Acer Predator GH51M LA-K862P

[aico60]

Hello Guys,

I recently bought a non-working Acer laptop, motherboard GH51M LA-K862P.
I bought it with the intention to fix it.

Started with measuring some points of the MB.

I am suspecting that either the power supply of the CPU is shorted or the CPU itself is.

I am measuring 0 Ohms on PLZ4,PLZ3, PLZ2, PLZ1, which are for VCC_CORE, as well as PLV2, PLV3, PLV4, PLV13 - NVVDD1 .

The board is turning on with no display.
The GPU coils are measuring about 0.7V but the CPU is measuring at 0.1V.

Also the DDR_DRAMRST#_R is 0.1V.

After taking a look at the MB while it's on with a thermal cam, I noticed that a cap PC1106 near PU1101 (+1.05VALWP) is getting hot.
When I measured the cap, I got the following readings:
pin 2 which is connected to the PU1101 pins 20, 19, 6 - 1.1V
pin 1 which I am not sure if it is connected anywhere - 6V.

I was not able to find how 6V is getting to the cap.
Screenshot 6V.png attached for clarification.
The resistor on the left side of the cap (PR1102) is missing, but I am measuring 6V on both of the solder points.

Any ideas on how to check if the CPU is bad and where the 6V on the cap are coming from?

Boardview and pdf schematics are attached.

Thank you!

[mon2]

Re: Acer Predator GH51M LA-K862P

Remove all power. Meter in lowest resistance scale.

Measure the resistance to ground of +1.05VALWP.

What is the reading?

[aico60]

Re: Acer Predator GH51M LA-K862P

It is measuring at 39.9 Ohms.

[mon2]

Re: Acer Predator GH51M LA-K862P

The resistance is ok.

The missing resistor at pr1102 is listed in the schematic as a 0 ohms component. Being this value, to save on the cost of the part and the stuffing fee for this part, the vendor may have opted to just apply a PCB jumper or trace for this site.

Check the resistance across the pads of pr1102. No power to the logic board when checking resistance or if in diode mode.

It should be ~0 ohms?

[Sephir0th]

Re: Acer Predator GH51M LA-K862P

In my opinion there is no point to continue as long as the CPU Core rail measures Short to GND. 2 Ohms might be okay. 0 Ohms is not.

Additionally, PC1106 measurements looking absolute normal to me

[mon2]

Re: Acer Predator GH51M LA-K862P

I think the op is measuring the resistance across the coil pins and not to ground. Please clarify.

[aico60]

Re: Acer Predator GH51M LA-K862P

Thank you, guys.

Will check resistance of both pins of PR1102 once I get home.

I am measuring the coil resistance from GND to one of the coil pins.

Since it looks like the CPU (I5-10300H) itself is short, I am thinking of finding a repair shop where they can replace it with the CPU from another board I have. It has I7-10750H.
I checked the CPUs in Intels website and they have the same BGA socket and can work on the same chipset (HM470). Both MBs have the same chipset.
Measuring the CPU coils on the other board I get about 4 Ohms, so the CPU should be ok.

Do you guys know if BIOS modificitaion will be needed for the CPU support or should it work out of the box after the replacement?

[aico60]

Re: Acer Predator GH51M LA-K862P

Checked across both pins of PR1102 - 0 Ohms.

What do you think about the CPU, would it work if the cpu is swapped with an i7 one?

[mon2]

Re: Acer Predator GH51M LA-K862P

From my limited knowledge of this area - many shops in Asia do this all the time. Check youtube videos, etc. but it is not an easy replacement.

#1 - you must have a quality BGA rework station to carefully remove the defective CPU
#2 - then the pads must be tinned with low temp (aka leaded) solder
#3 - then the BGA pads must be flattened down -> careful to not rip off a PCB trace - have a WLCSP packaged device where the trace lifted - it is thinner than my hair strand so will be fun to repair. Will use UV glue and UV light to return the single trace that now has an erection. Almost lost the trace but found it under our new 4k microscope.
#4 - flux the entire region again
#5 - back to using the BGA rework station to flow it back onto the board

Software mods is another possible requirement. It is all on our work to do list but no direct experience...yet.

