Asus Zenbook DUO UX481F – small water damage and thermal paste

[corrize]

Hello, the laptop has a resistor cdamaged by water and dead (open line) close the charging chip. I will replace it soon.
I found a lot of thermal paste on coils and componets close CPU.
With meter, I saw 2,6 Ohms between ground and shunt resistor close power jack. So I guess it's too low.
I don't find true short (0 Ohms) on the board, no coil shorted.
I don't found bad mosfet (shorted drain-source). I found 2,6 Ohms to the « output » of the second mosfet close power jack.
I found a coil (close CPU) at 2,6 Ohms.
I measured between the output of 2sd mosfet (2,6 Ohms) and the CPU coil (2,6 Ohms), and I found 0 Ohms. So I guess something is shorted on this line. Right ?
il devrait y avoir un convertisseur de tension from 19v to CPU voltage ? And I'm scared the 19v may has reach the cpu.
Probably not yet needed, but here the schematic of UX481FL (that should be the same).
https://www.badcaps.net/forum/attach...0&d=1644878048

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Update :
I found a second coil close CPU at 2,6 Ohms

To summarize, the output for 2sd mosfet (high side, close power jack) is directly linked (biping, 0 Ohms) to 2 CPU coils. So 19v rail is directly linked to CPU. I guess there is an issue on this line. Right ?

To put it another way ; this output of 2sd high side mosfet is 2,6 Ohms to ground. I guess it’s the CPU internal resistance.
I guess something in this line is dead. Right or not pls ?

On this line, there is these 2 CPU coils so, associated to 2 MP86905. I don’t understand what is it ? Buck convertor or regulator ? I don’t thinks the twice are dead. But I don’t know how to test them. Measures compared seem to be the same.
Whar else ? Do you see wich component could be dead on this line pls ?

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Update : confirmed, there is something bad around this chips.

According to datasheet (in attachment) of MP8690, there is a « IN » and « OUT » (see schematic, and photo below, components are at the same place). I measured between in and out : 0 Ohms, for the 2 chips close CPU.
I found 2 other same chips on the board (same configuration, close coils) and there is a resistance between in and out.

So, something is fautly for the 2 chips close CPU.

But I can't believe the 2 chips are dead, with the same issue. I wonder if another component could be faulty and has effect on these 2 chips ? Any idéa pls ?

I know I could desoldering for check but it's an expensive laptop, I prefer spend time for diag. And solder as little as possible.

[reformatt]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

I surmise you are saying you have 2 ohms to ground on the +19V rail? You indicate the driver for the CPU buck converter is also shorted.

Liquid usually interferes with the feedback and/or the PWM for the converter resulting in MOSFET destruction, and the CPU/PCH/GPU cops the full rail (at least till protection kicks in). Its usually fatal but I have seen some designs survive this if the protection mode of the power supply is quick enough, but that is rare.

Both drivers being shorted isn't unusual BTW with liquid damage if the source of the PWM is what was affected.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Ok,exactly that I didn't want to read.
Anyway, when the diag come so close to the CPU… that smell not good for it. I still hoping a little bit because there is no short on CPU. I measured 2,6 Ohms on the caps under it, but no true chort. I will try to replace the chips, and see. I will update you.
Thanks for the share.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Another issue…
I desoldered the 2 chips and ok, the little « short » (2,6 Ohms) is gone. So, this part is solved.

Now, I measure 127 Ohms between ground and the out of 2sd high side mosfet (in place of 2,6 Ohms before I remove 2 chips). I guess it’s too low.
Probably one mosfet (or the twice) is dead. But I can’t understand what I read on the meter.

In resistance mode, between drain-source : 60 KOhms (1st mosfet) and 3,5 MOhms (for the 2sd)
So, my first think was the two mosfet have an issue (leak)
But in diode mode (not the beep mode) : I measure 0,5v in a direction, and after inverting the probes : 3v for the 1st) and (3v for the 2sd).
So, 0,5v seems indicate the junctions are goods ? And finally, I don’t know how to measure the mosfet onboard.

I need help pls ?

