Acer 7736zg No power

[Francisco.s]

Re: Acer 7736zg No power

Now I have finally found the time to start this project up again. Today I started checking it again with my dmm, and found that 1d5v_s3 is shorted to ground. 3d3v and 5v also looked suspicious, but that is something I will look at later.
I removed coil L58, and found that the short is after the coil, so I kept on removing IC:s that could be at fault, but the short didn´t go away. I removed U54, U69 and U74 but the short was still there on the 1d5v rail.
Anyone got ideas where to look next? Checking caps?

1d5v_s3 seems a high power output, (very high current) so internal resistance (impedance) is very low. Load impedance, would be very low also, so you can measure resistance of one ohm or less.
Re-check your measurement with ohmmeter, and post results.

[bollin]

Re: Acer 7736zg No power

Ok, earlier today I measured it to be around 1-2 ohm, but that could be alright then. I didn´t try to power it up, because I knew it wasn´t alright (KBC missing), and after I soldered in the new one I started checking if it seemed ok. So then the next step is to see what happens when i plug in the power cord.

[DrDale]

Re: Acer 7736zg No power

I had no lights at all, U58 fixed mine. Gate was shorted to Drain. Any idea what is the cause. (My battery is dead!) FYI I checked the other supply lines and saw around 14 ohms on one but it powered up fine. Thanks for the Info.

[Maxmad]

Re: Acer 7736zg No power

hello,

i have the same laptop.

Problem is that charger's light blinks.
there was a dead mosfet U29 just after dc plug. Mosfet was replaced but still the same problem.

there is a short between DCBATOUT and ground. Resistance is about 3 ohms.
Checked every mosfet on board and seems ok.

maybe a dead capacitor? or something else?
any help?

[atsio]

Re: Acer 7736zg No power

Give resistance to ground on all pins of U29 (of course without power supply connected).

[Maxmad]

Re: Acer 7736zg No power

thanks for your replay, here are the measurements:

pins 1-3 : 295k
pin 4 : 98k
pins 5-8 : 165k

seems ok to me...

[atsio]

Re: Acer 7736zg No power

Unsolder R291 and check which side is shorted.
Do you have a regulated power supply?

[tata123]

Re: Acer 7736zg No power

I think that it is necessary to change the IC (U58) that is a MOSFET N (SI4812BDY).

[atsio]

Re: Acer 7736zg No power

I think that it is necessary to change the IC (U58) that is a MOSFET N (SI4812BDY).

Before he changes it, he can test is if it allright and if 5v_pwr line is O.k. You know, here in Greece it is not very easy to find fets. The market is too small and nobody stocks them.

[Maxmad]

Re: Acer 7736zg No power

After unsoldering R291 the short is determined to the right side of the resistor as looking at the diagram. DCBATOUT shorts with ground. AD+_TO_SYS signal is ok.

I isolated some mosfets and caps but still the short persists.

U58 seems without any shorts on its pins too.

I am using the laptop's power adapter which blinks when plugged in. Of course when the burned U29 was missing adapter didn't blink.

I can't measure any voltages yet. As long as the short persists the system can't provide any correct voltage.
Is it a good idea to try a lab power supply without automatic short protection?

Does the DCBATOUT short is due to a failed component attached to it? Or maybe another component attached to another voltage can cause that?

[atsio]

Re: Acer 7736zg No power

Does the DCBATOUT short is due to a failed component attached to it? Or maybe another component attached to another voltage can cause that?

I think your problem is isolated on a component on the 19v line. Connect your lab power supply on the right pad of the unsoldered resistor (r291), set it to 1v and current limit to 500ma (if it is possible) and check which area is getting hot.

If nothing is getting hot, increase slowly the power up to 19v. If nothing is getting hot, increase current to 1Amp.

Check always (while you increase voltage) if north or south or gpu are getting hot. If yes stop immediately the test because probably on of the transistors working with the dc controller is shorted and high power is going to them.

[Maxmad]

Re: Acer 7736zg No power

I didn't make any safe conclusion after connecting the power supply...
The short forced the voltage to drop and the current to increase...

I tried to look any single component at the DCBATOUT line...

Guess what the fault was;

C604 or C597 was transformed from a capacitor into a 2 ohm resistor... (I desoldered group of 2-3 capacitors every time so i don't know which one of them was the faulty one.)Both was in the input of the hi-mosfet of VCC_CORE voltage.

Now motherboard boots normally and seems ok.


However i faced a "problem" with battery charging. While the amber charging led is on and the battery seems to charge, after a while this led flashes and the battery becomes hot.
System can boot normally only with battery.
In Windows 7 environment there is a warning that the battery maybe need a replacement. And only seems to charge until 36-37%.


I don't remember there was a battery problem... is there any way to test the charger ic circuit? what means that the amber charging led flashes?

[atsio]

Re: Acer 7736zg No power

Check voltage on pins 9, 10, 15, 16, 17, 18, 23, 25 of u31 while battery and power adapter are connected .

[Maxmad]

Re: Acer 7736zg No power

This is the read out of ISL88731A while battery and adapter are connected:

9 -----> 3.30 V
10 ----> 3.31 V
15 ----> 12.57 V
16 ----> 12.57 V
17 ----> 12.57 V
18 ----> 12.58 V
23 ----> 11.69 V
25 ----> 15.83 V

[atsio]

Re: Acer 7736zg No power

What is the rated capacity of your battery? Check voltage on pins 3,4,5. of battery connector with battery connected.

[Maxmad]

Re: Acer 7736zg No power

It is a 10.8 V battery.

Voltage on
pin 3--> 3.15-3.30 (pulse?)
pin 4--> 3.15-3.30(pulse?)
pin 5 --> 0.33
pin 6,7--> 12.58

with battery and adapter connected. seems normal?

[atsio]

Re: Acer 7736zg No power

What is the voltage of your battery (measure on pins 6,7 without power supply connected and without power button pressed)

[Maxmad]

Re: Acer 7736zg No power

12.17 V on pins 6,7
3.3 V stable at pins 3,4
0.33 V pin 5

[atsio]

Re: Acer 7736zg No power

Your charger seem to be working fine and your battery is full. Let it run to drain and recharge battery a few times and probably it will be allright.

[bruno504]

Re: Acer 7736zg No power

My experience: check for shorted transistors U64, U59, U63 and U58; check U62 power chip controller, if it has a little hole, burned or getting very hot!
If after all this checked and replaced, it burns again or getting shorted again, its ICH9M (southbridge) that is short circuited !!! Must had more than 20ohm from +3,3V to ground.