Acer 5742G Power only on battery.

[eukal]

Hello i have a weird problem on an Acer 5742G. The laptop start and work perfectly on battery. But on ac adapter only i can't power it on. I have make a lot of test and check but i can found the problem. But at the beginning i have found corrosion on and around the PU18. I have clean the area but same problem. I have replace some cap that have not the good resistance and also replace the pu 18 and PD1 but same problem. If i check the PL27 and PL28 on battery i have fixed voltage 3 and 5v (always volatge) but on ac adapter the voltage run from 2 to 3v and 3 to 5v constantly. Because i have an other board like this i have replace the 3v/5v chip PU16 because when i plug the adapter it's seems there is an shortcut, same with PQ46 and also it have a ugly face. I have try to replace the 2 first mosfet PQ51 and PQ52 because i have 19v on first, 18.85v betwen and on the gate of PQ51 and after pq52 i have voltage that oscilate between 7 and 9v. For now i have no idee what i can check. Could you please help me ?

[piernov]

Re: Acer 5742G Power only on battery.

https://www.badcaps.net/forum/showthread.php?t=90356

[eukal]

Re: Acer 5742G Power only on battery.

https://www.badcaps.net/forum/showthread.php?t=90356

Thanks For the info. Is there a section i have to read for my problem ?

[mon2]

Re: Acer 5742G Power only on battery.

Review the operation of your 2 x DCin mosfets.

These are P-channel mosfets so the gate voltage needs to be more negative / lower than the voltage they are passing.

The gate voltage appears to be ok but is not working properly for PQ52.

Remove all power -> check the resistance to ground for PQ52, pin 5-6-7-8 (pick any one to test); meter on one pin and other meter to ground.

What is the resistance ? If the resistance is not too low, the load on the logic board is ok and the ~19v should travel through.

With no power -> meter in resistance mode -> check the resistance of each mosfet as follows:

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 and the scale used on your meter for these tests. If the resistance is low, the mosfet is defective and must be replaced.

[eukal]

Re: Acer 5742G Power only on battery.

Review the operation of your 2 x DCin mosfets.

These are P-channel mosfets so the gate voltage needs to be more negative / lower than the voltage they are passing.

The gate voltage appears to be ok but is not working properly for PQ52.

Remove all power -> check the resistance to ground for PQ52, pin 5-6-7-8 (pick any one to test); meter on one pin and other meter to ground.

What is the resistance ? If the resistance is not too low, the load on the logic board is ok and the ~19v should travel through.

With no power -> meter in resistance mode -> check the resistance of each mosfet as follows:

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 and the scale used on your meter for these tests. If the resistance is low, the mosfet is defective and must be replaced.

Hello thanks for the answer, here is the value.

PQ52 drain to ground = 2.24M (meter on 200M) but if il let the meter apply the value decrease a little

PQ52
source (1-2-3) & drain (5-6-7-8) red to black give 2.20M (meter on 200M)
source (1-2-3) & gate (4) red to black give 2.43M (meter on 200M)
gate (4) & drain (5-6-7-8) red to black give 0.20M (meter on 200M)

PQ51
source (1-2-3) & drain (5-6-7-8) black to red give 1.28M (meter on 200m)
source (1-2-3) & gate (4) black to red give 0.20M (meter on 200m)
gate (4) & drain (5-6-7-8) black to red give 1.68M (meter on 200m)

[eukal]

Re: Acer 5742G Power only on battery.

Here is more info, the voltage of PU18 ( i have replace it but same )

1 0.117v
2 3.248v
3 0.910v
4 0.000v
5 3.7 to 4.6 oscilating
6 3.240v
7 3.5 to 4.9v oscilating
8 18.652v

i think the oscilating voltage is the problem and if i check resistance of components near (like PR389) just after unplug the power the resistance is very high and take many time to decrease to normal value. Is this normal (for info this is the zone of liquid damage)?

[mon2]

Re: Acer 5742G Power only on battery.

Remove all power -> meter in resistance mode.

Confirm the resistance from the current limit resistor @ PR351 to pin 19 of PU17. What is the resistance ?

Confirm the resistance from the current limit resistor @ PR351 to pin 20 of PU17. What is the resistance ?

From the schematics, the resistance of each leg must be ~20 ohms else the charger IC will believe something is wrong and will shut down the mosfets.

Although the same gate voltage is driving also the PQ51 mosfet - does it not oscillate like PQ52 ? Do confirm that the mosfets are soldered in properly.

