battery Only - B+ 9.5V - 8.3V
Charger & Battery - B+ 13.34V/1.5A - 11.5/4.8A

+SDC_IN - 18.8V while off 18.4V while on without battery


PQ1900 PIN4 Fluctuates 14.7 - 15.1 without battery and not turning on while I am measuring it
If I measure after it turns on 18.6V

Couple 2R2 looks bit corroded, but they all measure fine including their traces

https://www.badcaps.net/forum/attach...1&d=1666499425
Something on VBUS_DC_SS seems to pull so much current that causes PQ208 to glow to 60*
Same with DC_IN_SS for PQ200

All that said, is there a way to test further without ordering a new battery and audio chip? Just cant hold the customer off for another month.

Thanks

[Sephir0th]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

Dunno where to start exaxtly with your case, but this all sounds pretty bad.

"PU1900
PIN 1-2 - 2.37Ohm
PIN 14-15 - 4.65Ohm"

1. Clarify what exactly you have measured here. Resistance to GND of each pin or resistance to each other?

2. Remove the Audio-Controller from the board. It is obviously bad, no? Are there Shorts around the controller? If yes, remove the controller, check again and if the shorts are gone, just leave it out. The board can work without it.

3. In addition we look at a pretty hot PCH i guess, 60°C or more? First thing i´d try is to find out whether it is shorted or just working (for a short while) and as a result to leave the board as no-fix here and now:

4. So check resistance to GND of all coils (PL400, PL401, PL501 and so on) and share the results here.

imho It should be possible to troubleshoot the board without battery and audio controller.

5. Good luck

[ZixuTech]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

Thanks, @Sephir0th

1. Yes, that's the resistance between the pins of the current measuring circuits. Seems to be within norms?

2. Yes, the second part of the topic was with the removed Audio IC. Still same response, with the difference that only the PCH is heating up.

3. PCH heating to 60*C, and the whole system seemed to work (as it loaded to the Dell logo and was looking for a boot device before even Audio IC was removed) when it was on a battery only for a short time until it drained.
So I suspect we have battery operation. Although adapter+battery and Adapter only are non-operational.
I cannot charge the battery to test more, and I cannot source another one for a quick test.

4. No short circuits anywhere on the lines, as I can locate.

PL401 - 5VALWP - 0.4 - 6 MOhm - 5.1V
PL400 - 3VALWP - 0.35 - 30KOhm - 3.4V
PL1901 - LX1_ISL88738 - 0.52 - 52KOhm - 4.5-4.6V Fluctating
PL1900 - PWR_SRC_AC - 0.63 - 1.5KOhm - 18.83V
PL501 - 1VSP - 67Ohm - 1.05V
PL600 - SW_1.2V - 0.22 - 220Ohm - 0V

GPU coils are around 1.38Ohm
CPU coils around 3.8Ohm

I thought too, but something is causing the system to shut down.
Without battery (removed Audio IC), it turns on, pulls 1.5A and shuts down after 10 sec. I did voltage measurements as well after it switches off.

I come across some manual way to charge a laptop battery, does anyone has more info on this?

Link to schematic - https://www.badcaps.net/forum/docume...top-board-view

[Sephir0th]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

Okay, resistances does indeed look okay so far, then let us assume the best case for the moment, so that just still something is wrong in the DC-IN circuit.

I'd especially check the restored CSMRC lines (Pin 14 & 15), maybe by removing PR1900 and checking the circuit component, by component.

Question: you did replace PQ1900, 1902 and 1903 with equivalent MOSFETs for sure? Share models please if they're not the same.

It might be important to check PQ1901 and PQ1904 too for beeing shorted and also PQ1905 just for sanity.

Unfortunately I can't help regarding the battery charging. Maybe someone else has more experience with this

[ZixuTech]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

PQ1900, 1902 and 1903 and the ISL have been replaced with exact models.

Probed CSMRC lines, even went and replaced slightly corroded 2R2s to make sure they do not muck around. Still same.

No shorts on any mosfets, or anywhere else for that matter.

Only damaged area are the trace on ISL which I reconstructed and these two PC109/10. They are filtering caps with no short on the line and BAT++ voltage being ok there on a battery alone. Unless that upper trace goes somewhere. But I can't trace it down, looks more like a test point.

[Sephir0th]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

With this picture, you missed to share in the beginning, the issue makes way more sense now. Maybe no short to GND, but what about internal layers shorted to each other...?

i wouldn't risk any question marks left and scrape the black carbonized material out till everything looks bright and clean again. After that, if the board still doesn't work as expected, i strongly advice to check whether each pin of the charging controller reaches its destination, so cutted lines and so on and even better, in addition try to make sure, there are no logic or power lines shorted to each other in this area.

[ZixuTech]

Re: Dell XPS 15 9570 - LA-G341P - Power cycling after liquid damage and blown ISL8873

Had to pull the plug, its hard to let go on these almost working repairs, Where you feel you are so close yet so far.

Separated the layer for the battery charger by removing the coils between V+ and B+ which that burned pad is on, but still not turning on without battery. Only time it turns on is with a battery and charger atm, but is unstable.
If there is an internal layer short seems to be under mosfet layers as one mosfet sizzles when battery pulls over 2A

Thanks again