Acer Nitro 5 AN517-52-56A5 - won't charge, shorts the AC adapter

[gleniu]

Hello,

I have a problem with Acer Nitro 5 AN517-52-56A5 (motherboard: GH51M LA-K862P Rev: 1A). I was playing TLoU2, which is a rather demanding game, for a few hours, unless the notebook turned off (my guess is that the battery drained to 0%). Now, when I connect the AC adapter, the LEDs are not coming on and the laptop doesn't charge.

It also shorts the AC adapter - I've checked two of them from different manufacturers. Though the AC adapter gives 19,5V as expected, the voltage drops to 0V when I connect it and disconnect from laptop - it comes back to 19,5V when I reset it by unplugging it from power outlet.

I checked the power socket - multimeter shows no shortage between + and -.

It has to be something on the motherboard that cause the shortage. The thing is that although I can use multimeter, soldering iron and hot air without issues, I have no idea how to look for the defective components.

Could anyone please guide me through the whole process of examining the board, step by step, to find the defect? I would gladly donate anyone who is eager to spend some time helping me on this one.

Thank you!

[mon2]

See attached. Remove all power. Meter in resistance mode.

Locate the parts behind the dcin adapter connector. There are a few ferrite beads (coils) behind this connector.

Place one meter probe (either color) onto the tips of the PL101 ferrite bead; other meter probe to ground (metal shield is ok). What is the resistance in ohms showing on your meter?

We are checking if there is a short on the main DCin power path by testing the resistance. A low resistance is often bad.

[gleniu]

Thank you for responding so fast!

So, I've put my multimeter in 20k Ohms mode and it showed following values - please see the image with arrows attached:

1. Black probe on GND, red on arrows:
- green arrows: 9.50
- red arrow: 0.00
2. Red probe on GND, black on arrows:
- green arrows: 17.92
- red arrow: 0.00

[gleniu]

I've been googling and reading about it and I think that the PQB11 MOSFET might be dead.

I measured it in diode test mode and I get the following results:
1. Red probe on source, black probe on drain: 0.000V
2. Black probe on source, red probe on drain: 0.000V
3. Red probe on gate, black probe on source: 0.621V
4. Black probe on gate, red probe on source: 0.494V
5. Red probe on gate, black probe on drain: 0.620V
6. Black probe on gate, red probe on drain: 0.492V

I'm attaching a photo with source, drain and gate marked according to my measurments - hope I haven't done a mistake here.

Do the results I got prove that the MOSFET is indeed dead? Now I'm planning to remove the MOSFET and measure it while desoldered, also measure pads on motherboard. But before I do so, I would love to get some feedback and make sure that I'm following the right path.

What I'm affraid of is that I've read on some other forum that if this MOSFET is dead like in my case, there is a huge possibility that CPU got 19V and is burned right now, meaning the notebook is basically dead. What do you think?

[mon2]

Yes, the mosfet looks to be shorted. Flux and remove and replace this part. Double-check the mosfet after it is removed and on your workbench.

Repeat the testing for the next DCin mosfet that is to the left of your picture. Confirm that this mosfet is ok or that it is also defective. The CPU risk with another mosfet that is the high side mosfet that mates with this main power rail. For now, do not be concerned about the CPU mosfet. The DCin mosfets are a common point of failure. Review the sticky article on charger circuits above by piernov for full details of your case.

This defective mosfet can be replaced by many others from donor boards. Post details of the mosfet you pan to use as a replacement before soldering it into place. Use flux + hot air with low air pressure to prevent the loss of the tiny parts surrounding these mosfets.

[gleniu]

Thank you, I will do it today evening or tomorrow. The mosfet to the left of the faulty one (the left side on my picture) is good - it doesn't short.

As for donor board, I only have old Clevo P670HS-G somewhere in the basement. Not sure if I can find something matching there, so I was thinking about ordering MOSFET. If you have any recommendations on what should I order, I'd be very grateful for these.

[mon2]

The original is part # PK5NEA. Aliexpress should offer them if you are after the same.

The part can be replaced by many others.

The key specifications are:

(in order of importance)

1) be the same type. This is a N-channel mosfet.

2) same size. This is a 5*6mm package.

