Asus Zenbook 15 UX563FD 20v on first Mosfet D no power not loading

[dbuergi]

Hi all,

i have this board revision which is not doing anything. The only part on the board getting 30c warm is the 822 resistor on the top left (i hope it's alkso visible with the reflection). On the side to the BQ chip it shows 20v to ground and on the other side 0,7v.
What i also did until now:
-removed the dc fets and changed them even if removed measurements where fine.
-replaced the BQ24780S with a brand new one (pin 6 ACDET shows only 1,7v and this should be my problem since it is dragged down).
-pin 6 shows 19k ohm and i found the other resistors which go to pin 6 (marked them red and they all show also 19k ohm on this side).

So any ideas where to look next or what to check? Is there any available boardview for other comparable models?

[mon2]

From another but similar schematic for Asus. Compare against your board for the high side resistor @ PR8904.









Remove all power. Meter in resistance mode. Measure the resistance to ground of drain pin on PQ8902. What is the resistance? We are checking if the main power rail is shorted.

The ACDET voltage is too low. Is the power adapter the original and proper adapter for this Asus model? If not, there will be an expected voltage drop. This can lead to a lower ACDET voltage. If the power adapter is stable @ 19-20V then investigate the high side resistor value @ PR8904. Does the resistance match the schematic value? Usually this threshold needs to be 2v4 or higher to trigger the ACDRV pin = adapter_voltage + REGN voltage = ~25v.

[dbuergi]

From another but similar schematic for Asus. Compare against your board for the high side resistor @ PR8904.

Remove all power. Meter in resistance mode. Measure the resistance to ground of drain pin on PQ8902. What is the resistance? We are checking if the main power rail is shorted.

The ACDET voltage is too low. Is the power adapter the original and proper adapter for this Asus model? If not, there will be an expected voltage drop. This can lead to a lower ACDET voltage. If the power adapter is stable @ 19-20V then investigate the high side resistor value @ PR8904. Does the resistance match the schematic value? Usually this threshold needs to be 2v4 or higher to trigger the ACDRV pin = adapter_voltage + REGN voltage = ~25v.

Hello mon2,

It's the original charger for this board.
PQ8902 only shows 2ohm on D but with voltage injection (1,2v and 2a) it draws 1,2v and 0,6a and GPU gets warm.
Diode mode on mosfets:
8901: 0,49v and 2,2v
8901: 0,49v and 1,3v
Removed they show normal values with OL.

Back to the BQ area, i got my macro lens out to make a better picture. BTW REGN is 6v.


On the right side i have three resistors which have one pin connected to ACDET i marked them with 6.
In ohms mode one has 19k ohm (bottom left)and the others 10k (top) and 47k (bottom right).
In this area i have 1,7v.

Next to the 822 i removed a resistor which showed 130k onboard but outside 300k so it should be faulty.

[mon2]

The 130k resistor does not look to be linked to the ACDET pin on the charger pin #6. Confirm by using DIODE mode setting on your meter. No power to the board. Touch the meter probes to hear a tone beep.

One meter probe on pin #6 (ACDET) on the charger IC; other probe on either side of this 130k resistor pad. If you do not hear a tone beep, then this part is not linked to the ACDET pin and should be placed back as before.

Repeat this probing to find the true high side and low side resistors mating with pin #6 of the charger IC.

[dbuergi]

I check again. As posted the three resistors marked with 6 are connected to pin 6 and somehow i missed that the resistor above 822 on top left is also connected to pin 6.
It shows 47k in ohms mode and with connected charger 1,7v on side connected to pin 6 and 20v on the other side.
The 20v side is also connected to 822 resistor and the 130k resistor which showed 300k removed from board.

[mon2]

Use an online resistor based voltage divider calculator to adjust the high side and low side resistors (as required) to output a 2v4 voltage for pin #6. That is, you will have to dial down the high side resistance so that the ACDET voltage increases. Double check the resistor values before proceeding.

[dbuergi]

Use an online resistor based voltage divider calculator to adjust the high side and low side resistors (as required) to output a 2v4 voltage for pin #6. That is, you will have to dial down the high side resistance so that the ACDET voltage increases. Double check the resistor values before proceeding.

Sorry it took some more reading to get everything right, im still learning.
I removed the high side resistor and it shows 127k and my low side removed 20k so calculated it should be around 2,7v and fine. The resistors are not my problem any longer and something else is dragging down here?

[dbuergi]

I forgot to mention that 43T next to the 10 Ohm resistor should be the BAT54CW from your second pic. Diode mode shows normal values. I also changed my high and low side resistor with same values (high 127k and low 20k). I`m coming out at 2,7v or is the tolerance too big with 0,3v and needs to be adjusted? Normally between 2,4 and 3,1v should be fine.
I marked everything in the picture. Any other ideas?

[mon2]

Good on the new ACDET voltage. This range is now OK. Carefully, measure and post the voltage on each pin of this charger IC in a table for a review. Be sure to include the pin # and their function else it is more difficult to compare against a known good charger IC.

