Asus ROG Strix G (gl531gu-wb53) No power

[FiguringITout]

Hello,

I've been trying to figure this out for a while and am stumped. Help would be appreciated.

I have this ROG laptop that is not powering on and has no signs of life. I took it apart and started measuring finding no obvious shorts, all coils looked fine and input mosfets are reading good resistance.

I followed schematics I had found on the forum (linked below) and started following the power to the charge controller (PU8900, BQ24780SRUYT).
VCC - 19.65v
REGN - 6v
ACDET - 1.6v (this is what I believe is the problem)
ACOK - 0v


Following the schematics, I followed ACDET back to PR8904, which has 19.92v before it, but it drops to 1.6v after. I removed the IC PU8900, to see if it was pulling the value down but it stayed the same. Both resistors and the capacitor on the P_CHG_ACDET_10 line measured correctly out of circuit.

What's next on my shopping list? I feel like I'm 2 steps away but my lack of experience and knowledge is preventing me from finding that Ah-Ha moment. Should the IC be replaced? Are the input mosfets bad? Please help, I'm still trying to figure this all out.


Schematics and BV:
https://www.badcaps.net/forum/troubl...-1-6-schematic

[FiguringITout]

Sephir0th , Forums messed up but I saw your comment. I had the tab open from when I originally commented and rewrote it for you and anyone else needing assistance:


Thank you. Originally, I tested in continuity mode and it didn't beep. I just rechecked it and it was reading all over the place. I found that my multimeter is reading resistances incorrectly. In example, ground pad to ground pad, it reads 15ohms fluctuating, redoing the connections and turning the device off and on again showed 2ohms then climbing to 50ohms then back again. I didn't see anything obviously wrong after taking it apart so I went out and bought another multimeter, and found the following:


the AC_Short_Protection is low, around 10ohm. I injected voltage (.8v, 2a) and after spotting heat and cleaning the putty off, found this beautiful sight on the VRAM mosfet (PQH9404, FDPC5030SG).

I removed the fan connector first, as I didn't want to burn it. Then removed the mosfet. Not the worst damage, only hit the first layer from what I could find after cleanup. I decided to cut the pad further back to get it away from the problem area and then applied the green UV junk. Luckily enough, I actually had a similar n-channel mosfet FDPC5018SG that I had ordered for a different Asus device I worked on half a year ago. Installing that and checking resistances showed no more short and this was confirmed as I plugged the battery in and it started charging it again. I started putting it all back together and the fan connector decided it didn't want to live anymore (R.I.P.), but I wanted to test so I continued without the fan connected.


Good news: It now boots! Yay!



Bad news: All of the backlights are blinking constantly. Aww.

Turning off the backlights works, as do all other functions in my very limited bios keyboard test. I figured this may be the system yelling at me for not having the gpu fan connected, so I VERY GENTILY removed a spare with low melt and after cleaning it off soldered it to the proper board. Unfortunately it still blinks. I updated the BIOS to see if that helps, also reached out to the previous owner to see if it was a setting that may have been applied but no dice.


The laptop is working again, though the mosfet I replaced it with isn't a perfect match so I ordered the correct one and will use that before stress testing it. If anyone knows why the laptop is blinking please let me know. It appears to stay solid during the first second of booting, but starts flashing after it begins to load.

[Sephir0th]

a) in cases the highside-Mosfet between Main Power Rail and FBVDDQ is shorted, the GPU (memory controller) has most likely died (laptop is working on iGPU instead).

b) you are not allowed to play with the Buck Converter in this area. The Mosfet has to be a exact match or at least a proven replacement, otherwise you could damage the device more than already is. You can replace a FDPC5018SG with a FDPC5030SG but but not the other way around. Gate charge (Qg) of the FDPC5018SG is too high. Next time just wait for the Dual-Mosfet arriving.

The "blinking" wasn't described really good but i assume you mean the keyboard backlight. Possible reason could be the the acknowledge of the dead GPU but it could be also something completely different. Need to be inspected again when the time has come.

[FiguringITout]

You are correct, the GPU is reporting code 43, so it's dead. Thank you for your clarification for the mosfet. Since the GPU isn't working, would replacing the mosfet even matter or would the higher gate amperage affect the laptop in other ways? Going forward, I will make sure to replace chips with their proper replacements (or upgrades) instead of ones that are "good enough".

The blinking was fixed after a full reset and reinstalling armory crate. It was set to strobing, and kept its settings even after I reset the device through windows.

I'm currently typing this on the laptop, which should make me a good shop laptop considering the broken GPU. It has a nice keyboard and beautiful RGB so I'll give it that.


Thank you for your help.