Lenovo Thinkpad L560 No backlight

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

The other way is to find out the cable connected to pin8 of LVDS pin and cut it and then apply 3v on the part of cable which goes to screen. Anotherway is to find out continuity between pin8 of LVDS and screen connector.

Hello!
Yes there is continuity between pin 8 of LVDS and screen connector.
I think that since the voltage from pin 7 and 8 is missing it's definitely mb problem, not cable or screen it self (tested many screens anyway)

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

If u r able to correctly identify the pin(on screen connector) connected to pin8 of lvds,you can inject voltage directly on screen con pin. Start with 1v and gradually go to 2v. Screen lights up??However proceed with caution as u should be 100% sure about the pin. Use a broken/damaged screen to try(backlit should be ok however). This is to avoid damage to screen.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

If u r able to correctly identify the pin(on screen connector) connected to pin8 of lvds,you can inject voltage directly on screen con pin. Start with 1v and gradually go to 2v. Screen lights up??However proceed with caution as u should be 100% sure about the pin. Use a broken/damaged screen to try(backlit should be ok however). This is to avoid damage to screen.

As i said before, i tried several screens and none of them lit up, so it's certain mb problem, not screen.
Tried 4 screens (all broken but with good backlight).

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

I know this is mb related but voltage on screen comes from mb only. Right. So if something is wrong with mb, does all the voltage reaches screen?? Got the point or its still not clear to you??

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

To be honest is still unclear since there is continuity from mb screen connector to screen lvds connector but i'll inject 3v to see if backlight comes on.

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

SAy pin8 on lvds connector on mb should be 3.3V and so if cable is ok ,this voltage will reach the screen. But if this voltage is missing on LVDS connector pin, screen will not get the voltage and hence wont work. This is what i mean to say.

You must cut the cable concerned and inject voltage on the part of the cable which goes to screen. Be sure to identify the cable correctly. Dont inject 3v directly, start with 1V and then gradually move up and do keep an eye on dc supply amp consumption. If the consumption shoots up heavily,dont proceed further. Once again reminding you to use a defective screen to test. However, backlit will not glow anything less then 2V.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

I'll try to lift the pin from mb screen connector, it's tiny but i think i can do it

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

Hello, are you sure you have an image on an external monitor? You must have 3V on pin 27 for the screen switch to be enabled. With 0V on pin 27 it is as if the screen is closed, so pin 8 is 0V.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Yes i enter bios and check all config this way.
Want to measure the pin 27 again?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Here is screenshot from bios too

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

SAy pin8 on lvds connector on mb should be 3.3V and so if cable is ok ,this voltage will reach the screen. But if this voltage is missing on LVDS connector pin, screen will not get the voltage and hence wont work. This is what i mean to say.

You must cut the cable concerned and inject voltage on the part of the cable which goes to screen. Be sure to identify the cable correctly. Dont inject 3v directly, start with 1V and then gradually move up and do keep an eye on dc supply amp consumption. If the consumption shoots up heavily,dont proceed further. Once again reminding you to use a defective screen to test. However, backlit will not glow anything less then 2V.

Probably i did a mistake last time i measured
There are 3.3v on pin 8 but 0v on pin 7 and pin 27 is @ 3.3v too

There are also several 3.3v and 20v voltages on LVDS cable connector on screen but still no backlit.

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

And what do you have on pin 26?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

No voltage @ pin 26 (116mV)

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

OK, the LID_SW1# is at 0V [116mV], to see if the problem is with the display interface or the motherboard, unplug the display connector on the motherboard and measure pin 26 again. If you have 3.3V, then the problem is on the screen interface, if not on the motherboard. If I'm wrong, someone correct me.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

When you say "display interface" you mean the screen cable or the small pcb with the miniDP on it?

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

For the moment, what value have you measured with what I asked you?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Ok got it now.
Without screen connector cable i measure 3.3v @ pin 26

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

Sorry you didn't understand what I was asking. Disconnect the cable coming from the screen, and measure the value of pin 26 on the motherboard.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

I edit previous message too late i guess.
I understand after a while and did, i disconnect the display cable from the mb and the 3.3v appear on pin 26.

[JaroTech]

Re: Lenovo Thinkpad L560 No backlight

Now the circuit you need to check is not on the schematic. You need to find what drives pin 26 on the display assembly.