Lenovo G580 LA-7981P

[Bibbles]

I am currently repairing a motherboard LA-7981P in a Lenovo G580. The problem i have is there is no graphics on the screen, there is light, just the normal light, not bright light like when the connectors isnt in properly. I get external graphics and laptop works normally on HDMI monitor. I have a schematic for this model and have checked the pins on LDVS connector. I have attached the page from the schematic i believe is relevant to this and a clip of the diagram where i believe i have the problem. I have voltages where they should be present apart from pin 26, this is dead, not sure what other readings i should be getting or how to check. Hoping someone will be able to help with this.

Thank you in advance

[Techtiger]

Re: Lenovo G580 LA-7981P

so you get +19V on pin 1 2 , pin 21 +3VS pin 24 +3VS pin 26 +3VS , PIN 8 ?

[Bibbles]

Re: Lenovo G580 LA-7981P

Thank you for your quick reply. Checked all above, all OK. Pin 8 =0V

[Techtiger]

Re: Lenovo G580 LA-7981P

Thank you for your quick reply. Checked all above, all OK. Pin 8 =0V

now check EDID_DATA/CLK pin 19 20 , this model needs lcd inverter if so try with another one, for the pin 8 of LVDS test R430 R431 both sides for voltage , what was the voltage on pin 22 23?

[Bibbles]

Re: Lenovo G580 LA-7981P

Pins 19 & 20 have 3.3v Pins 22 & 23 0v
This model doesnt have an inverter (A long Board under screen) or is it something on motherboard im looking for.
I do have a microscope, how do i locate R430 & R431 cant see them.
Are they visable on this photo

[Techtiger]

Re: Lenovo G580 LA-7981P

Pins 19 & 20 have 3.3v Pins 22 & 23 0v
This model doesnt have an inverter (A long Board under screen) or is it something on motherboard im looking for.
I do have a microscope, how do i locate R430 & R431 cant see them.
Are they visable on this photo

did the measurement on pin 8 22 23 was done without the screen attached ?

[Bibbles]

Re: Lenovo G580 LA-7981P

All measurements have been done without screen attached

[Techtiger]

Re: Lenovo G580 LA-7981P

All measurements have been done without screen attached

try and do measurements with the screen

[Bibbles]

Re: Lenovo G580 LA-7981P

I really appreciate the help you are giving me. I have attached a document with all the readings on with screen attached, as stated on the document the screen was continually going on and off and readings were taken in both states. Some of the readings couldn't be noted down as the fluctuation was very quick.

[Techtiger]

Re: Lenovo G580 LA-7981P

The Voltage’s Seems to be ok, either LVDS cable is bad or Screen for the LVDS cable try to test continuity with multimeter if you have spare Screen try it

[Bibbles]

Re: Lenovo G580 LA-7981P

I do have a few spare screens and they are the same, also this is a replacement cable as original was damaged. Is this flashing a symptom of a damaged cable? Testing continuity of cable and it appears that pin 1 doesn't match to pin 1 on other end neither pin 2 etc etc

Is there a diagram of cable pin mapping available