Acer Nitro 5 motherboard no power (FH52M LA-J891P)

[aico60]

Hello everyone,

Initially I bought the laptop with no screen issue. It was powering up without any signal to the display (neither internal, nor HDMI).

I started taking some measurements across the board, when I accidentally shorted something and heard a little clicking noise. Laptop wasn't powering on afterwards.

I bought a thermal camera and a power supply to try to find the short.
I was measuring it on the output of the resistors that are placed right after the second power MOSFET (pic1.jpg attached).
I injected voltage there and replaced the chip that was getting warm (pic2edt.jpg) and the short is gone now.

However, when I plug in the motherboard. I am not getting 19 volts from the first mosfet's src and not getting anything on gate. Drain is receiving 19V.
At the back side of the board, there are 1 cap and a resistor, ordered in the following way (pic3edt.jpg attached):

1. Voltage going from drain of the first mosfet to the cap
2. Measuring about 0.3V at the cap's output, which goes to the resistor
3. Resistor's output is connected to the 1st moset's 4th pin (gate)

So the first mosfet is not really getting activated because there is almost no voltage on its gate.
I have read that capacitors are supposed to not pass the voltage.
Is it possible that the schematics is wrong?
If I remember correctly, I was measuring about 25V on gate pin before. (might be wrong though).
I have checked those mosfets and all of them are getting activated when I inject voltage to the gate.
Right now, the small mosfet is removed for testing purposes.
I am attaching a screenshot of the schematics and a boardview of the output of the capacitor I mentioned in point 2 above.
Please note that the motherboard never had mosfets on the bottom side (PQB18 and PQB19, there are mosfets only on the top PQB11 and PQB12)

Any advice on how to proceed and what to check is welcome.
If more information is required, please let me know.


Thank you and regards.

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Remove PRB7 4k resistor. Do not lose it.

Then power up again and measure the voltage to ground of the ACDRV pin on the charger IC.

Post your measurement.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Hello,

Thanks for your fast response.
I have removed the resistor and the measurement starts dropping from about 0.100 to 0.001V rapidly as soon as I touch the positive probe on pin 1 of the resistor, as well as gate pin (4) on the mosfets PQB11 and PQB12. (as they are connected according to the schematics and the boardview). Drain of PQB11 measuring at 0.010V and drain of PQB12 measuring at 0.036V.

I can also provide boardview and schematics if it will help.

Thanks and regards.

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Yes, do post the schematic & BV files.

If you have 0v on drain on PQB11, this means your adapter is not supply the required 19v. Can you confirm this measurement to ground again ?

DRAIN pins = 5-6-7-8 (they will be grouped together).

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Hello,

Sorry, my bad for PQB11, drain is 19.5V, the AC adapter is good.
I meant to say that source on PQB11 is 0, as well as gate on both mosfets + drain on PQB12.

Attaching schematics and boardview.
Note: Schematics is for rev 0.1 as I could not find one for REV 1A (but there are some changes noted at the bottom of the file so might contain components for rev 1A)

[MOD EDIT] Link to Schematics & Boardview -> https://www.badcaps.net/forum/troubl...atic-boardview

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

With the gate pin floating, since the ACDRV resistor is removed, the gate voltage is 0 volts. For the mosfet to be ON (N-channel type), the gate voltage has to be higher than the voltage being passed between source and drain.

So the results are normal.

With the ACDRV resistor removed, what is the ACDRV pin voltage to ground on the charger IC pin?

Is it ~25v ? If not, measure REGN pin voltage to ground.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Both pins for the PRB7 are almost 0 volts. One being 0.001V and the other being 0.008V.
Attaching screenshot for better explanation.
REGN voltage is 6 volts. Attaching screenshot for it too.

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Check the voltage to ground of the ACOK pin on this charger IC.

It appears the charger IC is defective but measure the above to confirm.

If there is no shorted part on the main 19v rail, you could inject it with a dc power supply for testing. Limit the current to a safe value. Post the measurements.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

The ACOK pin on PUB1 (charging IC) outputs 0.023V.
Where would you suggest to inject the voltage? And how many volts to inject?

I could try to swap the IC if that does not work, the donor board I have is from another Nitro 5, so the IC chip is the same one. Just checked the schematics.

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

The ACOK pin on PUB1 (charging IC) outputs 0.023V.

Is this with the power adapter connected?

If yes, this signal is not working properly.

Confirm the voltage to ground of ACDET pin on PUB1 charger IC.

