Dell XPS 13 9370 Laptop, No power, not charging

[rob_hen]

Hello!

This is my first post for help, and I am quite newer to board repair, so bear with me.

I have this board here (LA-E671P), with no power, and doesn't charge. No lights come on when plugged in.

After visual inspection of the board, U22 is obviously blown up. This is the for backlight, and there is no shorts present after removing the chip and replacing.

There is 3 USB C ports to power this board, USB 1 gives 20V, while 2 and 3 only give 5V.

My observations using USB 1 at 20V (0.075A draw on Ammeter, slowly drops from 0.136A)

PU101 gets very hot.
19.5V on input pin #1
9.65V on EN pin #4
0.675V on pin #5 +3V_LDOP
Resistance to ground looks normal, nothing is low.

+3V_LDO line reads 0.4V, but has 6ohms to ground.
+3V_ALW reads 0V, and has 59.5ohms to ground.

There is 20V going into PQ100 mosfet that takes power from the USB 1 port only, and 18.5V on the Gate.
However, there is no output of voltage after this point, measuring PQ101 Mosfet for the +CHG_VIN_20V gives 0V.
Resistances of mosfets to ground, and between gate source and drain are ok. Nothing low.

Holding down power button doesn't affect these measurements.

These measurements are with the battery disconnected.

Strangely, with the battery connected, things seem to half work, but still no power or charging.

Battery connected, no power adapter, and holding the power button:
+3V_LDO
+3V_ALW
+3V_VLP
+5V_ALW

No other voltage rails seem to be present or shorted.

Any ideas? Maybe I have a dead EC or PCH.

[mcplslg123]

+3V_LDO line reads 0.4V, but has 6ohms to ground.-This is where problem lies.

The resistance to GND here should be in Kohms. I beleive you measured resistance to GND without any power source connected.

You need to inject 1V/5A on +3V_LDO and see what's getting hot. Very likely it should be EC and/or PCH

[rob_hen]

Thanks for your reply mcplslg123. I have injected 1V on +3V_LDO, with no current draw. Going up to 1.1v, 1.2v, around 0.200A draw. I don't believe that is enough power to make lots of heat, please correct me if i am wrong.

PCH, EC, and other components not getting hot. Is it safe to up the voltage until something gets hot?

[mon2]

Review PU500.

Measure the voltage to ground of:

PL500
ENLDO_3V5V
+3VLP ; LDO rail
PL501

If any are at 0v -> remove all power and measure their resistance to ground.

Is the output pin #5 (+3V_LDOP) of PU101 still @ ~6R ohms to ground? No power to the board if checking the resistance.

[rob_hen]

Hey mon2, here are my measurements:

PL500 - 0V, 60omhs
ENLDO_3V5V 0.08V, 800k ohms
PL501 - 0V, 59.5k ohms

3V_LDOP, is in mega ohms.

3V_LDO (after transistor PQ126) still reads 6ohms

also I noticed resistor 508 and 509 reading weird (could be different because it’s in circuit)

R508 - 720k ohms (500k resistor)
R509 - 200k ohms (500k resistor)

thanks

[mon2]

PL500 - 0V, 60ohms

Flux and remove PL500. After this part is removed, test the resistance to ground on the PCB of the 2 pads used by this component. Which side is reporting to be 60 ohms to ground?

[rob_hen]

I mixed up the inductors and made a mistake here…

PL500 - 0.008V, 13M ohms

PL501 - 0V, 60ohms

[Sephir0th]

60 Ohms at PL501 is for sure something partial shorted and pretty much actually being the Chipset as the most likely origin. Voltage injection along with observation of thermal camera will tell for sure.

[rob_hen]

Sephir0th Agreed 60 ohms is way too low, but not direct short to ground. If using power supply to inject voltage, would need to dial up the voltage to make it accept any current right?

How much voltage and current do you suggest I set my power supply to, on PL501 with 60ohms?