Asus ROG G751JY No Power (Short)

[TheWizard]

Hello everyone. I have an Asus G751JY motherboard that will not power on.
- Charger has been tested. Reading 19v when connected to wall.
- DC/IN has been confirmed to be good. Reading 19v
- Everything circled in first pic is showing 19v
- I tested random components and found 5v and 3.3v producing.
- In diode mode all these mosfets (pic2) are showing like a 0.4 voltage drop..But when i read the inductors they are triggering a beep from diode mode and showing short.
- I took readings from.the inductors in resistance mode and they are all 6.5 and the 6.5 follows direct to the caps above the inductors.

Does anyone know the stand by voltage locations for this board? I have the board view. But would love it if anyone had a schematic to share. Seems like they are gold now lol

[TheWizard]

Disregard: This one is fixed. Shorted N- Channel Mosfet PQ8511 on G_PWR_SRC_NVVDD. Happy Holidays Everyone!

[TheWizard]

Friends this one has resurfaced. Laptop powers on and everything works except the battery does not charge. Laptop recognizes when the AC Adapter is connected and disconnected. But when the adapter is connected. Status shows connected but battery does not charge. I have replaced the 3 mosfets pictured since start of this repair. When only the battery is connected the connector reads 14.34v on the first 3 pins, then 3.25v on pins 4&5. Followed by the 3 ground pins. This seems normal to me. I have confirmed all rails are present. The battery is brand new. Issue persists with original battery as well. I have confirmed there are no shorts on the AC_BATT_SYS. I also ordered a new DC/IN port that I will be replacing next week after arrival. In the meantime i was going to check the UP1661PQAG charging chip's readings. I have yet to find a datasheet for this to reference pin out. Does anyone have any other ideas? Am I missing something? I have read numerous posts in forums about battery charging issues with Asus laptops.Thanks for reading.

[TheWizard]

Update: New DC/IN port has been installed and charging issue remains. Anyone have simular issues with an Asus board?

[mon2]

Based on the following diagrams, I do not think that up1661 is the charger IC:

https://kythuatphancung.vn/forum/ind...-giá-70000đ/

[mon2]

Hunt around the battery connector for a square ic with topside ‘BQ' markings. Post a clear pic and the full markings if found. This will be your charger ic.

[mon2]

From another thread on this forum, the charger ic is:

bq24375

locate it and post a pic of this part.

[TheWizard]

mon2,
Thank you for reaching out. Much appreciated. This chip is directly beside the battery connector but it reads EL U580. The boardview says the part is PU8502. I am not finding a BQ chip. Here are some pics..

[mon2]

Charger IC is @ PU8800.

[TheWizard]

Yep you are correct. Just looked PU8800 up on boardview. Wow on the opposite side of board. Here are some pics... Looking up pinout.

[mon2]

With a steady hand, proceed to measure the voltage to ground of the following pins of interest:

(attach the power adapter)

ACOK (pin # 5)
ACDRV (pin # 4)
REGN (pin #16)

Post each measurement.

[TheWizard]

ACOK = 3.06v
ACDRV = 19v
REGN = 6v

[TheWizard]

mon2,
Everything seems normal for the readings right? I have readings on all pins except for ground (pin 14) as normal in diode mode. Need me to post them.as well?

[mon2]

Yes, these measurements are ok. When the adapter AND battery are connected, does the desktop in Windows show the presence of the battery? Is the battery 100% compatible with this unit? The communication is over SMBUS which you have confirmed are not stuck SDA / SCL lines.

When you have the battery connected, what is the voltage on the +V (3 pins) on the battery? At this stage, the charger IC should attempt to charge the battery. You can review the voltage to ground of SRN and SRP pins = current sense loop for the battery leg.

Next, remove all power -> meter in resistance mode -> measure the resistance between SRN and SRP pins on the charger IC itself. You are confirming that the current loop path is not of a high resistance between these 2 test points. Post all measurements.

[TheWizard]

Okay good. Yes, when the laptop is in Windows the presence of the battery is there. Battery light is indicating charging but never charges. Battery is currently at 11% but it did this when it was 56% out of the box. I deleted and reinstalled the battery in Windows. Indicator shows charging and you see charge progress. But then about a minute in it stops. Yes, the battery is fully compatible with laptop. Bought from ifixit a week ago. The voltage is 14.34v on the +v pins when just the battery is connected. Orange and Blue are 3.25v. I will act on your last directions and post readings here shortly. Thanks

[TheWizard]

Voltage

SRN = 0.815v
SRP = 0.815v

Resistance

SRN = 1.9 Mohms
SRP = 1.5 Mohms

[mon2]

SRN = 1.9 Mohms
SRP = 1.5 Mohms

Remove all power. Meter in lowest resistance scale if manual version.

One meter probet on SRN pin on the charger IC. Other meter probe on the SRP pin on the charger IC. We are testing for the full path resistance between these 2 pins to compare against the reference design / schematics.

[TheWizard]

Sorry misread that. Thought you wanted resistance to ground.

17.9 ohms from SRN to SRP pin of Charger chip.

[mon2]

This resistance check looks ok. Next, locate the battery mosfet on the board. We need to check each and every mosfet linked to the charger IC as one of them may be leaky.

This battery mosfet will be close to the battery connector and is responsible to pass the battery voltage onto the main power rail to power the logic board. This mosfet may be leaky. We can check it by reviewing the mosfet resistance.

Remove all power -> meter in resistance mode.

Measure the resistance across:

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

You can locate this battery mosfet by performing a resistance check. Use the lowest resistance scale OR use diode mode. Short your probe and meter should tone beep (in diode mode). One meter probe onto the +V (3 pins) of the battery connector. DO not have the battery connected. Other meter probe on the source pins (1-2-3) of the mosfet under review. If you hear a tone beep, you may have located the battery mosfet. Next, check the RESISTANCE from the GATE pin #4 of this same mosfet under question to the BATDRV pin on the charger IC. If this resistance is ~4k then 100% you have located the battery mosfet. Otherwise, repeat this procedure to the next mosfet nearby.

[TheWizard]

mon2,
These are the mosfets to the left of where the battery connector is located on the board. All are reading between 15 and 19 ohms from source to drain and source to gate. Diode reading from +v pin of battery connector to the source of these pictured mosfets creates no beep from meter.