Acer nitro 5 LA-L191P issue on 3v_en

[DeXXter]

Hello, I'm having issues with this acer nitro 5 GH53G LA-L191P, I bought it for repair and found out the problem was de BQ24781, replaced this and the laptop worked, but the battery was on 4v and didn't charge beyond that, on windows was detected, but on 0%, so I used the power supply to try to charge the battery, with the laptop off, so at some point the battery took current and I was on this for two minutes (used 14v/2a, label says 15/17v max) and after this the laptop stopped taking current and when I tried to turn it on, it doesn't.
So I measured the laptop and when plugged in I got the +3VLP (3v ldo) and with this the power button fine and working, but is like the EC is not reading the order to turn on.
So basically I got 3v/5v ldo, EC_ON (3v) and 5VALW but the EC is not giving 3V_EN to activate 3VALW and even doing a jump wire from 3v ldo onto this 3V_EN rail from the ec I got nothing, but a small change in the current from the power supply (on 20V) from 0.005mA to 0.023 but still it doesn't turn on.

I got no short, not visual damag on ec, so I'm thinking the EC (KB9052QD) or the BQ, one of those might have the issue, maybe someone has had this before? this is my first time repairing an acer nitro and facing this kind of failure, I'm not sure if this laptop need a plugged battery connected to turn on?

On the power sequence laptop don't reach 3valw







On 3v power supply 3v_en is not present.


In any case, thanks!

[pc_okay]

Hello,

Check résistance to ground (without any source Of power) on 3v_En Line and 3VALW.

Check (With power) if power button is responding when you press it ON/OFFBTN# , must pass from 3 to 0v when you press it and come back to 3v.

[DeXXter]

Hello,

Check résistance to ground (without any source Of power) on 3v_En Line and 3VALW.

Check (With power) if power button is responding when you press it ON/OFFBTN# , must pass from 3 to 0v when you press it and come back to 3v.

Hey there, I managed to fix it and yeah I had 3v on the power key going to 0 when pressing the button, and resistance was okay on 3v_en and 3valw too, the issues were two on this laptop, first, a battery lower side mosfet that had gate and source shorted, this prevented the battery from getting charged and another channel n mosfet (sot23) that was on the batt_b/i rail from the battery and was not working (vcc_rtc on gate was on). Apparently this particular laptop need his battery to start, if it doesn't detect one it just won't enable the 3v_en. So this can be pretty tricky tbh, that little mosfet was not shorted it just didn't have a value when measuring on diode mode, although it had like 11k ohm resistance. Thanks for answering. Have a nice day.

[Bios Cracker]

Hey there, I managed to fix it and yeah I had 3v on the power key going to 0 when pressing the button, and resistance was okay on 3v_en and 3valw too, the issues were two on this laptop, first, a battery lower side mosfet that had gate and source shorted, this prevented the battery from getting charged and another channel n mosfet (sot23) that was on the batt_b/i rail from the battery and was not working (vcc_rtc on gate was on). Apparently this particular laptop need his battery to start, if it doesn't detect one it just won't enable the 3v_en. So this can be pretty tricky tbh, that little mosfet was not shorted it just didn't have a value when measuring on diode mode, although it had like 11k ohm resistance. Thanks for answering. Have a nice day.

That's one of its kind logic that....laptop needs battery connected to turn on. Maybe need to look at tha Schematic for better clarity...can you share the schematic diagram pls.

[DeXXter]

That's one of its kind logic that....laptop needs battery connected to turn on. Maybe need to look at tha Schematic for better clarity...can you share the schematic diagram pls.

Couldn't upload the schematic, but I used the schematic for GH73G LA-L181P. And the faulty mosfet was pq201.

[Bios Cracker]

Couldn't upload the schematic, but I used the schematic for GH73G LA-L181P. And the faulty mosfet was pq201.

This reset circuitry is connected to EC_RST#. So maybe that is causing SIO to not trigger.

[DeXXter]

This reset circuitry is connected to EC_RST#. So maybe that is causing SIO to not trigger.

Maybe, I had 120mA from gate to drain on both ways in diode mode on that mosfet, but no short or OL.

[Bios Cracker]

Maybe, I had 120mA from gate to drain on both ways in diode mode on that mosfet, but no short or OL.

Okay

[DeXXter]

Okay

I just checked, I was wrong and the laptop does turn on without battery, although that little mosfet was the issue.

[pc_okay]

Yes good job, thanks for sharing !
I just don't understand where goes (or come from) bi_s signal under PQ201

[DeXXter]

Yes good job, thanks for sharing !
I just don't understand where goes (or come from) bi_s signal under PQ201

Thanks np, and that's apparently just ground, on the boardview and schematics it stops there, and source has continuity with ground (I measured that).

[hopkok]

Hi guys, has this board, charging IC was dead, no voltage ACP/ACN (no short in 19V line). BQ24781 replaced, I have 19V good. Fast question, no +3_VL voltage, just 176 Ohm on +3ALW, so I injected 3V to that line and PCH is heating...
My idea is took if off, check resistance and replace PCH.

Anyway have the same board (spilled one) and there is +3ALW resistance in KOhms...so my idea shoul be right, what do you think?

[Sephir0th]

It's still strange that you don't have +3VL since the enable is clearly created from the main power rail via a voltage divider. You are sure there is no additional short?

Strongly smells like a second undiagnosed issue

[hopkok]

That is why I am sharing my idea...I have VCC on PU301, tried to replace PU301...and I was on end of my ideas, I tried to replace KBC...nothing helped, so I put everything back and started from begining... I desolder +3alw solder blob to disconnect this line, but +3_VL not pressented... Do you have any idea what to meassure before I take PCH out of board?
Am I right?
+3_VL is first generated voltage, after that can by generated 5V_ALW, than EC generate 3V_EN voltage, that activate +3_ALW...
Next I am wondering, how I could have +19_VB presented on PU301 and PU501 with faulty BQ24781...shorted PDB1 could be answer, but I measured it...it is not shorted...

Any idea really appreciated, thanks for try to help...

[Sephir0th]

You said, the Charging controller was replaced. So I don't really understand the last part of the question.

[hopkok]

That was idea before BQ replacement. Generating 5V_ALW need +3_VL or not? Not sure...

[Sephir0th]

That was idea before BQ replacement. Generating 5V_ALW need +3_VL or not? Not sure...

Yes. And generating the +3VL requires presence of +19VB. So everything in order as far as I know.

[hopkok]

+RTCVCC is shorted, PCH needs to be replaced

[DeXXter]

+RTCVCC is shorted, PCH needs to be replaced

Hey, no, there was no short, it was that little 3 leg mosfet (pq201) that was faulty (it was no shorted nor OL, just the internal diode was not okay). Already fixed this laptop.

[DeXXter]

+RTCVCC is shorted, PCH needs to be replaced

Sorry, didn't read the other answers above, you had another issue 😅... and yeah usually a short on 3v is dead chipset, unless you're very lucky and the power supply is the issue (happened to me once).