XPS 13 9360 no CPU power

[ytsoc]

Hello , i came across this dell with water damage. after replacing some coroded resistors i have the folowing problem: PU1000 is not starting up, it does not start producing voltages for cpu.

You can find the schematic and boardview here

When i press the power button i get 3.3V on pin 40 for 1-2seconds, so it is receiveing a command to start but there is nothing on the output vcc core and vcc gt, however i get 1v on vcc_sa

When measuring pwm freq (multimeter, no osciloscope available) input to PU1100 i get 58khz(for 1 second, however no voltage on output coil) but nothing on input of PU1102


What sugestions do you have?

[mon2]

Re: XPS 13 9360 no CPU power

Remove all power.

Meter in resistance mode (200 ohms).

Check the resistance to ground on each and every coil.

[ytsoc]

Re: XPS 13 9360 no CPU power

nope, no shorts on any rail, on pl1100&1102 i have 6-7Ohm

[mon2]

Re: XPS 13 9360 no CPU power

1) voltage on +5VALW ?

2) if you have VCC_SA then this implies that pin 30 of PU1000 is sending out signals ? (PWM_VSA)

[ytsoc]

Re: XPS 13 9360 no CPU power

1) 3.3 and 5V are present, same for voltages on other coils excpt for these2

2) it would be a logical conclusion, moultimeter reads about 450khz

Edit: managed to swap pu1000 and i get the same behaviour: no output for core voltages but VCC_SA is still operating the same way

[silvake]

Re: XPS 13 9360 no CPU power

Lately I'm trying to fix another LA-D841P board who had the same fate (liquid damage) and I amazingly noticed in here the description of EXACTLY the same symptoms and behaviour, just as in @ytsoc 's case. Maybe it's the same board?

Plugging in the charger, PWR LED comes ON only for a couple of seconds, but no fan-spin and no POST.
If I press the power button, all major voltages seem to appear again for two seconds... well, all except +VCC_CORE and +VCC_GT.
When it's on, I also noticed some PWM waveform present at PU1000 pin 30 (PWM_VSA), and thus +VCC_SA is generated briefly and it stays on during those 2 seconds.
However, I could not find similar PWM signals on pins 22 (PWM_IA), and 12-13 (PWM1_GT, PWM2_GT) which (I guess) should be generated by the same PU1000 chip for +VCC_CORE and +VCC_GT to start. Instead, they seem to go up flat to 1V for 2 seconds, until maybe some protection shuts down the board.

In my case, the board is ver. 3.0 and I noticed some differences between the board itself and the ver. 1.0 schematic available in here, namely the buck regulators for the +VCC_EDRAM and +VCC_EOPIO voltages described on page 57 (around PU1500 and PU1501) completely missing form the board (not factory-installed). I could not find neither schematic, nor boardview for this newer version, so at this point I have yet no idea how those voltages are (if even) generated...


@ytsoc, did you find anything else after replacing PU1000?
Did you managed to fix it after all?
Thx.

[marcelofct]

Re: XPS 13 9360 no CPU power

i have the same issue eith a dell 9350 turn on and turn off after 2 sec

[dune6170374]

Re: XPS 13 9360 no CPU power

Same for me XPS 13 9360 LAD841P Rev 3.0 I guess on component is weak on this series but which one