We recently wasted too much time in repairing an iMAC 5K (another shop gave up on it) -> we found the bad boy shorted cap but did not solder back the removed dual mosfet correctly. While checking with our needle like probes, the component moved !! The PCBs are multilayer and can sink temps quickly so be sure to apply ample flux and heat. Full details of the iMAC repair to follow soon.

Review the voltages on charger IC @ PU17. Post the measurements of each pin - proceed with extra caution so that the pins are not shorted.

The mosfets look to be ok.

[eukal]

Re: Acer 5742G Power only on battery.

Thanks again, here is the mesure you asked me :

@PR351 to pin 19 of PU17 is 2.30 ohms (meter on 200 ohms)
@PR351 to pin 20 of PU17 is 20.04 ohms (meter on 200 ohms)
PU17
1 0.006v
2 0.083v
3 0.001v
4 0.006v
5 0.071v
6 0.017v
7 0.150v
8 0.001v
9 0.001v
10 0.001v
11 0.001v
12 0.001v
13 0.001v
14 0.114v
15 0.006v
16 7.4 to 9.7v oscillating
17 7.4 to 9.7v oscillating
18 7.8 to 10.0v oscillating
19 7.6 to 10.0 oscillating
20 7.6 to 10.0 oscillating
21 7.5 to 9.7 oscillating
22 7.6 to 9.4 oscillating
23 0.284v
24 0.001v

I send you the PQ51 and 52 voltage right after diner.

[mon2]

Re: Acer 5742G Power only on battery.

24 0.001v

So,

1) PU17 charger IC is not being powered (pin 24).

2) See attached. For PU17 to be powered:

a) see attached datasheet for this IC.

b) power to this ic is only if mosfet PQ54 is on

c) PQ54 will be on only if the gate is a negative (lower) voltage that it is passing

d) gate will be lower only if PQ55 is on

e) PQ55 will be on only if gate is a high voltage

f) gate will be a high voltage only if one of the diodes inside PD10 is conducting

g) PD10 is linked to the GPIO pins of U32 (KB926QFD3_LQFP128_14X14)

If U32 is flash based - consider to reflash it.

Review the voltages of the above trail. Post your measurements.

[eukal]

Re: Acer 5742G Power only on battery.

So,

1) PU17 charger IC is not being powered (pin 24).

2) See attached. For PU17 to be powered:

a) see attached datasheet for this IC.

b) power to this ic is only if mosfet PQ54 is on

c) PQ54 will be on only if the gate is a negative (lower) voltage that it is passing

d) gate will be lower only if PQ55 is on

e) PQ55 will be on only if gate is a high voltage

f) gate will be a high voltage only if one of the diodes inside PD10 is conducting

g) PD10 is linked to the GPIO pins of U32 (KB926QFD3_LQFP128_14X14)

If U32 is flash based - consider to reflash it.

Review the voltages of the above trail. Post your measurements.

Thanks again. So there is mesurment of pq54, PQ55, PD10. I'm afraid that there is always this volatge oscilating. I see another post in this forum where the guy have quite the same problem of me and the oscilating votage is gone after a capacitor replacement near PU18, like you say my PU18 have water damage too so possibly same problem ? I have no the programer for the U32 but i have another board with same component but la-5893p instead od la-5891p ( both board is 5742 )

PQ54
1 0.001v ( many time when i just plug the probe i get 0,2v to0.6v but in 2-3 seconds it drop to 0.001v )
2 7.6v to 10.00v oscilating
3 7.6v to 10.00v oscilating

PQ55
1 7.5 to 9.8v oscilatingv
2 0.006v
3 0.001v

PD10
1 0.004v
2 0.002v
3 0.003v

And also the voltage of PQ51 and PQ52
Voltage
PQ51
5-6-7-8 = 19.332v
1-2-3 = 18.842v
4 = 18.838v

PQ52
1-2-3 = 18.842
4 = 18.838v
5-6-7-8 = 7.6 to 9.9v (with the charged battery plug i have fixed 11.386v and i can power on the laptop)

I think the problem is from oscilating voltage but why ???

[eukal]

Re: Acer 5742G Power only on battery.

Another info, i have check with a thermal cam and found a part of the board a little more hot ( on the other board i have not this case ) And this part is right underneath the part with PU18 that have water damage so it could be the reason of oscilating voltage. But i doesn't found shortcut on this 2 area.

