LA-791 not charge

[gcomputers]

Hello everyone
i m working from 2days with this P.bell that don t charge.

This bord is Q5WVH LA-7912P Rev 1.0 used too in Acer e-series.

I measured :
PQ9 pin5678 have 19v pin1234 no voltage

PQ10 , PQ11 no voltage
CHANGED pq9 , pq10, pq11 the same problem.

THE PROBLEM IS MISSING 3V (acok PU4 not have 3v no 3.3v on bios chip no 3.3v on pu5)

Any suggestion???

[LP_tekh]

Re: LA-791 not charge

You can share the schematic so the other can see it and share their though.

[p1muserfan]

Re: LA-791 not charge

You can share the schematic so the other can see it and share their though.

Here

[meritosari]

Re: LA-791 not charge

Seem B+ short to ground.
-check resistance B+ to ground
-check VCC voltage
-Voltage acdet should be ±2.6v

[gcomputers]

Re: LA-791 not charge

Seem B+ short to ground.
-check resistance B+ to ground
-check VCC voltage
-Voltage acdet should be ±2.6v

Thanks Meritosari
Yes B+ (measured from pd6 pin2) is SHORTED with ground voltage 09.2mv 51,8ohms
pin1 pin3 of PD6 19v stable

VCC voltage (measured from PU4 pin20) is 19v stable

ACDET is 1.38v

What can i do ?????

[angel-boy]

Re: LA-791 not charge

insert adapter or insert 1v-2v between pd6 pin2 to ground and check parts that will heat up. quickly remove if smoke will come up
with this method, you will quickly find the shorted component.

[LP_tekh]

Re: LA-791 not charge

Check pq11 if is bad, if is bad, remove it and check it again off the board same way like the other shorted components.

[gcomputers]

Re: LA-791 not charge

insert adapter or insert 1v-2v between pd6 pin2 to ground and check parts that will heat up. quickly remove if smoke will come up
with this method, you will quickly find the shorted component.

tested it, inserted with power supply lab 1v 7a and PD1 it heats up a little removed it tested with diode mode are ok , but the same problem do not charge.

[gcomputers]

Re: LA-791 not charge

all line from PQ11 pin5678 from PQ12 pin5678 are shorted with ground .

Replaced PQ11 the same problem removed PQ12 to test it no change the short continue.

Yesterday received another acer with the same board (la-791) with identical problem not charge , same short .

What can i do any suggestion ?

[LP_tekh]

Re: LA-791 not charge

May be there is no communication between BQ24725ARGRR and KBC 128pin, so either BQ or 128pin is bad, if all components connected to B+ rail are good.
I know is a lot of work to do, but you have to try to find out.

[dj_ricoh]

Re: LA-791 not charge

all line from PQ11 pin5678 from PQ12 pin5678 are shorted with ground .

Replaced PQ11 the same problem removed PQ12 to test it no change the short continue.

Yesterday received another acer with the same board (la-791) with identical problem not charge , same short .

What can i do any suggestion ?

Diode mode?

Ohm mode only . if it shows value on both sides then its bad. It leaks.

In order to find that shorth, guessing it's a cap you need to pass 2.5v on psu lab with 1-2 amps.

I repair 2 HP's and 2 Sony vaio with almost 4 v and 1.5amps.

It heated those caps so I can find them and voila they all work.

[gcomputers]

Re: LA-791 not charge

Thanks Dj ricoh , i checked the diode removed from board , i will check with your metod today. Thanks anyway

[meritosari]

Re: LA-791 not charge

try remove one by one PL that related with B+, then measure resistance after desolder one PL. PL3 PL5 PL8 and so on

[wws911]

Re: LA-791 not charge

Hi guys . i have the Same Problem .
1. i charged the batt with a bench power supply.
2. when i plug the charger in then put the batt in the charger goes in to protection
3. so i plug the charger in then plug the battery in then in windows i get plugged in and charging but its not.

where should i start checking as im very new and learning .. appreciate and and all guidance
thanks in advance

[mon2]

Re: LA-791 not charge

Same logic board and schematic?

Power down / remove battery.

Meter in resistance mode.

Check and post the resistance if each mosfet starting fr the dcin jack.

You will have mosfets in this area.

What are the values for each mosfet for:

Source & drain
Source & gate
Gate & drain

[vannix]

Re: LA-791 not charge

i just repaired 2 boards la-7912p with b+ shorted to ground, and in both the problem was a ceramic capacitor 25v 4,7uf.
in this case i suggest to replace all 4.7U_0805_25V that you can find in schematic, because after a while also the others could short to gnd, as often happens in many boards that use similar capacitors.