Странное поведение Acer Nitro 5 AN517-41-R8NP, AMD, MB: GH51Z LA-K851P Rev:1B

The last time I repaired electronics was over 30 years ago – my first degree was as a specialized electronics service engineer.

Now, circumstances have prompted me to take up electronics repair again – and I've realized how much I've been missing. For several months, I've been trying to understand current trends in order to solve a problem with my daughter's laptop. Now I can draw some conclusions, share them with you, and ask for your help.

My daughter's laptop, an Acer Nitro 5 AN517-41-R8NP, stopped working and showed no signs of life. My daughter took it to two local computer repair shops, and both said the motherboard needed to be replaced. This made no sense since the motherboard was very expensive, so she gave me the laptop to experiment with. At the time, I had nothing but a Voltcraft VC-100 multimeter (as old as I am) and a regular household soldering iron.

To make this rather boring story short, I'll start with one recent fact: somehow, I found one faulty MOSFET, replaced it, and the laptop miraculously came back to life and worked perfectly for over three months.

Currently, I already have some equipment: schematic and boardview, but not for the GH51Z LA-K851P Rev: 1B, because I couldn't find Rev: 1B, but I did find one for the Compal GH51Z_GH71 LA-K851P Rev: 1A.

I now also have a heat gun, a decent soldering iron, an inexpensive but fully functional multimeter with a thermal camera, and an inexpensive x8 magnifying staff, etc.

Now we have two more problems with this laptop:

1. The laptop stopped charging the battery, even though the charging indicator is red. I checked the battery separately – it's perfectly fine.

2. The laptop turns on and works fine, but as soon as I increase the load using the graphics card (like games), the laptop runs for a bit and then shuts down.

3. I ran stress tests using Aida64: the CPU-only stress test runs normally, with stable temperatures. The CPU + GPU stress test runs for 3-4 minutes and then shuts down.

Observations and actions with our Acer GH51Z LA-K851P Rev: 1B:

Initially, when the laptop first failed, I replaced one MOSFET PQZ2 - E6930 – after that, the laptop worked fine for several months, the battery charged, and I could work and play games normally. Now (the battery isn't charging, the laptop shuts down under load):

1. The BQ chip was replaced, according to the schematic: PUB1 - BQ24781

2. The regulator was replaced, according to the schematic: PU301 - SY8288BRAC (BABXXXX)

Observations (the motherboard is out):

1. When power is supplied to the motherboard, with the battery disconnected, it draws a small amount of current – I can't say exactly how much, since I don't have an accurate meter, but approximately 20-30 milliamps. The PUZ1-RT3663BRGQW chip heats up to 40 degrees Celsius, and the PRZ11 2.2 Ohm resistor heats up to 35 degrees Celsius.

2. When powering up the motherboard with the battery connected (the battery is not charging, but the charging indicator is on), the PUZ1-RT3663BRGQW chip heats up to 40 degrees Celsius, the PRZ11 - 2.2 Ohm resistor heats up to 35 degrees Celsius, and the PU301 - SY8288BRAC regulator heats up to 30 degrees Celsius.

3. When connecting only the battery to the motherboard, the board is cool, nothing heats up.

4. If to connect the battery to the motherboard and apply external power for a second, you can observe continued heating up to 40 degrees Celsius for the PUZ1-RT3663BRGQW chip and up to 35 degrees for the PRZ11 - 2.2 Ohm resistor.

5. When the original PUB1 - BQ24781 was removed from the board, no heating was observed when external power was applied.

6. When the original PU301 - SY8288BRAC was removed from the board, no heating was observed when external power was applied.

Does anyone have any ideas: why does the laptop shut down under load, why doesn't the battery charge but the charging indicator lights up, why does the laptop completely discharge the battery when turned off, and why does current consumption and chips heating occur when the laptop is turned off?

1. What is the power adapter rating? If the power adapter is under rated, then the CPU will be throttled on the speed and battery charging will halt.

2. Check the voltage to ground of the ACDET on the charger IC. There must be a valid voltage here to denote that the power adapter is mated to the board. Often the DCin power jack is broken and allows for the mosfet @ PQB13 to enable. This then pulls down the **ACDET **voltage to ground so the board believes there is no adapter connected.

Hi, участник, thanks for response.

Original Acer power adapter 19.5V-9.23A 180W is in use and it has been tested, as well as batt - with another different but similar Acer nitro 5. No cpu throtling has been observed on Aida64 stress test, as it was mentioned.

Thank you for advise, I'll check that mentioned voltage accordingly and will reply here tomorrow.

Suggest to test PQB1 & PQB2 mosfets using resistance mode. Remove all power.

Check:

**source / drain

source / gate

gate / drain**

Each should be hundreds of k ohms or higher else is a suspect. The charge voltage should be higher than the battery pack voltage.

Test the full path resistance between pins 19 & 20 and compare to the schematic value. If the board powers up with the adapter only then ACDET is most likely ok but worth a quick test. Also test PDB1 to confirm it is not leaking. A common point of failure. Also test series resistor @ PRB12.

Greetings, friends.

I solved the problem described above, and the solution turned out to be very simple – replacing the PQB11 (EMP21N03HC) MOSFET.

The EMP21N03HC MOSFET wasn't working, but it wasn't shorted. I replaced it with a PH5030AL MOSFET.

The laptop is now fully functional and passes all stress tests.

Thank you all for your support.

I hope anyone else encountering the problem described above will be able to use this solution.

Good luck everyone!