Edit : complete mesures in resistance mode :
Drain 1st mosfet to drain 2sd mosfet : 90K Ohms

Mosfet 1
DS : 3M
DG 1.3M
SG 3M
Mosfet 2
DS : 5K
GD : 1.2M
GS : 3M

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Up pls ?
I will probably desolder these 2 high side mosfet for check. Just because I can’t beleave the 2 chips close CPU (buck convertor) could be dead (shorted) and these high side mosfet still go
And I can’t trust the measures on these mosfet because the small liquid damage is beside the charging chip.
Can you deduce with the last measurments if the mosfets are dead or not pls ? I can’t do it.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Update : (for the previous issue, see the post of reformatt above).
I replaced the dead dual mosfet close the CPU, the short on main power rail is gone but le laptop don't start (maybe another issue)…

When I plug the charger, I have now LED light on power on button (blinking slowly 3s, maybe that indicate standby/sleep state ?) And when I press the button, nothing obvious happen (maybe a little change on blinking led but not sure). The LED keep blinking.

Battery charging, the battery LED blinking when the battery is unplugged, and stop blinking when it is plugged. So the charging chip seems working but I have doubt because a voltage (HIDRV seems to high, see below) and because there was oxydation close and component linked to, destroyed by oxydation.

On another coils, I measured 3,43v and 5v, so the 3.3v and 5v are presents. (Maybe 3.43v is too high ?)
I don't know what to diagnose after ? If the charging chip is ok, that could be a super IO issue. Any idea pls ? I have schematics but no boardview.
------------------
Battery measurments :
When I press the power button, the power led keep blinking (charger or battery plugged, or twice).
Battery plugged : 17v at the coil close the battery connector and the charging chip is hot (50-60 degree) but not burning. Maybe normal because it's a 15v battery.
Battery unplugged : 8,4v (seems too high)
Below, voltages on easy access, tell me if another can be usefull pls ?

Charging IC ¬(BQ24780) - (battery unplugged)
1 - ACN : ?
2 - ACP : 19.4v
3 - CMSRC : 18.8v
4 - ACDRV : 24.3v
5 – ACOK : 6v
6 – ACDET : 2.6v
7 – IADP : ?

8 – DCHG : 0v
9 – PMON : ?
10 – PROCHOT : ?
11 – SDA : ?
12 – SCL : ?
13 – CMPIN : ?
14 - CMPOUT : ?

15 – BATPRES : ?
16 – TB_STAT : 0,3v
17 – BATSRC : ?
18 – BATDRV : ?
19 - SRN : 8.39v
20 – SRP : 8.39v
21 –ILIM :1.1v

22 - GND : 0v
23 - LODRV : ?
24 - REGN : 6v
25 - BTST : 5.9v
26 - HIDRV : 8.4v
27 : PHASE : 0v
28 : VCC : 19.4v

[mcplslg123]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

The voltage measurement you have given are all correct. Why you have put ? mark on so many pins?? Are they not present?? If by ? mark you mean not present, then you need to check SDA/SCL line. this is the SMBUS line thru which battery communicates with charging chip and SIO. this rail must be working. SDA/SCL uses pullup and the source of pullup is usually 3V LDO.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Thanks for answer, measures completed, PROCHOT is weird
Charging IC ¬(BQ24780) - (battery unplugged)
1 - ACN : 19v
2 - ACP : 19.4v
3 - CMSRC : 18.8v
4 - ACDRV : 24.3v
5 – ACOK : 6v
6 – ACDET : 2.6v
7 – IADP : 0v

8 – DCHG : 0v
9 – PMON : 0v
10 – PROCHOT : 0v-2.5v-0v-2.5v… (contiuously varies)
11 – SDA : 3.26v
12 – SCL : 3.27v
13 – CMPIN : 0.17v
14 - CMPOUT : 6v

15 – BATPRES : 0v
16 – TB_STAT : 0,3v
17 – BATSRC : 0.19v
18 – BATDRV : 0.23v
19 - SRN : 8.39v
20 – SRP : 8.39v
21 –ILIM :1.1v

22 - GND : 0v
23 - LODRV : 0v
24 - REGN : 6v
25 - BTST : 5.9v
26 - HIDRV : 8.4v
27 : PHASE : 0v
28 : VCC : 19.4v

Edit : I will measure later, today, if with battery only PROCHOT is stable. It should be 5v I saw.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

I checked new, PROCHOT and TBSTAT are « blinking » with start of blink synchronized with power LED.
I noticed TBSTAT is linked with the resistor in oxydation damaged zone.
The twice seems output signals generated and sent by the charging chip (according datasheet above), can I deduce the chip is dead ? Thanks to give your advice pls, it's a big job for me to replace a qfn-28.

