Lenovo G555, only external display working

[ktmmotocross]

Hello. Have this lenovo g555 with ATI igp. problem is that it display only on external. i replace aTI IGP with new working one but nothing changed.

lid sw have power. it is UMA version

[alihomee]

Re: Lenovo G555, only external display working

check lcd cable or ur screen

[ktmmotocross]

Re: Lenovo G555, only external display working

cable checked, lcd changed

[Life Goes On]

Re: Lenovo G555, only external display working

Check the connector from the cable.

[samanthban]

Re: Lenovo G555, only external display working

please post here if you have the schematic.

[ktmmotocross]

Re: Lenovo G555, only external display working

here is schematic

[atsio]

Re: Lenovo G555, only external display working

Please post voltages on lvds connector.

[ktmmotocross]

Re: Lenovo G555, only external display working

here is measurements of lvds connector

[atsio]

Re: Lenovo G555, only external display working

You seem to have a problem with KBC. Try to inject 3.3v on the dac_brig pin.

[ktmmotocross]

Re: Lenovo G555, only external display working

i just replaced kbc but nothing changed. try to inject. what is dac_brig signal for?

[ktmmotocross]

Re: Lenovo G555, only external display working

inject 3.3V but no change

[atsio]

Re: Lenovo G555, only external display working

brightness. Probably no enbkl signal.

[atsio]

Re: Lenovo G555, only external display working

Measure the signals on the screens lvds connector

[ktmmotocross]

Re: Lenovo G555, only external display working

rightness is regulated from UMA_PWM. ENBL signal is for VGA

[atsio]

Re: Lenovo G555, only external display working

I just noticed that you have an 15.6 ccfl screen (although schematic mentions led)

From an inverter datasheet:

"
There are two control signals that come form syst
em to control lamp brightness. One signal is
named DAC_BRIG, which limits curr
ent to meet LCD lamp current specification. Another one is
named PWM, which adjusts lamp br
ightness. This invert
er brightness is adjusted by PWM burst
mode. The PWM burst mode is that turning on and
off the lamp at rate of 150Hz. The effective
brightness is a function of the duty cycle.
"

ENBKL signal is raised from Northbridge and goes to KBC

[ktmmotocross]

Re: Lenovo G555, only external display working

but i dont have problem with backlight. i have problem with no lcd daa. i can turn on backlight but still no data or bad data

[ktmmotocross]

Re: Lenovo G555, only external display working

flashed bios, no change

for me it looks like bad clock signal or something like that. the image is distorted but i see that is something displaying but its lines

[atsio]

Re: Lenovo G555, only external display working

You have to remove Northbridge and check lines to lvds connector

[ktmmotocross]

Re: Lenovo G555, only external display working

Ilast time i have sb off the board i checked these connections and it was al good.
What is lcd clock frequency? Now dont have scope to chrck it.

[atsio]

Re: Lenovo G555, only external display working

What is SB has to do with GMCH_TX*** lines?