GL702VM not charging/unable to power on

[Peter Toropov]

Disclaimer

This is my first time at attempting such repair and troubleshooting, so I apologize in advance if I do something wrong or misunderstand some things. I will attempt my best to research more information to better understand everything.


Issue

Laptop was unable to charge the battery, but was able to boot up without it, when powered on it had unstable CPU clocks while under load due to sudden throttling when reaching 70C. Upon visual inspection, a blown capacitor PCI8601 was discovered near MOSFET PQH8601, which has been replaced. The MOSFET itself, when checked for resistance shows 10.2kOhm resistance on pin P_DDR_DHR_30. On the other pins, P_DDR_LX_30 shows 120Ohm (unsure if this is relevant in any way). When the battery was connected to the board, it was unable to boot, but the power light came on.

In its current state, the laptop is unable to boot/charge and appears completely dysfunctional. The battery connector is shorted to ground, along with AC_BAT_SYS pins.


What has been done by this point:

While reading other posts, I discovered that replacing the charging IC, PU8900/SN2867RUYR/BQ24780S, might help. However, upon its replacement, nothing changed and everything seems to get worse.

After being unsure as to where to go next, I contacted mon2, who helped others with similar issues. He recommended creating this post and checking voltage and resistance on two DCin MOSFETS.


Voltage/resistance readouts I got

A/D_DOCK_IN MOSFET (PQ8901) jumping 0.4-2V, 0 resistance across all pins, suggesting that it is defective.
19V MOSFET (PQ8902), jumping 0-0.24V, 0 resistance, also suggesting it being defective.


Possible next steps

Will try to find replacement MOSFETs (from other boards laying around), check them and replace the dead ones on the board.

[mon2]

Hello again Peter. See attached.

1) Remove all power. Meter in resistance mode. Start with measuring the resistance to ground of the 2nd DCin mosfet (PQ8902). Need to review this to learn if the resistance on the main power rail is too low.

QM3058 has 8 pins (4 on each side). Common pinout with other 8 pin mosfets where pins 1-2-3 = SOURCE; 4 = Gate; 5-6-7-8 = DRAIN.

Check the resistance to ground on PQ8902 (5-6-7-8 - pick any of these). One meter probe here; other meter probe to ground (metal shield is ok). What is the measurement?

2) Next, still with no power. Measure the resistance across the DCin mosfets as follows:

PQ8901

source & drain
source & gate
gate & drain

Repeat for PQ8902.

Post each measurement along with the units of measure (ie. ohms; k ohms; etc.).

[Sephir0th]

You're saying, after replacing a capacitor, the laptop went from unstable to "dead" condition, including a shorted main power rail?

If so, hq pictures of this area please. I don't see any indication for a fault in the charging circuit tbh.

In my opinion something went horrible wrong during the task, or a PQH8601 which could have been damaged already, finally shorted out.

Is the RAM supply shorted too?

[Peter Toropov]

You're saying, after replacing a capacitor, the laptop went from unstable to "dead" condition, including a shorted main power rail?

If so, hq pictures of this area please. I don't see any indication for a fault in the charging circuit tbh.

In my opinion something went horrible wrong during the task, or a PQH8601 which could have been damaged already, finally shorted out.

Is the RAM supply shorted too?

No no, I have replaced the cap, and nothing changed, the board was not charging the battery and the laptop was able to start up from just the power supply. It was after I replaced the charging IC that things went somewhere they weren't before. One of the capacitor's pads was ripped off, so it is bridged with PQH8601 MOSFET, which has the same pin AC_BAT_SYS as the capacitor had.

Unsure how to check the RAM supply, both RAM slots were working before everything else "collapsed".


Attaching both pictures of the cap and the IC

[Peter Toropov]

Measuring with no power:

1. The resistance measured from pins 5-8 (drain) on PQ8902 19V MOSFET to GND is 0 Ohms

2. Measuring across the PQ8901 DC_IN MOSFET:

source-drain: 0 Ohm
source-gate: 0 Ohm
gate-drain: 0 Ohm

2.1 Across PQ8902 19V MOSFET:

source-drain: 4.6 mOhm
source-gate: 0 Ohm
gate-drain: 4.6 mOhm

[mcplslg123]

Replace PQ8901 and re measure the resistance to GND on pin5-8 of PQ8902.

[Peter Toropov]

I was unable to find any substitute MOSFETs on other boards, so just ordered some M3058, they will most likely arrive in ~2 weeks

[mon2]

Always good to find the original as a replacement but this is a jellybean mosfet. Locate any similar sized (physical) N-channel mosfet on your board and review the specs. It should be capable of 30V Source / Drain support. Peak current is a nice to have - TI has some really good mosfets for the task but your other donor boards should be close enough and located in the DCin area of the board.

[Peter Toropov]

I did find an Alpha&Omega AONS32306, which has similar specs for drain/gate voltages, but maximum currents are way lower, than the ones on QM3058. Do they not matter?

[mon2]

Those are peak currents. Something really wrong if peak currents are required. You can test the mosfet you have. The lower the Rds value the cooler it will run.

[Peter Toropov]

Alright, thank you for clarifying. I have replaced QM3058 PQ8901 DC_IN with AONS32306. Resistance readouts:

MOSFET-GND

5.2 mOhm

Across:

source-drain: 4 mOhm
source-gate: 3.9 mOhm
gate-drain: 1.435 mOhm

Should I now test with with power?

[FZG]

Is that a burned spot on the board just below the BQ chip?

[Peter Toropov]

I don't think so, looks more like flux residue that I was unable to wash off.

[mon2]

Use alcohol and allow it to sink into the flux. Then remove it with a Q-tip. We use the Costco pharmacy grade alcohol which works well for us. There is some really stinky stuff we have in the building which is used for the nasty flux that is caked on. Can smell it across the building when it is sprayed. But this heavier grade flux remover works on everything.

[Peter Toropov]

FZG, you are correct. It is a little burned, but the resistors still give proper readings of 20kOhm on the right and the left. The burn marks are most likely from me overheating the board when soldering the IC. Tried to get higher quality pictures, but they don't seem all that better.

[mon2]

Other than the concern for this burnt looking area, you should be ok to test again. The concern is that if there is any exposed copper underneath this resistor.

[Peter Toropov]

Got 20V at PQ8901 DC_IN when measured to GND and 20V on PQ8902 CHG_PATH when measured to DC_IN.

[mon2]

Sounds good. Confirm if the gate voltage on these mosfets (pin # 4) is ~25 volts.

[Peter Toropov]

PSU drops voltage to 0.3V and PQ8901 now has a short between source and drain...

New resistance measurements:

source-drain: 0 Ohm
source-gate: 256 Ohm
gate-drain: 260 Ohm
GND-drain: 5.1-5.3mOhm

[mcplslg123]

PQ8901 is shorted again. Seems charging IC needs replacement also. Better to remove PQ8901 and measure resistance to GND on all pins of charging IC(no power attached)