If ACDET is too low, then ACOK will be pulled to a logic low.

Confirm the voltage on the attached resistors that define the voltage of ACPRN_CHGR pin.

What is the voltage on each side of PRB32 ?

No injection, for now.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

All measurements are taken with the power adapter connected and no battery connected.
ACDET on PUB1 is 2.65V.
PRB32 is 0.023V volts on the side connected to the IC chip and 6V on the other side.

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Remove all power. Meter in resistance mode.

Measure the resistance of PRB32. Is it ~10k ohms ? Be sure that this resistor is properly soldered onto the board.

Next, measure the resistance to ground of the ACOK pin. What is the measurement?

If the ACDET pin is > 2v4 AND the adapter voltage is not exceeding ACOVP = 26v then ACOK should be floating = High Impedance. Only then will the pull-up resistor PRB32 be required to soft pull-up this line to a logic high state.

That is, ACDET is an open drain pin. If any of the above checks fail, then ACDET will be pulled DOWN by the charger IC to a logic LOW level.

Interesting reading:

https://e2e.ti.com/support/power-man...81-description

Datasheet for the BQ24780S (public IC from TI) is attached.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

PRB32 is about 10k Ohms.
ACOK is 11.6k Ohms to ground.
The charging adapter is about 19.5V.

The IC chip is getting 19.3V on pin 28 (VCC).

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

All looks to be fine. We are trying to determine if the charger pin is releasing this line, as it should, under these conditions. Then this ACOK should be a logic high but it is not. Or are external components pulling down this same line but the resistance is not low.

What is the voltage to ground value of the SRN pin on the charge IC ?

Check to see if you have resistors PRB34 and PRB35. If yes, remove them both and leave in only the pull-up resistor @ PRB32 (10k).

Then test again to see if ACOK returns to the expected value.

If it does not, suggest to replace the charger IC.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

SRN pin has 0.136V.
As the original design does have PRB34 and PRB35, I will try to replace the IC chip directly. It is a pain to solder and de-solder those little resistors and it will be a lot easier to replace the ic chip itself.

By the way, I just remembered that when I initially found the shorted chip and removed it, after that the resistance on PRB3 and PRB46 (where I was measuring the short, screenshot attached - low_res.png) was low again, about 100 Ohms, which seemed odd.
I injected voltage on that pin again and something in the bottom right area on the top of the board was getting warm. I am not sure what it was, since the thermal camera I am using is Flir One and I cannot see the exact heating component.
After a couple of seconds, something popped and the short disappeared. The faulty component might have burned. Attaching screenshot of the area (heated area.png). Since it is the battery area, would it affect the IC chip's readings, eventually the output? No battery was attached at this time.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Edit:

Replaced the IC chip. 25V are now existing on the mosfet gate pins.
Thank you very much mon2!

I will try to proceed with the board and let you know what happens.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Hello,

The laptop is now at the state where it was before I mistakenly shorted it.
It starts spinning the fans and keyboard lights up, but there is no display.

I tried taking some measurements and found out that DRAMRST is only 118 mV with RAM inserted and about the same when RAM is removed, which appears to be odd as per my readings.
The ram is also getting 1.2V, which I have measured too.

Unfortunately, I am not sure where to look for for this issue.
Could someone please guide me?

I have already tried cleaning the bios and also flashing a new one after downloading from Acer site and extracting the bin. The results are the same.

Edit:

Measured some pins of PUG1 (attached screenshot):
pin 1 - 5V
pin 3 - 4.8V
pin 5 - 0V
pin 7 - 0V
pin 8 - 0V

Is it possible that DRAMRST is low because the CPU is not getting power from PUG1?

PLT_RST is 3.3V.

Thank you!

[mon2]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

From another thread...

DRAMRST# will be pulled low if bios is corrupt.

[aico60]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Hello,

Thanks for the update. I have encountered this post as well, however it looks like it is not BIOS related in my case. I have tried to clean it again but no luck. Still missing DRAMRST.
Could it be related to the PUG1 not powering the mosfet for VCCGT/+VCCSA?

[Sephir0th]

Re: Acer Nitro 5 motherboard no power (FH52M LA-J891P)

Missing DRAMRST# can have various possible reasons. If BIOS can't solve it, you're immediately out of luck since it points to a issue with either the PCH or the CPU. Of course after the "simple" things already were ruled out.
Personally I solved a low DRAMRST# on a Razer Blade once, by replacing the PCH. It was of course a mess till I reached this point.