HP EliteBook 850 G5 without signs of life

[tranquility]

hello, i have a problem with HP EliteBook 850 G5
shoring no signs of life. led near charging port and on/off button are off.
board it taking just a few mA..i think it was 10mA

i measured some things but i don´t find anything

the ACOK ? pin 24 FRWPG (pin 24) am ISL9538h is low with 0V
but i dont know why

i cant really understand what the mosfets in the pictures are doing for crazy things.
i measuered voltage on coils....but now on mosfets near the coils too and they all had more than 10v i think one was there with 8v or something....so i think the cooils would have voltage, if the mosfets there will eb triggered

bios has no voltage on it. but maybe this is normal i read ? it gets voltage if computer is turned on ?

hope somebody can help me

[mon2]

VSYS is the feedback pin for the main power rail to the logic board.

A partial datasheet is shown here:




The main power rail is not a valid voltage. Remove all power. Meter in resistance mode.

Measure the resistance to ground at VSYS on the charger IC which is the same as the main power rail. What is the resistance in ohms? This check is to confirm if there is a shorted part on the main power rail.

Once the main power rail is normal, this higher voltage will be used to create always on power rails including 3v3 and 5v0 - one of these rails will most likely be used to pull-up the open-collector ACOK signal. That is, the charger IC is receiving the adapter voltage but is unable to raise this ACOK signal to a logic high. Instead, the pin is floating and requires an external voltage to park this floating pin to a voltage level which is often from another regulator on the board. That regulator is not yet powered.

[tranquility]

pin 3 (vsys) to ground: 2,3 MOhm but keeps constantly slow falling while measuring hmmm

aren´t the mosfets doing crazy stuff ? but i don´t know whats normal there Lgate und Ugate !?

[mon2]

No short on the main power rail.

Remove all power. Meter in resistance mode. Test each mosfet linked to this NVDC charger IC starting with the 4 mosfets on the main power rail. Checking if any of these mosfets is leaking.

Measure:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. Each measurement should be hundreds of k ohms or higher else could be defective and must be replaced. Test each of the 4 mosfets (high / low side linked to the main power rail).

If you see a suspect, flux and carefully remove the mosfet off the board -> then allow the mosfet to cool down -> measure again while the mosfet is on your workbench. Are the measurements still low if removed off the board?

[tranquility]

i don´t know what happeneed but i get another reading now

i was wondering about the boot and phase values and searched for the capacitors....is this strange.

here are the updated readings ion the picture

the mosfets have crazy effects during measurement. some valueas are different if i change + and -

(random named)
nr1
S-D: 50 kOhm
S-G: 5 MOhm
G-D: 2 MOhm

nr2
S-D: 50 kOhm
S-G: 2 MOhm
G-D: 2 MOhm

nr3
S-D: 40kOhm
S-G: 6 MOhm / 3kOhm
G-D: 2MOhm / 70k Ohm

nr4
S-D: 8 kOhm / 220 kOhm
S-G: 2,5 MOhm
G-D: 45 kOhm

[mon2]

Each of the low resistance readings is of concern. Mosfets are inexpensive. Suggest to replace each. Share the part numbers on each of these mosfets.

If this is not a good option, flux and remove the first 2 DCin mosfets (high & low side) off the board. Keep track of each and their locations. Then confirm if the measurements are similar when they are off the board.

For example S-D should not be 50k ohms. If you have the tools, consider remove and test each of these mosfets off the board. Be careful to not disturb other nearby parts on the logic board. Kapton tape helps to keep tiny parts as-is.

[tranquility]

the boot1 voltage is crazy ?

it should be the same as Phase 1 ????
it is shorted to the next pin (Asgate) .....wtf

[tranquility]

WTF the capacitaor from boot1 measues at one side the realistic voltage of 4.7 between the mosfets. on the other side it has the strange 13Volts. then comes 0 orm resistor with 13 volts on each side an then the ISL chip
i think there is really a short of this side then ?

[mon2]

It is possible that one or more of the DCin mosfets is leaking and causing the measurements you are reading. Test the resistance with the mosfet off the board. If the measurements remain low then the moset(s) must be replaced. Then test again.

