Asus K43U LA-7321P power sequence issue

[jeremykum]

Hi everyone,

I need some guidance here. Hope someone can offer some explanation, out of ideas.

I have this problem with this board LA-7321P from Asus K43U.

If I insert charger first, then battery, the system is charging normally, and if I pulled out the charger, it will switch to battery power.

But if I insert back the charger, I have a short at my amp meter, goes from 0 to 2.3A and keep repeating, means power from charger is auto cut off. The system still functions though, windows won't shut down. It is still powering from battery and doesn't charge.

In short, the system must receive power from charger first. If Battery is inserted first, the supply doesn't switch over to Charger and battery doesn't charge.

I do suspect somebody else had caused some damages trying to repair this laptop. There is a bypass for direct power supply to the LVDS connector.
I already removed the bypass wire but system power is still the same symptom. I did measure the power supplied at the LVDS connector, if system in only from AC (charger), I get 18+v. If only from battery I get 12+v (only at standby, I didn't power on the board)

Here I included a schematic, refer to pg36. Hope someone can offer some guidance where should I check when charger inserted but system doesn't switch its power to AC.

[khaahk]

Re: Asus K43U LA-7321P power sequence issue

Voltages on PQ102 & PQ103 gates are doing what when the charger is auto cut-off?

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

Voltages on PQ102 & PQ103 gates are doing what when the charger is auto cut-off?

Alrite, took some measurements.

AC only
PQ102 - pin1-8 18.38V
PQ103 - pin1-4 18.38V, pin5-8 18.97V

Bat Only
PQ102 - pin1-8 12.43V
PQ103 - pin1-4 12.43V, pin5-8 0V

Bat inserted, then follow with AC-in (charger)
PQ102 - pin1-8 12.43V may skip to 13.xxV occasionally
PQ103 - pin1-4 12.43V may skip to 13.xxV occasionally
PQ103 - pin5-8 jumping between 10.xxV - 13.xxV

BTW, now I am powering with a Acbel adapter rated 65W attached to a Kyoritsu Ammeter.

Ampere reading from 0.001- 0.002 jump to 1.700 to 0.000 to 0.001 to 0.307.
It's just showing me power circuit problem.

Normal standby (battery removed) is 0.018A

Hope this helps...
Thanks for the help in advance.

[paulstef]

Re: Asus K43U LA-7321P power sequence issue

PQ103 - pin1-4 12.43V may skip to 13.xxV occasionally

So this would be always ON. Meaning the path from B+ to BATT is correct for charging.

With the error present what is the voltage at VIN, P2 and P3? That's around PQ101, PQ102. Measuring to ground.

Then what is the voltage VGS of PQ101 and PQ102? You only gave us VDS of PQ102.

[khaahk]

Re: Asus K43U LA-7321P power sequence issue

I would first try another ac adapter. Or the charging circuit (ic?) is not working correctly. PIN2 (ACSET) of ISL6251 is stable?

[atsio]

Re: Asus K43U LA-7321P power sequence issue

PQ101, PQ102, PQ103 are PNP FETS and gate (pin 4) should be low(locked in "protected mode"). Check resistance to ground on pins 1,2,3 of PQ101 and PD101. Check also PQ101, PQ102 and PQ103 if OK. If all OK measure voltage on all pins of charger and report.

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

Alrite, will check it later, need to go out deliver stuffs to client.

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

I am sorry for the late reply, had a busy day with many laptops coming in.

Now I manage to get some readings as requested;

atsio:
Battery pin when only charger inserted.
1 & 2 = 18.36v keep dropping
3 & 4 = 0v
5 & 6 = 3.327v
7 = 3.293v
8 & 9 = 0v

Is it Pin 1 & 2 should be steady at 18.36v (same as my input voltage)?

PQ101 pin 1-3 to ground 33.2Kohm
Checked all Source/Drain/Gate of PQ101/102/103 should be fine, all above 50ohm

PD101 1way 0.227v, reverse 0v
Ohm to ground 88.2Kohm and 136.4Kohm

Khaahk:
Adapter isn't an issue so far, I can confirm.

Pin2 ACSET ISL6251 when error is 0.6-0.8v jumping. Normal gives me 1.381V

Paulstef:
I am sorry, I couldn't get what exactly you mean by VGS?

When error;
VIN = 9.46-11.24V jumping up and down
PQ101 pin 5-8, I get 11.42V, and this I measure the battery voltage, it's the same.

Alrite, I think I explain the sequence.
Adapter plug in, then battery, it works fine.
I remove the adapter, it still powering the laptop.
I reinsert the adapter, my amp meter goes haywire, but laptop is still working fine from battery power.

Thanks in advance for the advice and your time here.

[paulstef]

Re: Asus K43U LA-7321P power sequence issue

Paulstef:
I am sorry, I couldn't get what exactly you mean by VGS?

When error;
VIN = 9.46-11.24V jumping up and down
PQ101 pin 5-8, I get 11.42V, and this I measure the battery voltage, it's the same.

VGS = voltage from gate to source
VDS = voltage from drain to source

This measurement is weird. On the schematic VIN = 5-8 of PQ101. I assume you meant you measure battery voltage on pins 1-3 of PQ101?

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

VGS = voltage from gate to source
VDS = voltage from drain to source

This measurement is weird. On the schematic VIN = 5-8 of PQ101. I assume you meant you measure battery voltage on pins 1-3 of PQ101?

Yes VIN = pq101 pin 5-8, should show my adapter voltage whenever adapter is inserted right?

What i meant was pin 5-8 shows voltage that is same as the battery output voltage.

Because there are a lot of plastic parts nearby this section, hot air blower to remove isl6251 isn't an option. And if I am not pretty sure if isl6251 is the culprit i would avoid putting this board in my IR rework station.

[atsio]

Re: Asus K43U LA-7321P power sequence issue

Cover them with karton tape and then aluminium. It should be allright.

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

Cover them with karton tape and then aluminium. It should be allright.

This will be a challenge to wrap it
Still have some new ISL6251, I will try replace it and see what happens. Update later.

[paulstef]

Re: Asus K43U LA-7321P power sequence issue

This will be a challenge to wrap it
Still have some new ISL6251, I will try replace it and see what happens. Update later.

A tweezer soldering iron works great for SOIC-8.

[jeremykum]

Re: Asus K43U LA-7321P power sequence issue

Yup SOIC8 I use a knife type solder tip and a tweezer.

Replaced ISL6251, same problem.
Got so annoyed, fix up the laptop again, power the adapter then insert battery. Reinstall Windows, disable all windows power saving feature and ran it till morning. Guess what, now whenever I reinsert the charger, the laptop respond normal doesn't matter in windows or after I shutdown the windows.