[dbuergi]

Good on the new ACDET voltage. This range is now OK. Carefully, measure and post the voltage on each pin of this charger IC in a table for a review. Be sure to include the pin # and their function else it is more difficult to compare against a known good charger IC.

Ah sorry my description was bad. I meant 2,7v with the calculator and my replaced resistors. Problem still is the same with 1,7v on pin 6. :-/

[mon2]

Oh Measure the resistance to ground of ACDET pin. No power to the board during this test. What is the exact resistance at this time?

[dbuergi]

Oh Measure the resistance to ground of ACDET pin. No power to the board during this test. What is the exact resistance at this time?

19k Ohm

[dbuergi]

Oh Measure the resistance to ground of ACDET pin. No power to the board during this test. What is the exact resistance at this time?

Okay maybe i got the right twist now. Since i have 20v and 0,7v on the 822 resistor something is dragging down on the other side and this point goes to the battery area.
The diode on my pic shows voltages in every direction and i have a e7ej tantalum cap (not tue one one my pic) next to the battery connector which is the only one one the Board with no continuity. So could this be the cause?
Any information about the precise specs for the diode?

[dbuergi]

Okay maybe i got the right twist now. Since i have 20v and 0,7v on the 822 resistor something is dragging down on the other side and this point goes to the battery area.
The diode on my pic shows voltages in every direction and i have a e7ej tantalum cap (not tue one one my pic) next to the battery connector which is the only one one the Board with no continuity. So could this be the cause?
Any information about the precise specs for the diode?

Finally some news. I unsoldered the JB2 ?diode? and finally got my 2,7v on pin 6 back.
But! the board is still not working. At the moment i can see that the first DC mosfets tries to switch and stops and does this in a loop. My guess is that it could be a reverse protection diode or p channel mosfet and without it there is no final go. So any ideas on this theorie and maybe anybody can help with replacement identification?
Also second mosfet (was also replaced to test if behaviour changes) is still showing 0,49v and 1,3v and has 2 Ohm on source. But it's connected to system rails and voltage injection didn't show any shorts.

[dbuergi]

Oh Measure the resistance to ground of ACDET pin. No power to the board during this test. What is the exact resistance at this time?

Hello mon2,

maybe you have any more hints or ideas? I replaced the JB2 which is a BAV99W but the behaviour went back to my 1,7v and no more pulsing on first fet. :-/

[mon2]

Suggest to place back the original JB2 diode. Not clear on the full details of this JB2 diode and also the internal orientation of the potential dual diodes. That, if this part is with dual diodes, the anode to cathode placement inside will matter.

With the original JB2 diode, do you have 2v7? Also, remove all power -> meter in diode mode. Where does the single pin on this JB2 diode travel to on the board?

[dbuergi]

Suggest to place back the original JB2 diode. Not clear on the full details of this JB2 diode and also the internal orientation of the potential dual diodes. That, if this part is with dual diodes, the anode to cathode placement inside will matter.

With the original JB2 diode, do you have 2v7? Also, remove all power -> meter in diode mode. Where does the single pin on this JB2 diode travel to on the board?

No i only get 2,74v with the diode removed. With the diode i get 1,7v and 20v on drain of first DC mosfet. Removed i get 2,74v and the mosfet is pulsing under the thermal cam but there is not anything getting through it. Single pin has 4v and goes to the 822 resistor(one side 4v and other 20v).
I also made some more measurements on the BQ chip:
VCC 20v
ACDRV 0v
ACOK 0v
ACDET 2,74v
REGN 6v
CMPIN 0,3v
BATSRC 0,5-0,7v pulsing
BATDRV 0,155v
BATSRC 0,155v
SRV 0,155v
CMSRV 0-0,54v pulsing

Top right pin of the diode also shows 0,155v when it's on the board and 0v when removed.
So maybe my problem is somewhere in the battery path? Or maybe since CMPIN is too low the fault is somewhere in ACP /ACN/Shunt?

[mon2]

Yes. What is the resistance to ground of ACN? ACP? This is the main power rail. Testing if it is shorted.

Also the ACDRV voltage should be ~25v to enable so the dcin mosfets are also suspects. If the main power rail is not shorted then the dcin mosfets are to be tested with resistance mode to confirm they are not leaking.

[dbuergi]

Yes. What is the resistance to ground of ACN? ACP? This is the main power rail. Testing if it is shorted.

Also the ACDRV voltage should be ~25v to enable so the dcin mosfets are also suspects. If the main power rail is not shorted then the dcin mosfets are to be tested with resistance mode to confirm they are not leaking.

Sorry, was a bit busy but now have time to work on this board again.
ACN 8Ohm
ACP 8Ohm

I removed both mosfets from the board and they work normal and show no strange behaviour. Onboard i only get 6 MOhm. With second mosfet removed i get 20v on drain and source of first fet. When both are onboard only 20v on drain of first and nothing else.

[mon2]

ACN 8Ohm
ACP 8Ohm

If these are resistance values to ground then the main power rail is shorted. Test the resistance to ground of each and every inductor on the board. Confirm if you see a similar measurement near the CPU.