Charging IC - (BQ24780) - (battery unplugged, except if indicated)

1 - ACN : 19v
2 - ACP : 19.4v
3 - CMSRC : 18.8v
4 - ACDRV : 24.3v
5 - ACOK : 6v
6 - ACDET : 2.6v
7 - IADP : 0v

8 - DCHG : 0v
9 - PMON : 0v
10 - PROCHOT : 0v-3.5v (contiuously varies) – batt plugged or not
11 - SDA : 3.26v
12 - SCL : 3.27v
13 - CMPIN : 0.17v
14 - CMPOUT : 6v

15 - BATPRES : 0v
16 - TB_STAT : 0v-3.5v (contiuously varies) – batt plugged or not
17 - BATSRC : 0.19v
18 - BATDRV : 0.23v
19 - SRN : 8.39v
20 - SRP : 8.39v
21 - ILIM :1.1v

22 - GND : 0v
23 - LODRV : 0v
24 - REGN : 6v
25 - BTST : 5.9v
26 - HIDRV : 8.4v
27 - PHASE : 0v
28 - VCC : 19.4v

[Sephir0th]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

17V at the coil related to charging but 8V at SRN and SRP. A most likely dead CPU and a new issue every time you touch the board.

This neither sounds like trustful measurements nor that the board could be fixed, which is a pretty bad start here.

We need to know how far the board goes in the sequence after pressing the power button. So anything more than 3.3V and 5V present?

[mcplslg123]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

PROCHOT pin has no role in S5 stage and will come into play in S0 stage-so ignore this. Your charging IC measurements are more or less ok. Perhaps fault lies elsewhere.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

I checked the voltage coils present

CHARGER PLUGGED ONLY (NO BATTERY)
3.3v
5v
1.83 probably +1.8VSUS
1.06 probably +1.05VSUS OR/AND +VCCSA ? (above PCH)
battery coil : 0.17v (and 16.29v when only battery plugged, for 15v battery)
All other 0v

I checked the RAM power chip ; almost all voltages at pins are blinking and it don't provide 1.2v
I have doubts about the charging chip, because it's one of the mains « always on » power « providers ». And because there is no blinking signal before (in input) this chip, but two output are blinking : PROCHOT and TB_STAT. In the datasheet, these signals are shown as output. So if all input voltages are stables and outputs are blinking, the chip should be faulty ? (I ordered new chip for replace and check).

BUT, there is something else very very very strange :

WITH BATTERY PLUGGED ONLY :
at power off, no sign of life, no LED, nothing blinking, with meter at coils : only one has voltage : 16.2v (battery), no 3.3v, no 5v and nothing else.
And when I press the power button, the latpop start instantly to blink. So the power button « works » (so without 3.3v and 5v ??)
At this blinking state, I measured coils : at the 5v coil : nothing, and at 3.3v coil, I have 5v !
(On this board, it seems there is no 3.3v-5v chip, probably they are separated).
I don't understand how to such behavior is possible ?

[Sephir0th]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

In modern platforms it is absolutely normal to have the ALW voltages "sleeping" in battery mode. The EC, which is responsible for pulling up the Power switch, does get supplied by another 3.3V power rail (without coil present) in 99% of the cases.

Personally i think there is no point to assume a issue in the charging circuit since 3.3V, 5V and even 1.05V come up. Ordering a replacement will be just a waste of money and of time. My guess is there is simply the OVP triggered and the charging controller let the main power rail pulsing for this reason to save the board from further damage. Possibly a (partial) short to GND at one of the power rails which have to come up in the late sequence. Resistance to GND measurements are possibly the key here.

