ASUS ROG STRIX GL702VSK no power issue PQ8901, PQ8900?

[ub6ib969]

Hi,

working on a ASUS ROG STRIX GL702VSK 60NB0DZ0-MB1260 that does not power on. At the PQ8900 PIN2 (P_CHG_ACMOS_G_20) I am receiving 24.7V and PIN1 (P_CHG_ACMOS_S_20) 20V, however when I place the PQ8901 P_CHG_ACMOS_G_20 it drops 0V. I don't have the replacement mosfets ( N-MOSFET QM3058M6AC PRPAK5*6
UBIQ) however will any N-channel mosfet with similar parameters work ? I also found that PCI8703, PCI8701 are shorted. any help would be grateful.

[mon2]

Yes, the N-channel mosfets can be replaced by many others. Dig through your motherboard donor pile and share the details of the N-channel mosfets that should be in the power path from the DC power adapter connector to the charger IC.

The caps are not critical but should be present onboard that are shorting. They are 10 uf @ 25V or higher rated caps.

[ub6ib969]

PQ8901 - N-MOSFET QM3058M6AC PRPAK5*6
UBIQ
PQ8900 - N-MOSFET QM3058M6AC PRPAK5*6
UBIQ

Don't have the exact n-channel mosfet but I do have AON6382

[mon2]

Good enough. You can also get samples from TI.COM online store and TI makes some really beefy mosfets. Proceed to test with the AON6382 devices.

[ub6ib969]

when replaced with aon6382 PQ8900 has the correct measurements however when PQ8901 is placed volage drops to 0.41v.

[mon2]

The original mosfets onboard were QM3058M6AC ? (N-channel type)

Confirm that the orientation is the same as the original. Be sure that the soldering of the replacement parts are not reversed. Post a pic of the reworked areas.

Next, with no power to the board -> meter in resistance mode -> share the resistance to ground of PQ8901 where the voltage is 0v41. Need to check the resistance of this leg of the power path.

[ub6ib969]

yes the original were QM3058M6AC, i will provide a picture and measurement shortly. thank you for your help
AC_BAT_SYS contains a short.

[mon2]

Ouch. Hope it is a shorted cap but let us see your resistance check. The next logical step is to measure the resistance from this point to each and every inductor to confirm the high side mosfet is not leaky. The deadly mosfets are the ones on the CPU rail. Never any power during DIODE or RESISTANCE checks.

[ub6ib969]

PQ8901 = PIN 2 P_CHG_ACMOS_G_20 = 127.7K (@ 200K)

[mon2]

Was this resistor removed or reworked?

[ub6ib969]

reworked.

[mon2]

Flux and remove that solder blob at the end. I do not believe it should be there and most likely is causing your short condition. Even better to flux and remove this part to confirm how the pads should be soldered back onto the board. This current sense resistor is just before the use of the main power rail. If this is shorted, this will cause your adapter voltage to tank like you are observing.

[ub6ib969]

thanks mon2, I removed the R005 current sense resistor and measured 20M = 00.00 (RES 5m OHM 1W (1508) 1% CYNTEC/RL3720TT-R005-FNH0). I also went ahead and measured in diode mode 000.0V, if the R005 was shorted wouldn't it display .OL?

[mon2]

In diode mode, you will see 0V. Short your meter probes to confirm the same measurement. Keep this part off the board and power up. Do you now see the adapter voltage travel through both of the DCin mosfets? Actually, this will not work since the charger IC will detect that this resistor is missing and will power it down.

Will update this thread after a late lunch

[ub6ib969]

can I use a R010 sensor from a donor board ? thmx

[mon2]

The board design was created and calibrated to make use of the R005 = 5 milli-ohm resistor. You are considering to install a R010 = 10 milli-ohm resistor. While it does not sound like a large difference, the measurements will be off and can lead to other faults. Best if you stick with the original.

Can you share pics of the top and bottom side of the R005 resistor? Also the PCB pads where this part will be installed. Need to be sure the pads on the part and the PCB target sites are clean. They cannot be shorted.

[ub6ib969]

replaced R005 and same issue with PQ8901
P_CHG_ACMOS_S_20 = 0v
P_CHG_ACMOS_G_20 = 0v

when PQ8900 is removed
P_CHG_ACMOS_S_20 = 24.7v
P_CHG_ACMOS_G_20 = 20v

[mon2]

Clean up the current sense resistor target PCB pads with flux and desolder braid. You should have only 2 bars with pre-tinned solder to match the current sense resistor. Like an 'oreo sandwich'. The end edges cannot be shorting like the earlier picture. If they do, the current sense resistor is bridged and the charger IC is unable to gauge the current draw of the power rail.

[ub6ib969]

copy that. no bueno.

removed all caps and mosfets one by one on the AC_BAT_SYS line and shorts still exists

[mon2]

What is the exact resistance to ground of AC_BAT_SYS ?

While still in resistance mode, apply one meter probe onto AC_BAT_SYS. The other meter probe on any if the inductor. Checking for a low resistance path between the 2 test points. If found, then there is a high side mosfet leakage. Start with the CPU area. Post your findings.