DELL Latitude 5410 - dead; pwrbtn flashing

[YellowJacket]

Hi folks,
DELL Latitude 5410, board number FDZ41 LA-J371P Rev: 1.0 (A00), schematic uploaded in different post, here is the link --> https://www.badcaps.net/filedata/fetch?id=3484415

When I connect it to a power ( DELL round charger, or USB-C ), LED on the power button starts flashing white, and the laptop doesn't do anything ( flashing slows for a very brief time in time when I press it, but it continues again ). Battery is not charging. While the charger is connected, I have few voltages present, but some of them are fluctuating, see attached pictures.
All I was able to figure out, was following the timing diagram in schematic ( page 5 ), and I had no issue with any voltage rail, until I came to `PCH_RSMRST#` signal ( 7th signal ) and this was the first position, where the fluctuation appears. PCH_RSMRST is deployed by EC chip, so now I am not sure, if there is an issue in EC ( not likely ), or in PCH or somewhere else. Its resistance to gnd is 60k.
I would be really thankful for any hint, what to check now.

[mcplslg123]

The coil marked as 49K is the main power rail and should be 12-14V approx.It should be stable.

The reason you are getting fluctuations on RSMRST# pin is 'coz of fluctuation on this NVDC rail.

So look towards dc-in mosfets and charging area to make that coil voltage stable. Once you are able to fix that,it should start charging and may power on as well.

So going by the info provided by you, I'm almost sure your issue is in charging ciruit.

[YellowJacket]

Hi mcplslg123, you are indeed correct and I just figured it out yesterday, I didn't update the thread. I tried to measure both PQ700 and PQ701 dual channel mosfets out of the board, and they are good ( tested with diode mode both integrated transistors for each of G-S-D. They are opening and closing as they should ). Also tested the PQ702 mosfet for charging.
Measured values around the charging IC ( ISL9538CH ):
DCIN = 19V
VDD = VDDP = 5.16V
ACIN = 3.5V
ACOK = 3.1V

There are few waveforms measured around PQ701 ( attached pictures ), first two are input and output of PQ701, second two are gate signal of high side and low side of PQ701.

I suspect the ISL IC, even after watching this video --> https://youtu.be/yKwOsWSLTqg?t=2625 <-- quick recap = he actually had the same problem, with fluctuating main power rail. He swapped the charging IC ( also ISL9538CH ), with no change. But he had a short on one of power rails, what he didn't notice from the beginning. After fixing short, the board still acted the same, so he decided to swap the ISL again, and then board came alive. So looks like I am going to swap it too, and I will update this thread. If you have any suggestion though, before the IC arrives, let me know. Thanks so far.