Acer Aspire 5741G (MB: LA-5891P) Missing "DGPU_PWR_EN" signal

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Brand: Acer
Model: Aspire 5741G-434G50Mn
Motherboard: Compal LA-5891P, Rev.: 1.0 (With dedicated GPU)
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Hello!

I'm working on the mentioned laptop, which the following symptom: After pressing on the power button LEDs turns on, but it is nothing on the screen (no picture, no backlight).
GPU is cold, CPU is only little warm. No graphics power supply voltages.

I found out that it is missing "DGPU_PWR_EN" signal from PCH. On mentioned line is 0V (if I'm not mistaken it should be 3.3V).
Resistance to ground on line "DGPU_PWR_EN" is 99kΩ.

What I've done up to now:
a) Resetted CMOS -> no changes.
b) Reflashed BIOS (Main + EC) -> no changes.
c) Diagnostically heated PCH (with hot air gun) -> no changes.

I think it could be bad PCH, but I'm not sure.
Any idea?

PCH is ignoring heating, try reflow, reballing, if not work - replace.

PCH replaced with new one.

Now the symptoms are different:
-When I connect the charger (without battery) charging LED "LED2" turns ON, and after 20 seconds it starts flashing.
-When I press on the power button power LED "LED3" turns on, fan spins, but after 4 seconds laptop shuts down, and restarts itself in loop.
-If I hold down the power button laptop turns OFF.
-If both, the battery and the charger are connected charging LED "LED2" turns ON, and it doesn't starts flashing.
-If only the battery is connected laptop also reacts to the power button, but it also shuts down and restarts in loop.

When the laptop is turned ON all voltages are present. PCH, CPU and GPU are little warm.
RTC crystal "X2" oscillates all the time.

I don't know, maybe it is unsucceed reball of PCH.
Any idea?

PCH needs a higher temperature from below, for example 180 degrees Celsius, these motherboards bend if heavily heated from above.
Try reball on Pb.

Type5 napisał(a):PCH needs a higher temperature from below, for example 180 degrees Celsius, these motherboards bend if heavily heated from above.
Try reball on Pb.

You didn't understand me.
I ordered brand new PCH. It comes with lead free solder balls, so I reballed it with leaded solder balls, and attached it to the board.

You tried raball on original PCH?

Type5 napisał(a):You tried raball on original PCH?

No, I don't.

Hello!

After a few months, I found some time to continue with repairing this laptop.

I reballed the old original PCH chip and attached it to the board -> The symptoms was exactly the same like with new PCH described in post #3.

I decided to replace the KBC chip, which solved many issues. Now the battery charges OK, the laptop boot, everything is working OK, except that the GPU is not detected.
I replaced the PCH chip again with the new one -> nothing changes (GPU is still not detected).

After replacing PCH, the laptop shuts down exactly after 5 minutes, the fan was running at a high speed -> Cleaning the BIOS ME region solved this issues.


In Short:
Now everything works OK, except that the GPU is not detected.
Device Manager, CPU-Z software:


- The GPU power supply is ok, the GPU is normally hot.
- Brand new KBC and PCH chips -> no changes.
- Cleaned BIOS ME-region -> no changes.
- BIOS reflashed with this one -> no changes.
- Diagnostically heated GPU (with hot air gun) -> no changes.

GPU is ATI 216-0774007
Should I do something else before reballing/replacing the GPU?
I do not see the reason that it would be bad KBC and GPU chips at the same time.

GPU reballed, now everything works as it should.

Thank you @Type5 for contributing to resolve this issue.