[eukal]

Re: Acer 5742G Power only on battery.

So now because of my last message, i decide to made the replacement of

PR301
PR298
PR297

Now i have on
PU18
1 3.178v
2 3.247v
3 3.684v
4 0.001v
5 2.251v
6 3.240v
7 0.025v (not normal this time i think)
8 18.677v

and

Voltage
PQ51
5-6-7-8 = 19.340v
1-2-3 = 18.852v
4 = 18.848v

PQ52
1-2-3 = 18.852
4 = 18.848v
5-6-7-8 = 18.542v
It's seems good this time

But not resolve and new symptoms

So the laptop boot already if battery present but not if i plug the adapter. If i just plug the battery i can power on the laptop and if i plug the adapter after the laptop stay on and the battery charging led appear. At this moment if i unplug the battery the laptop stay on.

[mon2]

Re: Acer 5742G Power only on battery.

Can you remove the battery and use only the adapter?

Then share the mosfet voltage readings.

As these are p-channel mosfets, the gate needs to be lower to enable.

[eukal]

Re: Acer 5742G Power only on battery.

Can you remove the battery and use only the adapter?

Then share the mosfet voltage readings.

As these are p-channel mosfets, the gate needs to be lower to enable.

So yes i can unplug the battery ( step is to plug the battery, power on the laptop, plug the adapter then light of charging appear, then unplug battery and the laptop continue working.
And there is the voltage, this time it's good but i can let the laptop like this.

Voltage
PQ51
5-6-7-8 = 19.035v
1-2-3 = 19.025v
4 = 8.081v

PQ52
1-2-3 = 19.025
4 = 8.081v
5-6-7-8 = 19.013v

[eukal]

Re: Acer 5742G Power only on battery.

Oh and for info if i plug both the battery and the adapter , i can't power on the laptop this time. Previously before replacing the capacitor i can start with both battery and adapter but remember i have voltage after PQ52 that oscilate between 7 and 9v +-.

[mon2]

Re: Acer 5742G Power only on battery.

These are now good voltage readings on the DCin mosfets.

If you leave the battery disconnected, the laptop works fine with the adapter?

[eukal]

Re: Acer 5742G Power only on battery.

These are now good voltage readings on the DCin mosfets.

If you leave the battery disconnected, the laptop works fine with the adapter?

Yes it work fine but i have to start the laptop with only the battery before, then plug the adapter and after that unplug the battery.

And like i say just the message before, if i plug the battery and the cable i can't start the laptop, i have to start with only the battery or it's not power on

So i can't let the laptop in that state.

[mon2]

Re: Acer 5742G Power only on battery.

With only the power adapter, measure the voltages on each pin of pu17. The gate voltage is correct when the adapter only is used. We need to confirm the other voltages are as well.

After the above measurements, remove all power. Meter in resistance mode. Check the resistance of the mosfet pins, like before, for the high and low side battery charger mosfets. Post the readings.

[eukal]

Re: Acer 5742G Power only on battery.

Here is the voltage, i want to tell one more time i can get the good gate voltage only if i start the laptop whit the method i tell you so first plug the battery, then start the laptop, then plug adapter, then remove battery. If i just plug the adapter whitout this procedure i have gate voltage at 18.8v and the laptop no start and no charging led.

So
laptop start ( battery plug, power on, plug adapter, unplug battery )
0.399v
0.173v
0.000v
0.009v
0.002v
0.002v
0.003v
0.000v
0.000v
0.000v
0.000v
0.000v

0.000v
0.248v
0.369v
0.564v
0.835v
0.783v
19.018v
18.990v
0.760v
0.772v
0.761v
1.4 to 1.7v oscillating

laptop not started and just adapter plug
0.002v
0.042v
0.001v
0.002v
0.089v
0.044v
0.003v
0.000v
0.000v
0.000v
0.000v
0.000v

0.000v
0.117v
0.001v
0.010v
0.454v
18.665
18.663v
0.100v
0.098v
0.748v
0.004v
I check the résistance now

[eukal]

Re: Acer 5742G Power only on battery.

With only the power adapter, measure the voltages on each pin of pu17. The gate voltage is correct when the adapter only is used. We need to confirm the other voltages are as well.

After the above measurements, remove all power. Meter in resistance mode. Check the resistance of the mosfet pins, like before, for the high and low side battery charger mosfets. Post the readings.

Excuse me but where are the highside and low side battery charger mosfet ?

Thanks