3) Support 30V source/drain. Most do but check. If on a laptop, very likely will be similar in specs.

4) Ideally the same support for peak current or higher.

Once you find the donor board, post the topside markings to review if it is a suitable fit.

Alternatively, do you have access to electronic parts shops in your region? Another dead laptop board may offer a suitable replacement mosfet.

Digikey / Mouser / Arrow / RS electronics will offer suitable replacement mosfets.

[gleniu]

Unfortunately I live in a small town, but I can order MDU1511 online for a good price. AI says it is 100% compatible, but I'd like to confirm with experts before ordering.

[mon2]

Yes, it is a valid replacement. Better than the original.

[gleniu]

About that second MOSFET (B09N03) - I measured it once again (on the board) and it shows following values in diode test mode:

1. Red probe on source, black probe on drain: 0.516V
2. Black probe on source, red probe on drain: 1.402V
3. Red probe on gate, black probe on source: 0.611V
4. Black probe on gate, red probe on source: 0.487V
5. Red probe on gate, black probe on drain: 0.928V
6. Black probe on gate, red probe on drain: 1.388V

Does the above mean that this second MOSFET is defective as well? Or might it mean that something else is shorted?

Please note that I measured this MOSFET while the first one was still in place (not removed).

[mon2]

Suggest to use resistance mode on your meter and then test again. Post each measurement. On a good mosfet, the measurements should be hundreds of k ohms or higher.

[gleniu]

Thanks, will do it shortly. For now I managed to desolder it (that damn GND pad added me some gray hairs ) and it still shorts and there is no short on pads on motherboard, so I believe it really was faulty.

Unfortunately I accidentaly desoldered the PRB47 and I need to put it back in place. Can you please tell me if it's polarised and has to be put in the correct way or it doesn't matter?

Sorry for asking noob questions, but I'm not even really sure what is this. For now I believe that this is a resistor and I can put it back in place any direction.

[mon2]

Do you mean PRB4? Unable to find a PRB47 in the schematic. No polarity to resistors.

PRB4 = 4R7 ohms 0603 SMD resistor. Order a few of these if placing an order. Otherwise, replace with any value of 10-100 ohms here.

[gleniu]

I mean this one, maybe I have a different schematics file?


It is really tiny, but I haven't lost it, so I will just try to put in in place.

I will come back with measurements shortly.

[mon2]

This part is a thermistor - acts like a temp sensor. No polarity but is required to be present else the logic board will have off measurements for the temps in this region of the board.

[gleniu]

Thanks, I managed to put it in place.

Is it a good idea to plug in my DC adapter with MOSFET removed just to check if it still shorts? Of course I won't be powering on the machine, anyway the motherboard is completely out of notebook's body now.

[mon2]

Test the resistance of the removed mosfet that is on your workbench.

source / drain
source / gate
gate / drain

Each measurement must be hundreds of k ohms or higher else it is defective.

Yes, you can test the board without this mosfet noting that the power path is incomplete so the adapter should not short unless there is a fault between the power adapter connector and this removed mosfet. Post your updates.

[gleniu]

The measurements of removed MOSFET in resistance mode:

1. Red probe on source, black probe on drain: 0.1Ω
2. Black probe on source, red probe on drain: 0.1Ω
3. Red probe on gate, black probe on source: 1.00kΩ
4. Black probe on gate, red probe on source: 1.10kΩ
5. Red probe on gate, black probe on drain: 1.00kΩ
6. Black probe on gate, red probe on drain: 1.10kΩ

[gleniu]

The measurements of the second MOSFET in resistance mode:

1. Red probe on source, black probe on drain: 64.8Ω
2. Black probe on source, red probe on drain: 106.4kΩ
3. Red probe on gate, black probe on source: OL
4. Black probe on gate, red probe on source: 53.2kΩ
5. Red probe on gate, black probe on drain: OL
6. Black probe on gate, red probe on drain: 105.2kΩ

I think that this one looks good and we're close to saying for 100% percent that the PQB11 is the culprit, aren't we?

[gleniu]

Yes, you can test the board without this mosfet noting that the power path is incomplete so the adapter should not short unless there is a fault between the power adapter connector and this removed mosfet. Post your updates.

Also, the power adapter doesn't short now, with the MOSFET removed.