Zenbook UX334FL

[Seb33]

Hi there,

I recently bought a dead Asus zenbook UX434FLA (i7 10th gen, integrated graphics, 16Gb ram). The first Power MOSFET close to DC connector was shorted so I replaced it. I now have 19v present everywhere on the board but all coils at 0v.

Resistance to ground on all coils :

1.2v (PL8601) : 262
+VCCGT (PL8103) : 6.5
+VCCCORE (PL8102) : 5.2
+VCCCORE (PL8101) : 5.2
+VCCSA (PL8104) : 36
+1.05VSUS (PL8301): 49
+5VSUS (PL8703) : 3.4K
+1.8VSUS (PL8303) : 2K
+3VA_DSW (PL8704) : 2.7K
+P_CHG_LX30 (PL8901) : 15.6K


Once DC Adapter plugged in:
- Measures on PT8904 :
1. AD DOCK IN : 19.2V
2. P_CHG_ACMOS_S_20 : 19.2V
3. P_CHG_PATH_19V_SHAPE : 18.94V
4. +3VA : 0V
5. +5VSUS : 0V
6. +3VA_DSW : 0VUX334FL Rev 2.0.pdf

If my understanding is correct, ITE8225 commands required voltages from CPU, RAM, PCH power supply Mosfets. VCC from ITE8225 is 1.4mV, resistance to ground : 5.2Kohms

I'm running out of ideas for things to check. Perhaps someone can tell me what creates the +3VS required by the ITE8225 VCC ?

Thanks.

[mcplslg123]

Does 19V reaches CLR after 2 dc-in mosfets? What is the fate voltage of dc-in mosfets?
Next move to 3V/5V regulator IC and check whether you have 3V LDO/5V LDO present or not?
This 3V LDO will power the EC chip IT8225

[Seb33]

Thanks for your help ! I measured 18.94 at CLR, 0v at the output of 3V regulator and 5V regulator (DOWN CONVERTER ATK1658BGQUF). I do have 18.94V at every entry point of dual Mosfets on the board. I do not see any 3V LDO in schematics. On schematics, VCC pin of IT8225 is fed with +3VS

[mon2]

Study page 99 of the schematics to see who creates the +3VS rail. Also sheet 88 shows the power rail switch for the EC.

+3VS is based on PU8702 who creates +3VA_DSW and is switched through mosfet PQ8811.

[Seb33]

Thank you mon2, actually I noticed component RT8249CGQW on page 99, which seem to create +3VAO, +5VSUSO, +3VADSWO but I cannot find this component anywhere else in the document or in the board view.

I replaced PU8702 as the former one was blown. I controlled the new one for a short between VIN and BOOT but didn't find any. Do you know any other tests to be made to ensure this kind of dual mosfet is working properly ? I found some additionnal tests on Youtube but they require the mosfet to be desoldered form the board. I was curious about the EN Pin of this Mosfet but it's connected to SIO chip. This is were I get lost: if SIO doesn't have +3V on VCC, how can it enable +3V Mosfet ?

I will check PQ8811.

[Seb33]

So finally I decided to resolder the down converter PU8702 and now the board is getting close to work ! I have voltage on coils. Problem is that the power is turning on and off like every second. It's just like it's trying to turn on all components but something wrong is detected and the power supply is turned off, then trying again and again. I can see the cpu heating at 30°C. Any idea on what to check ? Thank you !

[MEGMANAPT]

So finally I decided to resolder the down converter PU8702 and now the board is getting close to work ! I have voltage on coils. Problem is that the power is turning on and off like every second. It's just like it's trying to turn on all components but something wrong is detected and the power supply is turned off, then trying again and again. I can see the cpu heating at 30°C. Any idea on what to check ? Thank you !

I have a dell laptop in the same situation. i presume its the PCH in my situation.

you can try to connect only with the fan connected and connect to a display by hdmi. to power on just short pin 5 and 6 from the connector to power on. and see it it will power off it self.

[Seb33]

Thank you but I can't expect the laptop to turn on or do anything when voltages are unstable when the board is on the test bench. I think I solved this issue as I previously replaced 1 shorted Mosfet on the CPU and at the time I think I messed up the solder. Something was wrong on this mosfet, plugging the adapter the IC would check if all tensions are good and find out something is wrong with this Mosfet then turn power off from the first AC Mosfet. I resoldered the Mosfet again properly, adding solder to padds and soldering flux. Now I have stable voltage. Leds are turning on when I plug the adapter. I just have to resolder a leg of the charging IC before powering on as i noticed BAT_PRES was missing when battery is plugged in (again, I previously replaced the charging IC and messed up the resoldering step...). I spent more time fixing my mistakes on this one but so interesting to learn how these components work together and how to diagnose properly. I will update this post to let you know if it boots or not, fingers crossed !

[Seb33]

Unfortunately I believe wether the PCH or CPU is dead. Coils are not shorted to ground when I measure resistance but I can't get a stable voltage when all coils are soldered. AC light blink twice then orange (battery light) blink once.

I thought that a dead CPU or PCH would have at least a coil shorted to ground.

Looking with a thermal camera I Can see the PCH dual MOSFET starting briefly (26°C, around 1.2v) then both CPU cores MOSFET turn on and off very quickly. All this sequence take less than 2 seconds and keep repeating. Any chance this could Come from a faulty SIO ?