Acer 5742G Black screen

[John_F_L]

Hello,

I have an Acer Aspire 5742G (LA-5891P motherboard), which about two months ago I reballedthe graphics card and came back with a problem that does not show on the screen (then it was showing lines).
Just to be sure, I changed the chip with a new one.
Before changing it, the laptop did not even show on an external screen, now it does, but nothing on the laptops, not even the inverter lights up.

I've already tried another screen but nothing changed. I don't have a LCD cable to test test, I have to order it. Is it possible to be the cable, or look back on the BGA?
What has surprised me of course is that at pin 5,6 of the lcd connector where is + LCDVDD I measure 0V, while on + LCDVDD_R (pin 4) I have 3.3V and in TXOUT and TXCLK 1.2V it drops back to 0 and goes up again the 1.2V.

[mielta]

Re: Acer 5742G Black screen

Hi
Please mesure on R279
and mesure on PIn123 at LCD Connector

[John_F_L]

Re: Acer 5742G Black screen

R279 is 0V but R279 is for RAM. If you meant R729 (just under the connector) it is not there, but when I put it on (0ohm), nothing changed.
pin 1,2,3 is 19,4V.

[mielta]

Re: Acer 5742G Black screen

Pin 4,5,6 there must be 3,3V at least

[John_F_L]

Re: Acer 5742G Black screen

pin 4 is 3,3V.
pin 5,6 0.
source on both q28 and q30 is 0V, gate 3,3V and of course drain is 0V (I think there should be something on source)
when I press the power button source on q30 goes to 3.3V but 0 on the drain again.

[John_F_L]

Re: Acer 5742G Black screen

just to mention, when I put the 0ohm resistor r729 the voltage on pin 4 becomes 0V instead of 3.3V that is right now.

[mielta]

Re: Acer 5742G Black screen

Check ENVDD on Q31 whwn power on

[John_F_L]

Re: Acer 5742G Black screen

i measured that sometime ago and it was 0,3V.
right now it is 0V.

[mielta]

Re: Acer 5742G Black screen

Hi
I Think there is anything whis the grafikchip Signal comes from there
when it is new than reball it again

[John_F_L]

Re: Acer 5742G Black screen

I'll reball tomorrow, and tell you what will happen.

[John_F_L]

Re: Acer 5742G Black screen

I reballed the chip, the same happens. Voltage on Q31 ENVDD goes up to 56mv.

[mielta]

Re: Acer 5742G Black screen

Hi
The gate from Q30 must be lower than 3V from the source so that the voltage can be go
to the Drain
if you have an external Powersupply i Woud do 3v at the Drain of Q30 when laptop is powered on
And see what is happend

[John_F_L]

Re: Acer 5742G Black screen

I tried that and the only change is that the backlight just lights up. But still no image on the screen. On the external display the image is correct, no artifacts.

[mielta]

Re: Acer 5742G Black screen

That shows me that everything is wrong with PCH or Garfikchip
pch_envdd page16
en_vdd page22