Lenovo G70 Screen backlight

[Bibbles]

Hi, i have an issue with a Lenovo G70. It has had liquid spilled on it and as a result there was corrosion over the components in photo. At first the screen would brighten when the on screen slider was pulled into the dimmest position and dim when the slider was pushed in the opposite position. After cleaning the area with isopropyl alcohol and a soft cloth very gently the screen is permanently dull and no adjustment is possible. On the other side of the board from the damaged area is the screen cable so i am assuming that the components relate in some way to the screen issue. I think it may be a damaged / blown fuse. Could i ask if anyone could help in identifying the components and whether the issue is in fact anything to do with a fuse or otherwise.

Thank you in advance.
Regards Dave

[VaNDAL_UK]

Re: Lenovo G70 Screen backlight

The fuse is the one with a 0 on it.

[Bibbles]

Re: Lenovo G70 Screen backlight

Thanks for the quick reply, have tested and there is continuity? Cant be that that's the problem. I was thinking it was the one next to the arrow as this doesn't have continuity. Have you any iseas what may be causing the issue?

[cyberhack]

Re: Lenovo G70 Screen backlight

That's a cap and clean up the board i have added a schematic goto page33
and check.

[Bibbles]

Re: Lenovo G70 Screen backlight

That's a cap and clean up the board i have added a schematic goto page33
and check.

Thank you. As i am a complete novice and cant read the drawing you provided, i wondered from the information i have given in my original request whether you could offer identification of the parts in the photo and what reading they should have if they were working correctly. I hoped the fact that the brightness worked in reverse prior to cleaning may give a qualified person a clue.

Regards Dave

[meritosari]

Re: Lenovo G70 Screen backlight

If C15 have short/contiunity from pin 1 to pin 2, there is a chance R17 has open. B+ is Main voltage from AC/DC. from adapter 19V, from Battery 12V (depend value rate in battery case)

clean the board, remove and check C15, don't forget to check contiunity to the pad of C15 as well. if shorted has gone, replace R17 (if already open)

[Bibbles]

Re: Lenovo G70 Screen backlight

Thank you so very much for this information. I will have a go over the weekend.

Cheers

[Bibbles]

Re: Lenovo G70 Screen backlight

If C15 have short/contiunity from pin 1 to pin 2, there is a chance R17 has open. B+ is Main voltage from AC/DC. from adapter 19V, from Battery 12V (depend value rate in battery case)

clean the board, remove and check C15, don't forget to check contiunity to the pad of C15 as well. if shorted has gone, replace R17 (if already open)

I have thoroughly cleaned the board with isopropyl alcohol.
Hi i have checked as best i know how. I have power to both sides of R17 and continuity. I also have power to the top side of C15 Yellow arrow but none at the black arrow side or continuity. Does this help at all. PS what do you mean by remove and check C15, i can remove but what am i checking for? Thanks again for your help.

Dave

[Bibbles]

Re: Lenovo G70 Screen backlight

That's a cap and clean up the board i have added a schematic goto page33
and check.

Hi, i have done some research and had help from another forum member. I have discovered that the capacitor (C15) is giving out a reading of 560 on the 2K scale on my multimeter. Occasionally it gives out 480, but very rarely. Could i ask what is the capacitors supposed value and if not correct where would i find a replacement.

Thanks again.

[meritosari]

Re: Lenovo G70 Screen backlight

I have thoroughly cleaned the board with isopropyl alcohol.
Hi i have checked as best i know how. I have power to both sides of R17 and continuity. I also have power to the top side of C15 Yellow arrow but none at the black arrow side or continuity. Does this help at all. PS what do you mean by remove and check C15, i can remove but what am i checking for? Thanks again for your help.

Dave

So, B+/LEDVDD have no problems. Even without C15, the circuit should be working fine. Maybe the real problems was related with BKOFF# / DISPOFF# signal and INVT_PWM signal

you can read as reference here:
https://sites.google.com/site/lcd4ho...-led-backlight
https://sites.google.com/site/lcd4hobby/lvds-cables

[Bibbles]

Re: Lenovo G70 Screen backlight

So, B+/LEDVDD have no problems. Even without C15, the circuit should be working fine. Maybe the real problems was related with BKOFF# / DISPOFF# signal and INVT_PWM signal

you can read as reference here:
https://sites.google.com/site/lcd4ho...-led-backlight
https://sites.google.com/site/lcd4hobby/lvds-cables

Thank you for your help. I have been very busy sorting other work related items, i will take a look shortly and report back any results.

[MadalinJula]

Re: Lenovo G70 Screen backlight

hi,
can you help me with the bios for G70-80?
ailg1 nm-a331 rev 1.0.
Thank you in advance!
Have a nice day!