Check our Master Liu's videos and possibly Rewatech on YT.

Found a few that are on topic:

https://www.youtube.com/watch?v=bAfNzP29d3o

https://www.youtube.com/watch?v=yqYgB6N2ijM

https://www.youtube.com/watch?v=c3Rin6O8Tns

[aico60]

Re: Acer Predator GH51M LA-K862P

Thank you, mon2!

The CPU was replaced today in a repair shop, now it is measuring at 2 Ohms.
However, the laptop is still failing to turn on.
I am not getting DRAM_RESET, it is measuring at only 0.2V.
Also pin 5 on bios chip is about 0.18V.
Once the power button is pressed, it jumps to 3V and drops immediately on 0.18V.

I could not find anything else.

[mon2]

Re: Acer Predator GH51M LA-K862P

Attach the power adapter.

Carefully measure the voltage to ground of the following points of interest on the charger IC (PUB1):

REGN
VCC
ACDRV
ACDET
ACN
ACP

Post each measurement.

[aico60]

Re: Acer Predator GH51M LA-K862P

Sorry, I might have mislead you.

The laptop is turning on, the fans are spinning but does not POST.

CPU, GPU, Chipset are all heating up.

Should I measure the charger IC anyways?

What is bothering me is that on PU1101, pin 1 is outputting 6V instead of 1V. Is this expected?

[Sephir0th]

Re: Acer Predator GH51M LA-K862P

CPU Core voltage is present now? VR_Ready and PLT_RST# asserted?

And regarding PU1101/PC1106, i can't tell you much about how Bootstrapping voltage is created, but you must _not_ confuse bootstrapping with VOUT.
AGAIN: everything is in expected ranges there.

[aico60]

Re: Acer Predator GH51M LA-K862P

CPU Core is present now - about 0.9V.

PLT_RST# is 3.3V

Couldn't find VR_Ready but found some similar ones, which is the one you asked about?
VR_ON - 3.3V
VR_HOT# - 1V
81215_VR_HOT - 1V
VR_PWRGD - 3.3V
VCCCORE_VR_PWRGD - 3.3V

[Sephir0th]

Re: Acer Predator GH51M LA-K862P

That's bad my friend. It's possibly the case, someone soldered a bad CPU to your board. However, you should rule out a corrupted BIOS in any case.

[aico60]

Re: Acer Predator GH51M LA-K862P

Why would the CPU be bad?
Which measuring shows that?

The CPU might indeed be bad as it was taken from another broken laptop but still...

[Sephir0th]

Re: Acer Predator GH51M LA-K862P

No measurement shows that and this isn't even the point. There are indicators. You know, the things where a good detective looks for when it seems impossible to get proofs. Like the missing DRAMRST#, the unknown condition of the CPU, mixed up with the potential risk of it wasn't soldered properly in addition, and so on... so the chance of a Healthy CPU decreases and decreases...

If you just believe in measurements, you'll always get stuck when you have to challenge a "hard fault". Especially Static resistance measurements can easily trick you then.

Also the big BGAs can fail in various ways, not only.power-related. There exists ways they fail, even myself might not think of. Not even mentioning to catch these faults with a tool.

[aico60]

Re: Acer Predator GH51M LA-K862P

Hello,

The VCore measures at 2Ohms.
Also when I inject 0.8V at the CPU (I know this is a bad thing to do but wanted to test it out) it does not take more than 1.2A.

Another thing is that I do not have PCH_SPI_CLK on pin 6 of the SPI. It stays at 0V.
Also, the 5th pin of the SPI is 0.1V. It jumps to 3V when I press the power button and immediately drops to 0.1V.

Is a bad PCH a possibility in this case?