My honest opinion for this case in relation to your chip-level experience: Get rid of it or Hand it over to a reputable repair Shop.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

The laptop has a new behaviour : now, no more 3v 5v (finally I found the 3.3v-5v chip) and when I plug the charger and press power button, nothing happen, the charging chip seems dying slowly. I will replace it soon and see.

Edit
Sorry, didn't see your answer before posting. My first goal is not to fix it, what matters is the diagnosis, I find it fun. And if it is not repairable, it is to find the origin of the issue. I know what I'm doing, I check for too low resistances or short circuits before powering up and I don't do destructive tests. After that, if the super IO has a shorted line or the cpu is burned out… it happens.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Update : I replaced the charging chip and the same, except BATSRC and BATDRV : 8.38v instead 0.2v (without battery).
The laptop behaviour is nearly the same. The power light blinking...

I'm focused on something weird : there is a chip 5E= a step down controller at up-left on picture. This chip is usualy for power supply Ram memory but I guess not in this case. It close the chipset, and provide (via 2 mosfet) the second coil (up, left of the board on the picture) mesured at 1.06v stable.
The LGATE (track in red on picture) of this chip is unstable and blinking between 0.7v-2.5v, the UGATE too but in a little range of 0.03v.

It's weird because LGATE is an output and there is no other pin of this chip whith voltage unstable or blinking. How it is possible ?
Logically, if all inputs voltages are stables and the output voltage is unstable, the chip could have an issue ?
How can I check ?
The mosfet is good : it has resistor in MOhms gate-GND, gate-drain and gate-source.

[piernov]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Don't touch unrelated circuits, very likely to kill PCH if you mess with the buck converter for its core voltage.

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

I'm searching the cause of boot loop with measurments :

The PSU consomption : 10 – 100mA
I plugged an USB key and when the LED flashing very briefly, the boot loop restart instantly.

The 5 coils above chipset/CPU :
1 coil : 1.8v : stable
1 coil : 1.06v stable
1 coil : 0 to low voltage, but unstable
2 coils Vcore : 0v (don't try to start)

At coils of 3.3v 5v chip :
1 coil : 3.42v (stable)
1 coil : 5.18v (stable)

At coil of ram memory :
1 coil : 0 - 1.4v (unstable)

Battery coil : 0.2v (battery unplugged) but charge when battery plugged)

I measured some power good voltages but hard to find without boardview :
(with boot order number, see the last page of schematics, link above in this thread)
9 - 1.8VSUS_PWRGD : 3.3v stable
10 - 1.0VSUS_PWRGD : 3.19-3.22 unstable
15 - PWR_SW# : 3.25v stable (should be 3.3v ?)
22 - ALL_SYSTEM_PWRGD : 0 to 2.22v unstable (boot loop)
23 - IMVP8_PWRGD : 0v (need +VCCCORE)

What is it possible to deduce pls ? Super IO and PCH are good because they talk to each other ?
The boot sequence stop when the CPU is requested ? It don't respond (because it is not powered) ?
3.25v stable (PWR_SW#) is it too low at power button ?

[corrize]

Re: Asus Zenbook DUO UX481F – small water damage and thermal paste

Update : indeed, VCC core was missing, I found a bad solder on CPU mosfets. Now, solder is good, I checked on all pins.

New test : when I plug the charger (without battery), the chargin LED goes on, and next power LED on, it goes off after a few seconds.
I measured VCC core at coil, It grow up very briefly like all other coils voltages (pulse) at 0.8v, and goes to 0v. (So VCC core is « present » now, it was missing before).
So all other voltage, even the dedicated GPU have a same pulse (start to start).
At PSU : when I plug the charger : the voltage goes at 400mV two time (pulse) and 0v.
I measured IMVP8_PWRGD : there is now a pulse 1.7v (not present previously). But should be 3v and not 1.7v ?

So, yes, the CPU could be dead. But not shorted (3,6 Omhs, for I7-10510U). What can I measure now for confirm the CPU is dead pls ?