Acer Nitro 5 AN515-45 not charging

[CPUFiddler]

Hi there. I am trying to repair an Acer Nitro 5 AN515-45 and it's giving me some trouble. I have access to SMD rework station, variable power supply, digital oscilloscope, thermal camera, multimeter, stereo microscope.
This laptop will boot and run from the power brick and/or the internal battery, but it will not charge the battery. NirSoft BattInfo tells me the charge/discharge currents, so I'm confident in saying that it's not charging. In addition, there's no increase in voltage at the battery connector when the laptop thinks it's charging, not even a few millivolts.
I've downloaded the schematics and boardview files from this website and kinda-sorta I am able to follow the circuit logic.
Diagnosis done so far: Original battery replaced with new, genuine part. Removed board and inspected it for water damage, none found. Blown capacitor PCZ18 found and removed along with the vaporised copper from around it.
The schematic "Compal GH53Z MB LA-L031P GH53Z MB PDF.rar" that I downloaded from this website, on page 85 shows the battery charging circuits. It appears quite similar to the diagram you have in your sticky "Laptop battery charging circuit", post #2 and if I'm right it would appear to be an HPB buck circuit, and can draw power from the battery even when on mains power, if the demand is high enough. My theory is that the blown cap PCZ18, on the +19VB_CPU line, which is connected to the +19VB line via a choke, as it failed has demanded so much power that the HPB circuit has allowed a massive current flow which blew the short clear, but also killed the MOSFET responsible for charging the battery. I've ordered a pair of AON7506s and intend to replace PQB1 and PQB2 as I believe one or the other is dead. I originally was drawn to PQB13 as the faulty component, but I don't really understand the circuit. Please, would somebody look at the diagram for me and provide some guidance? I would be very grateful. I will respond as fast as I can.

Many thanks - Katie.

[mon2]

Remove all power. Meter in resistance mode.

Measure the resistance between pins 19 & 20 on the charger IC @ PUB1.

[CPUFiddler]

Will do so in around an hour's time. What sort of value should I expect?

[mon2]

~20 ohm = 10 ohms + 10 ohms as shown in the schematics.

[CPUFiddler]

Resistance from pin 19 to pin 20 on PUB1 is 20.5 ohms, allowing for probe lead resistance. PLB1 and PLB2 are intact, as is PRB19. The MOSFETs PQB1, PQB2 and PQB13 all appear undamaged with no discoloration when viewed under the microscope.

[mon2]

This leg of the circuit is ok.

Remove all power. No battery. Meter in DIODE mode. Touch your meter probes together and you will hear a tone beep.

Locate the dual diode that powers the charger IC @ PDB1.

Place the red meter probe on pin # 3; black meter probe on pin # 1 - meter should conduct. What is the voltage?

Reverse the meter probes and meter should block. Confirm this.

Repeat with pins # 2 & # 1 - same expected results.

We are checking if this dual diode is leaking. I recall a case here in the forum where there was the phantom charging in the absence of the power adapter and it was due to this part being defective.

[CPUFiddler]

red probe on pin 3, black probe on pin 1 = meter shows 217
black probe on pin 3, red probe on pin 1 = meter shows open circuit, 1

red probe on pin 2, black probe on pin 1 = meter shows 217 or 218
black probe on pin 2, red probe on pin 1 = meter shows open circuit, 1

red probe on pin 3, black probe on pin 2 = meter shows 360
black probe on pin 3, red probe on pin 2 = meter shows open circuit, 1

[CPUFiddler]

Unfortunately I won't have access to this board again until Saturday 10am UK time. Thank you for the advice so far.

[mon2]

The dual diode is ok. Not leaking.

[CPUFiddler]

I have access to the board today, and a multimeter. The two MOSFETs arrive tomorrow.

[mon2]

The mosfets may be ok but you can test using resistance mode.

Remove all power. Meter in resistance mode.

Meaure the following permutations:

source (1-2-3) & drain (5-6-7-8) ; pick one pin in each group - color of the leads is not important in resistance mode
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. Each measurement should be hundreds of k ohms or higher if the mosfet is ok. Otherwise it is a suspect.

Repeat the above for each mosfet linked to the charger IC. Hunting for leaky mosfets.

[CPUFiddler]

Some of these readings did vary and I'm not sure if that's simply because the currents are so small. I'm using a Fluke autoranging multimeter from the 80s.

PQB1
Source-Drain (Pins 1 & 8) = 2MΩ
Source-Gate (Pins 1 & 4) = 210KΩ
Gate-Drain: (Pins 4 & 8) = 1MΩ

PQB2
Source-Drain (Pins 1 & 8) = 2.2MΩ
Source-Gate (Pins 1 & 4) = 190KΩ
Gate-Drain: (Pins 4 & 8) = 1.7MΩ

PQB13
Source-Drain (Pins 1 & 8) = 1.2MΩ
Source-Gate (Pins 1 & 4) = 2.5Ω
Gate-Drain: (Pins 4 & 8) = 1MΩ

I doubt that these MOSFETs are particularly light-sensitive but I should mention I had an LED floodlight on a camera mount pointing at the board, to help my 58yr-old eyes focus.

I have ordered three AON7380s from eBay. They could take up to a month to arrive even though they're in the same country I am :-(

Mon2, thank you for your guidance.

[mon2]

For sure PQB13 is defective. The other 2 are suspects due to the ~200k ohms resistance which is considered to be low for a mosfet. It may be faster to source from Aliexpress with the faster shipping methods. We often find those methods to arrive in Canada in about 2 weeks from China with tracking. Suggest to order spares of each PQB1 / PQB2 / PQB13. There are some valid replacements on Digikey but a quick search shows them to be ~7 or so days for arrival so may as well remain with Aliexpress, etc.

The mosfets are not light sensitive but open smartcards are - using a high intensity strobe light is a known hack to compromise these security cards.

[CPUFiddler]

I have ordered replacements for PQB1, PQB2 and PQB13. If there are any other components you would recommend I replace, by all means, let's reduce the shipping time by immediately grabbing them. Sorry if language is unfriendly.

[CPUFiddler]

I am in the UK so China shipping times can be excessive as can be the import costs. Also, if I haven't made it clear, I'm volunteering at a charity. No saving spared on a job.

[reformatt]

Main power rail shorts often kill one of the input MOSFET's. If either are shorted, the BQ IC will disable charging. Pretty sure this info is in one of Piernov's sticky's at the top of the sub. This circuit uses a BQ24781, but you can use the BQ24780S datasheet to get an understanding of the function of ACFET/RBFET.

This is a beefy design so has dual MOSFET's for ACFET/RBFET. Lower wattage designs in regular lappies would shut down the power adaptor in the event of this kind of short on the main power rail, but these gaming systems keep pumping in the power hence why the cap was destroyed.

You should be checking PQB11/PQB18 and PQB12/PQB19. Unfortunately, my experience in gaming systems is that if one of these goes short, it often welds itself to the board in the process and in some cases, carbonises the PCB as well.

[CPUFiddler]

PQB11 is reading zero ohms in circuit. At this point, having informed my manager, he has declared the board BER and to stop attempts to repair it. I've located a replacement board - only £1,800 - so, nah, not happening.

Unfortunately, the story ends here.


Thank you Mon2 and Reformatt for your help.