[tranquility]

can somebody help me with the schematic ?
pin 13 ASGATE of IS9548h is shortet to BOOT1
but i can´t find where ASGATE is connected to ?

i ordered the IS9548h and Mosfets AON6380. thes are the 4 ones

or do you mean the 2 before could be faulty too ? they seem to pass the input volatage perfectly... they are SM3335p

i think the ASGATE is wrong in my picture....got the picture from a youtube video ? in the datasheet its calld ADPS: Reverse output voltage feedback. Use a resistor divider externally to configure the reverse output voltage

where from get the first 2 mosfets on the board triggered ? found no link on the board

[tranquility]

okay, i think the short was maybe coming from my exzessive pointing with the multimeter needle.
today i changed the ISL9538H chip.- now i got 5v ldo there on pin 8 and 18 back

the freaky thing is..on BOOT1 i measure ~5v and BOOT2 ~4.7v
so to kill anny possibility...i just remoed the 4 MOSFETS. an it´s still there....where the hell is this voltage coming from ?

on another side i found the lenovo schematic....there is no other connection in it. i can´t see another connection on the board.

isl is changed.....or directly damaged again ? so that the voltage comes out of the isl chip ? i don´t get it....is this strange

[tranquility]

okay....i missunderstood the boot thing i learned that it is necessary for the gate switching circuit for the mosfets. so normal that there is this voltage.

phew...okay..i have no acok and the mosfets are not triggered for some reason. i ordered new ones...but they aren´t send till today. i will check the old ones now and then put them back to the board...

okay, i think the short was maybe coming from my exzessive pointing with the multimeter needle.
today i changed the ISL9538H chip.- now i got 5v ldo there on pin 8 and 18 back

can sbd help me with this mosfet ? i don´t understand what it is doing. 19v ond drain and gate. and spource 0.23v
doesnt make sense ? or is it some switching circuit to change between battery mode and dc in mode that i dont understand
green is the +19v path as i understand it to the from the 2 smaller input mosfets to the 4 mosfets with the coil

[tranquility]

i desoldered this guy.
wenn im testing everything is okay so far. but...with multimeter in diode mode im bringing it to ON positon. when i am then checking the drain and source....its first a short = good. but then the voltage increases. is this normal behavior from an p channel mosfet ? the n channel doesn´t show this behaviour to me i think ?
or is this a bad one...

[tranquility]

okay....i am actually wondering why my SDL/SDA on the IS9538H are 0V
in another thread here...sbd is measureing 3.3v which should be right

so maybe my sdl/sda bus is dead for any reason ?

i think i found a 3v3 regulator....i can measure it on some pins...but i don´t understand this component and can not find it anywhere
there are no 3.3v given to the coil !

don´t know where this voltage regulator i think is getting its comman from ?

there are a few of this components with different pin counts on the board. and the "under the body" pins are varying as you can see in the picture
i am talking about the black ones on the right side of each coil

[tranquility]

i assume that the pch is shortet ?

the bios has no voltage. chip has 3v
so i injected 1v 2A there...

the only thing which is getting warm is the PCH chip besides the cpu

does it 100% mean the pch is shorted ? or can it be a component on the "other side" of the pch which is shorted, so the current is goiung through the pch and heating it ?
but i don´t find another component getting warm with the thermal camera.....so i think pch dead ?

[mon2]

Yes, it appears to be the case.

With no power to the board, what is the resistance to ground of the missing 3v3 rail? This rail, as you noted, is powering the PCH and also the bios, etc.

[tranquility]

~0.25 ohms on ground which are my cables
~2.20 ohms on that coil

another coil around there has 0.25 Ohms...voltage injection there heats the pch also

[mon2]

2R2 to ground on the 3v3 rail? Yes, that is far too low. Wait on other comments but based on the fact that the PCH is heating up, this is a dead end case.

[tranquility]

i first thought theese coils are for the gpu and 2.5 ohms could be normal and searched for the error on other components

now i get a lot smarter