Acer aspire 5742g no VGA voltage

[bgaservis]

Hi to all experts

I really strugle with this acer aspire 5742g with intel i3-370m processor and Nvidia graphics. I have attached schematics to you if you don’t have it.

Problem is there is no VGA voltage, all other voltages are ok. RSMRST is 3.3V so Bios and Kbc is ok. PLT_RST I have checked at wireless Lan connector at pin 22, and there is voltage. There is voltage at RAS,CAS,WE,CKE0,CKE1 pin’s at DIMM slots, so memory controller inside CPU is also ok.

If you look at page 50. PU998, there is VIN voltage but there is no voltage at EN pin. So I have traced VGA_ON and get to page 38 and U21.
Supply voltage is ok, but there is no DGPU_PWR_EN voltage.

I have tryed to reprogram BIOS chip and reflow PCH, with no success.

Don’t know if I’m looking at right direction.

Can anybody help me with this problem ?

Thank you very much

[Francisco.s]

Re: Acer aspire 5742g no VGA voltage

With all signals and voltages you have checked, and bios reprogrammed, the solution points to a new PCH.
Good luck.

[tiak]

Re: Acer aspire 5742g no VGA voltage

Agree with Francisco.s
But,are you checked mosfets :PQ 34,35 and 36?
Good luck

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

Thanks for reply guys.

It looks like I didn't get PLT_RST pin corectly as it is 0V
After checking system power management pins at PCH, SYS_PWROK was missing,
Next I checked U44 at pin 4 SYS_PWROK – no voltage. Pin 1 VGATE – 3.3V ; pin 2 EC_PWROK – 0V page no 15.
The resistor R632 is ok, 10Kohm but mesuring at resistor gave 0.8ohm, short somewhere. I removed U44 still short on pin 2 and pin 3.
It looks like pin 2 is conected with SIO at pin no 104. Mesuring SIO pin no 104 and ground gives below 1ohm – short.
I tryed to bypass points at U44 pin no 5 and 4, and PCH started to work, I got PLT_RST and VGA_voltage, now all voltages are here but no display since SIO don’t comunicate with Bios.

I think it’s SIO fault as EC_PWROK shouldnt be grounded or shorted ? It gives RSMRST voltage but it’s not 100% okay.

What do you think ?

[robrock1]

Re: Acer aspire 5742g no VGA voltage

do you have a diagnosis card for mini pci-x? then you could see if post is running or not. Replace 1st nvidia chip and then the kbc if possible.

[dycc]

Re: Acer aspire 5742g no VGA voltage

U21b can also be the problem as a short at pin4 can stop ec_pwrok signal

[dycc]

Re: Acer aspire 5742g no VGA voltage

power on sequence

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

U21b can also be the problem as a short at pin4 can stop ec_pwrok signal

U21 is ok, I have first checked that. At pin no 4 SYS_PWROK_1 there is 3.3V when I removed U44, will have to check that again.

Also at SIO pin no 106 WL_OFF# is shorted to ground also.

P.S. Thanks for power on sequence

[dycc]

Re: Acer aspire 5742g no VGA voltage

EC_PRWOK=SYS_POWEROK_1 because r332=0 ohm . thus a short at one will be also at the other . unless you remove r332 before check sys_powerok_1

[dycc]

Re: Acer aspire 5742g no VGA voltage

power on sequence clean picture

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

U21 pin no 4 to ground is 2.1Mohm there is no short.
At SIO pin no 104, 106, 107 is shorted.

There is no R332 as seen in picture. The line goes right and down next to the first pad somewhere else but it's not shorted ?

The second pad where should be resistor is around 3 Ohms.

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

do you have a diagnosis card for mini pci-x? then you could see if post is running or not. Replace 1st nvidia chip and then the kbc if possible.

No at hand, I'm checking Bios chip with scope...
I don't see connection of Nvidia chip with KBC EC_PWROK ?

[dycc]

Re: Acer aspire 5742g no VGA voltage

according to the picture you are right. so try replacing sio

[dycc]

Re: Acer aspire 5742g no VGA voltage

kb926 is not so hard to find .

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

Yes, I will get them in few weeks.
I will update this thread with outcome

Thanks everyone!

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

KB926 replaced, got VGA power.

But now is the problem, there is no display at LCD screen(backlight is on), but works ok on external VGA connector.

Reflashed bios and EC ROM, changed processor, memory, reflowed gpu, tyred another LCD panel no avail!

Checked TXOUT and TXCLK pins at lcd connector, seems ok, got voltage.

I'm out of ideas.

What to check next ? Have I forgotten something ?

[robrock1]

Re: Acer aspire 5742g no VGA voltage

i am sure because you reflowed the nvidia chip it has lost contact, you have to remove and reball or replace it

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

Problem was here before reflow.

Shouldn't reflow renew contacts and not loosen them ?

[robrock1]

Re: Acer aspire 5742g no VGA voltage

but before you did not have light on the display right? Sometimes reflow does not work i have it a lot, one day i reflowed a chip 3 times and finally it worked but the first 2 times the laptop was completely dead

[bgaservis]

Re: Acer aspire 5742g no VGA voltage

If you mean on backlight, then no. Backlight was ok and is ok before and after reflow.

Display has light, but no picture.