Dell Precision 5540 - LA-H33, EDP51 - ISL chip not starting

[Kamcio]

Hello everyone!
I'd like to make my first laptop repair and i bought a faulty Dell Precision 5540 with no power and no charging.
Motherboard is similar to some XPSes - LA-H331P and EDP51/EDB51. Boardview acquired from this forum.
I poked here and there - there are no shorts on any coils. Mosfet's PQ190X gates are not opening.
19v is present up to the ISL88378H chip and the entry of these mosfets... and then it's gone. All pins around the ISL chip are 0v or below 0.5v.
I've resoldered/replaced the chip couple of times, but it seems the issue to be somewhere else. Main battery is 0v when tested on the table, 0v when plugged to mobo alone and 9,5v when plugged to mobo, DC plugged in and 11v injected to battery+ connector. CMOS battery is 3v.
What else can I check? Thanks for any help

[mon2]

Found the matching schematic.

Remove all power. Meter in resistance mode.

Measure the resistance to ground of:

PQ1901 ; pins 5-6-7-8 (drain pins) - testing if the MAIN power rail is shorted or not

[Kamcio]

Thank You for reply!
PQ1901 drain to GND started from 50k ohms and was rising when probed longer.

[mon2]

No short on the main power rail. Suggest to carefully measure and post the voltages on the ISL88378H with their pin labels for a review.

interested in:

vcc ; to confirm the charger ic is being powered
acin ; threshold for the adapter voltage
acok ; status pin for the adapter voltage

if the above are ok then share other voltages on the charger ic.

[Kamcio]

VCC: I haven't found this particular name on my schematics. There are DCIN pin17 19v, VDD pin18 0v, VDDP pin8 0v, ADP 0.3v
ACIN: 3.59v
ACOK: 0.02v

[mon2]

Review if pr1903 is ok. If pcb trace or solder blob, confirm not broken.

Test the voltage to ground of PL1901 inductor. Either side is fine.

[Kamcio]

PR1903 - doesn't look like cracked, blown or discolored.
Resistances:
GND to SDC_IN pad -> 80k and rising
GND to ADP pad -> 600k const
Between 2 resistor pads - 500k and rising


PL1901 - no voltage at all on both sides

[mon2]

PR1903 should be ~0R ohms according to this schematic. This trace is defective and should be fixed with a wire. Can you post a pic of this PR1903 location? The schematic and your board are 100% matching?

Test the resistance to ground of PL1901 inductor. We are checking if perhaps one of the low side mosfets is defective which will then show a low resistance on this inductor.

[Kamcio]

Alright, I've replaced PR1903 with another 0ohm resistor. Haven't powered the board on yet.
Now for whatever reason PL1901 reads 6 ohms to ground. I had that before when I touched gates on either PQ1900 or PQ1902 with beep mode. Problably opened these mosfets since beep mode sends some voltage to gates, ahh.
Schematics looks like 100% matched, at least components around ISL.
Attached pic has 000 resistor which is PR1903 - directly connected to ADP pin in ISL on one side.

[mon2]

Be sure that the low side mosfets are present on the board. This important to dial down the high adapter voltage to a low voltage for the main power rail. Otherwise, the adapter voltage will travel to the main rail and cause damage. If this resistor is @ 0R then test again to see if there is voltage on the main power rail. If either of the low side mosfets are shorted then this will sink the main power rail voltage.

[Kamcio]

From what I understand, low side mosfets are PQ1903 and PQ1904 and they are opened respectively by LG1 and LG2. There is nothing on these gates.
But I have good news - after replacing 0ohm resistor, there are more voltages on the ISL chip -> in attachment.
I've also replaced 2.2ohm resistors PR1905 on BOOT1 and PR1914 on BOOT2 because they had megaohms instead.

[mon2]

What is the voltage to ground of the ACOK pin?

[Kamcio]

0v, unfortunately

[mon2]

What is the gate voltage on PQ1906?

[Kamcio]

0.80v

[mon2]

Measure the resistance across PR1911. It should be ~100k ohms. If ACOK is truly ok, this pull-up resistor must be present to park the floating output of ACOK to a logic '1'.

[Kamcio]

Around 70k ohms on board
100k with resistor pulled out from the board

[mon2]

Test the resistance across PR1908. There should be a voltage on each side of this resistor. Also measure the resistance to ground on each side of this part.

[Kamcio]

It has 5v on both sides. Both also shows ~80k ohm to ground. 10k Between pads. I see there should be 4.7 ohm.
I should have bought 0603 and 0402 cap and resistor set

[mon2]

You could probably replace with a jumper here for testing. Worse case, the charger IC will have to be replaced. Suspecting it is for in-rush current protection to place a 4R7 ohm resistor here.