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Old 05-03-2021, 12:50 PM   #1
diamon
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Default Laptop Asus ROG GX531GM dead

On my work (hobby) bench, I have a Asus ROG Zephyrus S GX531GM (gaming laptop), it's completely dead.
Removed the motherboard and I did find only the 19V rails on several points on the motherboard.
There is no voltage on the power button and the 25L12873F (bios chip) has also no voltage (pin 4 + 8).
The bios battery had no voltage any more, I have replaced this battery but no difference. A hard reset after removing the bios battery and external power (pressing the power button for 40 seconds also no difference).

Information from the motherboard is GX531GM Main Board Rev. 1.3

Searched for shorts on mosfets, did not find any. But all the caps i have measured (also the black ones) are shorted (see image which part of the board).


This is a full size picture of the board:


This is the part with the shorts:


Some one who has an idea. Did not find any schematics, so no clue where the voltages are generated (5v, 3.3v, 1.8v, etc..).

Last edited by diamon; 05-03-2021 at 12:55 PM..
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Old 05-03-2021, 01:12 PM   #2
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Default Re: Laptop Asus ROG GX531GM dead

hi. not aware of schematics for Asus anything. They appear to be locking away their secrets @ Fort Knox.

With a meter on resistance mode, check the resistance of each coil to ground.

Do you see any super low readings ?

Based on your post, one or more caps are shorted which is likely leading to a high current event and shutting down the local regulator.

You can trace the DCIN and see if there is a local SMD fuse (often white in color).

Can you zoom in where you apply the external adapter and share quality pictures?
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Old 05-03-2021, 02:04 PM   #3
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Default Re: Laptop Asus ROG GX531GM dead

https://badcaps.net/forum/showpost.p...02&postcount=2

Quote:
2.2. Don't suspect that something is shorted with no reason
Shorted components are not the only failure mode of a laptop. Additionally, some places will measure low resistance to ground under normal operation. In general, high power low voltage (<2V) power rails will measure less than a few hundred ohms to ground. CPU VCore will measure a few ohms only. GPU VCore with newer NVidia GPU can even measure less than 1 ohm. It's normal. If you suspect a short to ground, always report your exact resistance to ground measurements.
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Old 05-04-2021, 04:26 AM   #4
diamon
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Default Re: Laptop Asus ROG GX531GM dead

I have done the measuerments of these coils:
https://freeimage.host/i/BolafV
Coils from left to right
1,2,3,4,5,6: 00.8 ohm (setting on 200ohm)
7,8,9,10: 00,5 ohm (setting on 200ohm)
11: 7,4 ohm (setting on 200ohm)

There are also mosfets on the back of the board. I measure shorts on all of them, between the Drain and Source.
https://freeimage.host/i/BolGOg

Modelnumber of those mosfet 4C06B > https://datasheetspdf.com/pdf-file/7...r/NTMFS4C06N/1)
The vias from the 4C06B mosfets, are connected on the other side of the board to the coils (underneath the coils, I think top pad of the coils).

The mosfets on top of the board, are the 4C09B, they don't have a short between the Drain and Source (or gate) > https://datasheetspdf.com/pdf-file/8...r/NTMFS4C09N/1

Regarding a fuse on the board > DCIN, did not find any abvious fuses (non of the parts have any markings on the board, like F1).

This is the part where the DCIN connector is.
https://freeimage.host/i/BolWzJ (underside of the board)
https://freeimage.host/i/BolXWv (underside of the board > topside is the current resistor).
https://freeimage.host/i/BolhsR (topside of the board)
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Old 05-04-2021, 05:07 AM   #5
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Default Re: Laptop Asus ROG GX531GM dead

Quote:
Originally Posted by diamon View Post
I have done the measuerments of these coils:
https://freeimage.host/i/BolafV
Coils from left to right
1,2,3,4,5,6: 00.8 ohm (setting on 200ohm)
These seems fine because they are gpu coils and that low ohm reading is ok.

Quote:
Originally Posted by diamon View Post
7,8,9,10: 00,5 ohm (setting on 200ohm)
11: 7,4 ohm (setting on 200ohm)
These are not good. 7,8,9,10 are cpu coils and should be somewhere around 2 ohms at least.
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Old 05-04-2021, 07:01 AM   #6
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Default Re: Laptop Asus ROG GX531GM dead

Quote:
These are not good. 7,8,9,10 are cpu coils and should be somewhere around 2 ohms at least.
Based on the advice from @myth77, check the coils 7,8,9,10 and locate which caps are mating with each coil. Guessing the 2-4 large black polarized tantalum caps are linked to at least one of these coils (marked with 470 and 220).

Then with a hot air tool, consider to desolder one side of the cap so you can lift the cap to remove from this leg of the circuit. Then check the coil to ground resistance again. Does this remove the ultra low resistance value of 0,5 ohms?

There will be a lot of ground plane in these regions of the PCB so proceed with caution and patience. Flux on the cap solder tabs will be help. You can also apply leaded solder (which is low temp as compared to ROHS) onto the same solder joints to assist.

With this method, you can locate a possible bad cap. There is also a possibility of the CPU being bad but no direct experience with that topic...yet.
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Old 05-04-2021, 07:24 AM   #7
myth77
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Default Re: Laptop Asus ROG GX531GM dead

My advice would be to remove those 7,8,9,10 coils with heatgun and then check what side is shorted to gnd...pray that it is the other side(opposite to cpu) because if it is CPU side shorted chances are 99% that cpu is dead. That 1% is maybe, but just maybe that some cpu cap dead... but that is very rare.
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Old 05-04-2021, 09:12 AM   #8
diamon
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Default Re: Laptop Asus ROG GX531GM dead

I have lifted all the coils and those 4 caps, the side that's shorted to ground is above the CPU (not above those coils).
All those small caps are also measuring a short, also those black "New e8N" (caps?).

On the backside of the board, the short between the Drain and Source is gone now.

https://freeimage.host/i/BojVaf
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