No output through lvds, only hdmi

[liquidzorch]

Hello. A client brought in a lenovo g480 for repair, it would not turn on. I flashed the bios with a clean on found here, and it now turns on. Now there is an issue with the screen. The screen it had seemed to have been removed once before (the laptop has an unknown backround), this screen had an image but all scrambled, you couldn't make out anything on the screen. So I told the client (who bought the laptop as is) that I could get it to boot but he would have to change the screen and/or lvds cable. Now he came back with a new screen and a new lvds cable and it has no image, it just lights up black. It DOES however output a perfect image through HDMI to my tv.

I have tried flashing other bios files, like a g580 file that I found here, and a confirmed working g480 bios also from here. All power up and send image through HDMI, but get no image on laptop screen. I have tried my own lcd screen, just to make sure, with old and new lvds cable, all do the same thing.

Any ideas?

ps. The computer has no operating system, I am only using post and bios settings screen. This should have no affect on the output

[mcplslg123]

Re: No output through lvds, only hdmi

Schematic is available. Why not check LVDS pin voltage and find out what is missing??

[liquidzorch]

Re: No output through lvds, only hdmi

Schematic is available. Why not check LVDS pin voltage and find out what is missing??

Every signal pin has a voltage. Most are around 3.3v, others around 1.5v. Do pins that have "clk" need to have a clocl on them? With an oscilloscope, two of the clk pins are stable at 3.3v.

[SMDFlea]

Re: No output through lvds, only hdmi

Do you know what part number the screen with the scrambled image was,and the part number of the new screen.It should be similar to LTN140AT26L01

[liquidzorch]

Re: No output through lvds, only hdmi

Do you know what part number the screen with the scrambled image was,and the part number of the new screen.It should be similar to LTN140AT26L01

Part number LTN140AT26, it gives a black screen (backlight on).
One that gives a scrambled output is: LTN140AT07.
Both work great on a Compaq CQ40 that I have here.

And as for the first one it had, I do not know what the part number was, but it also had a scrambled output.

[SMDFlea]

Re: No output through lvds, only hdmi

Part number LTN140AT26, it gives a black screen (backlight on).
One that gives a scrambled output is: LTN140AT07.
Both work great on a Compaq CQ40 that I have here.

And as for the first one it had, I do not know what the part number was, but it also had a scrambled output.

You can try and flash a lenovo EDID dump to the LTN140AT26 .The EDID is stored on a small 8 pin chip on the PCB. See post #63 here for the dump - https://www.badcaps.net/forum/showth...t=74729&page=4

[liquidzorch]

Re: No output through lvds, only hdmi

You can try and flash a lenovo EDID dump to the LTN140AT26 .The EDID is stored on a small 8 pin chip on the PCB. See post #63 here for the dump - https://www.badcaps.net/forum/showth...t=74729&page=4

Thanks. Would it be this if the screen works correctly in another laptop? I'm asking since I would have to buy a programmer just to try and flash it.

[SMDFlea]

Re: No output through lvds, only hdmi

Thanks. Would it be this if the screen works correctly in another laptop? I'm asking since I would have to buy a programmer just to try and flash it.

On some older ibm/lenovos the EDID is modified to whitelist them.Don`t you have an SPI programmer ?

.

[liquidzorch]

Re: No output through lvds, only hdmi

On some older ibm/lenovos the EDID is modified to whitelist them.Don`t you have an SPI programmer ?

.

I use a raspberry pi. I'll check to see if flashrom is compatible

[liquidzorch]

Re: No output through lvds, only hdmi

I have not found info on flashing the EDID with a raspberry pi. But I did find a LTN140AT26 l01 on another lenovo, isntalled it, but still got a black screen, so I would imagine it isn't an EDID problem.

Does the bios do any serial checks with the ec or anything? The bios files I have flashed have been as is, just downloaded the files from here and flashed. They all have worked for HDMI output.

Another issue, if I try to update the bios from windows using the original files from lenovo, When I press flash in the pheonix program, the progress bar gets to about 1/4 the way quickly and the just disappears with no message. I does not have a battery, but I would image if it was that then an error message should appear. I don't know if something else is stopping the update.

PS: the bios that is corrput was version 62cn41ww, and I flashed a 62cn44ww (currently on it). And I have tried a 62cn34ww. The ec version is 62ec30ww (havent touched that).

[SMDFlea]

Re: No output through lvds, only hdmi

Maybe the problem is with the PCH, not sure. Post a link to the schematic. The phoenix flasher might have a command line switch to bypass the battery check.

[liquidzorch]

Re: No output through lvds, only hdmi

Maybe the problem is with the PCH, not sure. Post a link to the schematic. The phoenix flasher might have a command line switch to bypass the battery check.

I got the schematic from here:
https://forum.laboneinside.com/viewt...oogle_vignette

I was thinking PCH but I don't know how to confirm it.

[liquidzorch]

Re: No output through lvds, only hdmi

Edited, useless information about lvd_ddc lines not communicating.

[liquidzorch]

Re: No output through lvds, only hdmi

Never mind. I see that there is communication occurring on the lvd_ddc lines during the first second of turning on.

Another symptom. While in windows, if I booted with the lcd plugged in, but HDMI off. I can never get HDMI to work, it never switches. The same if I boot with HDMI, and later unplug the HDMI cable, the lcd does not turn on.