Acer PT314-51s LA-K811P - No power on the battery

[tommy97]

Hi, i'm having problem with Acer pt314-51s - laptop stopped to work on the battery, i've got original replacement battery and it has the same issue. While battery connected, it does not show voltage on the connector on neither battery. In the system it says charging (One battery 100%, 2nd about 5%),

Laptop does work on the charger.

While charger connected:
PQB11 - Both sides 19v
PQB12 - Both sides 19v
PQB1 - LEG 5 - 19V, 1-4 0.15V
PQB2 LEG 5 - 0.15V, 1-3 GND, GATE (LG_CHGR 0.012V)

LX_CHGR - 0.15V
BST_CHGR_R - 5V
BATT_TS - 0.15V
BATT_B/I - 0.15V
EC_SMB_DA1-1 3.3V
EC_SMB_CK1-1 - 3.3V
17.v_batt+ 0.8v on the connector

[mon2]

Remove all power -> check the resistance across the battery mosfet @ PQB13.

Measure:

source (1-2-3) & drain (5-6-7-8)
source (1-2-3) & gate (4)
gate (4) & drain (5-6-7-8)

Post each measurement. If the measurement is low -> replace this mosfet and test again.

[tommy97]

source (1-2-3) & drain (5-6-7-8) - 5 M OHm - with drop
source (1-2-3) & gate (4) 2.4 M OHm
gate (4) & drain (5-6-7-8) - 3.3 M OHm - goes up

I had same mosfet for test just in case, replaced same thing.
mon2

[mon2]

Mosfet checks look ok. Connect only the battery (is it with a charge?) and check the voltage to ground of the same PQB13 mosfet.

Check source / drain / gate pins to ground. We need to confirm that the charger IC is enabling this mosfet to pass the battery voltage onto the logic board.

Are the batteries known good? Often, the battery is the root cause.

[mielta]

Hello
I Think this model has an switch to power off the Battery when cover is not installed

[tommy97]

mielta i was checking board before that however i did not find any visible button.

mon2 0v on PQB13 same as battery connector, i'm not able to confirm if battery is good but i just got 2nd one and i believe it is tested by the seller (cannot warrant that).

[mon2]

Measure the battery voltage while the battery sits on your work table. So you are measuring without any of the loading from the logic board. Would you have access to Amazon? They are good to accept returns if you do not need the battery after this exercise. Hoping there is a charge from the vendor to at least proceed with some tests. Need to confirm if the battery voltage shunts upon connection to the logic board.

[tommy97]

mon2 Hi, i've got 2nd replacement of different seller 100% genuine battery, and it did not change anything. I've noticed when battery attached batt_ts and batt_b/i from 3.3v goes to 0.5v (on charger), while only battery attached there is 0v, while charger connected 17.4V_batt++ have only 1.5V, replaced as well BQ with compatible 24780S, since that change i have 1.5V on 17.4v_batt+ where previous was about 0.5-8V. Any ideas?

[mon2]

A bit lost on the current status.

1) was an identical charger IC used for the replacement for the original?

2) it will be best to carefully measure each pin's voltage to ground on the charger IC. Post each measurement. Do connect the charger and the battery.

[tommy97]

Hi, i've replaced with different one which apparently is compatible with original from BQ24781R to 24780S

Measurements of BQ
1.18.37V
2.18.37V
3.18.97V
4.18.97V
5.1.96V
6.2.5V
7.1.5V
8.1.9V
9.0V
10.0V
11.3V
12.3V
13.0V
14.0V
15.0.155V
16.0V
17.0V
18.1.6V
19.1.6V
20.1.6V
21.1.2V
22.0V
23.1.98V
24.2.3V
25.1.6V
26.1.6V
27.1.6V
28.18.92V

[mon2]

See a number of voltage mismatches in the list.

REGN (pin #24) should be ~6 volts. Remove all power. Meter in resistance mode.

measure the resistance to ground of pin #24. Post the measurement.

is the power adapter the original and for this laptop?

ACDET is too low and must be > 2v4 on a good adapter. Double check your soldering of this part.

[tommy97]

I did re-soldered BQ and yes i can confirm REGN (pin #24) is 6V. ACDET still 2.5, i do use lab PSU i don't have original charger for it.

[mon2]

Much better. Now ACDET is in the proper range and ACDRV should follow to be a boosted voltage to enable the N-channel mosfets.

ACDRV voltage = adapter voltage + REGN voltage = ~19v + 6v = ~25 volts on a known good board.

Measure the voltage to ground of ACDRV now that the charger IC is showing the proper voltages. If ACDRV is not ~25v then flux and remove the series ~4k ohm resistor on the ACDRV line. It will reside between the charger IC pin for ACDRV and the 2 * DCin mosfets (gate pin). Do not lose this resistor.

Then power up again and check if the ACDRV voltage is present or not by measuring the charger side PCB pads where you removed the 4k resistor. Do you now have ~25 volts?

As per the above charger sticky article by piernov, often the 2nd DCin mosfet will be get killed and cause the ACDRV voltage to tank but proceed to review and post the above requested measurements.

[Sephir0th]

It should be way easier to simply measure PQB11 and PQB12 like already done with PQB13 before. It is a Standard check and should be seen like that. 19V at ACDRV is normally already proof enough for one of the DC-IN Mosfets being internal shorted.

[tommy97]

mon2 Sephir0th thanks for your advices, found out that PQB11 was a problem, replaced and now i'm getting 25v ACDRV on mosfet & bq however now laptop does not start up with connected battery (Have 2 of them for test), and still does not charge the battery, lab PSU cycling in between 0.01-2amp.

[tommy97]

Also noticed that +17.4V BATT+ , 17.4V BATT_CHG, LX_CHGR - is 5.6V with and without the battery, BATT_B/I 0.156V

[Sephir0th]

So a bootloop or charging in loop? Need to dig into the present power rails to get the clue what is going on.

[tommy97]

It have charging loop

[Sephir0th]

Are there schematics available? Usually you will find low Ohms resistors on SRN and SRP line. Find and measure them.

[mon2]

A paid website appears to have the schematics (only) from a quick Google search.

With no power -> resistance in lowest scale, measure the SRN / SRP resistance path as per the datasheet pinout for the BQ24780S. Measure directly at the charger IC.