ASUS GL752VM not turn on

[djmixledj]

Hello,

I have an ASUS laptop that no longer turns on when I press the power button yet 3 lights are present when the charger is plugged in (power button, airplane mode and shift)

Thanks to the forum I got the diagrams. I took measurements with the multimeter but I can't identify the problem.

I have the impression that ALL_SYSTEM_PWRGD is the problem.

On leg 68 I measure 199.4 on the voltmeter



I don't understand why such a high value?

Is the chip broken?

can you help me please?

[mon2]

ALL_SYSTEM_PWRGD

This signal should be a logic '1' and assuming it will be ~3 volts only if each and every power rail on the board is considered to be within the proper voltage range. Otherwise this signal will remain logic low = '0'.

Noting the above, suggest to power down. Meter in resistance mode. Measure the resistance to ground of each and every inductor on the board. Each such inductor is linked to a switching power supply power rail. Report any low resistance measurements which may indicate a shorted part on that rail. By design, low voltage power rails will be with a low resistance to ground so they can be excluded as a suspect but post your list of measurements in ohms.

Often, the fault is in the DCin mosfets & charger IC region.

Suggest to review the charging circuits sticky by piernov - see above. Has a wealth of knowledge on the topic.

[djmixledj]

Thanks for your answer !

if I don't say something stupid PU8901 is charger IC

the first one I tried gives me an increasing value until 200
The second gives me 0.610

[mon2]

PU8901 sounds familiar but share the topside markings of the IC. Often it will be the Texas Instruments BQ series or Intersil (now Renesas) ISL series. Even better if you post a clear pic of the IC for verification. With regret, Asus schematics are well protected. Guessing their staff will be subject to a hurting in their dungeons if anyone leaks out the schematics.

[djmixledj]

[mon2]

Indeed, this is the charger IC.

Search for 'BQ24780S' to study the pinout / datasheet / reference schematics.

This charger IC likes to operate with N-channel mosfets (2 of them for DCin power path).

If you have fine tipped meter probes, suggest to monitor the voltage to ground of a few pins on this charger IC. If the meter probes are not fine tipped enough, then suggest to not do the voltage checks since the probes may short multiple pins and kill something else.

The game plan is to locate the ACDRV pin on this charger IC -> locate the 4k smd resistor to find the 2 x DCin mosfets that will be nearby. These mosfets need to be measured using only resistance mode on your meter. No power to the board during this resistance check. From the resistance checks, we can confirm if the mosfet(s) are defective for this logic board. Often, the fault is in this region of the board.

BQ24780S data page:

https://www.ti.com/product/BQ24780S?...B&gclsrc=aw.ds

[djmixledj]

Yes i have fine tipped meter probes
the ACDRV pin with power gives me 24,8v

I will try to locate 4k smd resistor to find the 2 x DCin mosfets

If Mosfet is defective what value would i have with the multimeter ?

[mon2]

Good. Suggest the following:

1) The ACDRV is a good voltage. The expected voltage is ~25v which you have. This may allow us to assume that the DCin mosfets are OK but let us confirm.

2) Remove all power. Meter in resistance mode to measure k ohms. Place one meter probe onto the ACDRV pin on the charger IC. The other meter probe onto pin # 4 = GATE of any nearby mosfet. When you find a resistance of ~4k ohms, you have then found one of the two DCin mosfets. Locate the other and report their topside markings. From these markings -> search for their datasheet for the pinout.

3) In resistance mode, measure:

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

of each of these DCin mosfets. If any of the checks are not hundreds of k ohms then that mosfet may be defective. Post your mosfet measurements. NO power to the board during resistance checks - only power to the people.

[mcplslg123]

No point probing the charging circuit if ACDRV is 25V. Its fine. Move ahead.Your problem lies elsewhere.

You have concluded on your own,All sys pwr Good is the issue.

Proceed and share your readings as suggested in post#2 by mon2

[djmixledj]

Thanks for your help !

In resistance mode i select M because k gives OL. while M i have :

Meter probe onto the ACDRV pin on the charger IC and the other meter probe onto pin # 4 gives1.200 on the first Mosfet and 1,450 on the second Mosfet




For this test :

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

I put probe meter on source and the other probe on drain ?

[mon2]

Correct. No power to the board during resistance checks. Meter in resistance mode. Pick any pin from 1-2-3 (they are shorted together on the mosfet) and another free pin on 5-6-7-8. Post each measurement.

[djmixledj]

--- Mosfet 1 ---

source (1-2-3) & drain (5-6-7-8) = 0.230
source (1-2-3) & gate (4) = 0.204
gate (4) & drain (5-6-7-8) = 0.437


--- Mosfet 2 ---

source (1-2-3) & drain (5-6-7-8) = starts at 0.80 and increase if I stay pressed until 0.250
source (1-2-3) & gate (4) = 0.219
gate (4) & drain (5-6-7-8) = 0.430

[mon2]

Do not worry about these mosfets at this time.

Can you link the schematics for this board? Could not find it in my database. Post only the link if the schematic is inside the schematics sub-forum. Outside links will be banned.

The next step is to remove all power. Meter in resistance mode (not diode mode). Place one meter probe onto an inductor (either color) and other meter probe to ground. Perform this check on each inductor. This is because each inductor is linked to a switching power supply (turns on/off for better efficiency). If there is a low resistance on a power rail, the power supply will shut off.

Respectively, this will lead to the ALL_SYSTEM_PWRGD to remain at logic low.

[djmixledj]

Boardview : https://www.badcaps.net/filedata/fetch?id=2010916
Repair guide : https://www.badcaps.net/filedata/fetch?id=2010917

[djmixledj]

I have the impression that the DCin mosfets are on the other side of the card

[djmixledj]

I carried out the measurements on the two mosfets in the photos above


--- Mosfet 1 ---

source (1-2-3) & drain (5-6-7-8) = 1.115 M
source (1-2-3) & gate (4) = 8.05 k
gate (4) & drain (5-6-7-8) = 0.900 M


--- Mosfet 2 ---

source (1-2-3) & drain (5-6-7-8) = 1.120 M
source (1-2-3) & gate (4) = 8.05 k
gate (4) & drain (5-6-7-8) = 1.108 M

[djmixledj]

Do not worry about these mosfets at this time.

Can you link the schematics for this board? Could not find it in my database. Post only the link if the schematic is inside the schematics sub-forum. Outside links will be banned.

The next step is to remove all power. Meter in resistance mode (not diode mode). Place one meter probe onto an inductor (either color) and other meter probe to ground. Perform this check on each inductor. This is because each inductor is linked to a switching power supply (turns on/off for better efficiency). If there is a low resistance on a power rail, the power supply will shut off.

Respectively, this will lead to the ALL_SYSTEM_PWRGD to remain at logic low.

The first one at the top : the value goes up to 200 K and eventually shows OL then it continues and shows 1,500 M and the value goes down to show OL
the second below : the value is 0.569

[mcplslg123]

I repeat, your problem is not in charging area.
Measure resistance to GND on all big coils to begin with.

With asus , powergood signal is often the issue-so start checking each and every powergood signal.

All system power good will rise only if all powergood signals are present. If you've any missing powergood signal,allsys pwr good will be pulled down.