Lenovo Thinkpad L560 No backlight

[Andreasbest]

Hello!
I have a L560 here without backlight on screen, the usual suspect (F1 3A) was burnt so i replace it, 20v are passing through now and arrive to the led backlight flex but still no backlight on screen.
I tried other lcd but no backlight on them too so the fault is not on lcd.
There are no schematics available for this board so i'm blind.
Any thoughts?

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

You can refer to any thinkpad schematic with similar pinout.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Have you seen a pinout like this?��

Also one silly question, how is it possible the 20v to arrive at led flex but this to remain off??

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

LA-C422P is quite similar, i see the JEDP1 connector there too and it's identical.
Any ideas?

(Page 19 is the lcd connector)

[mon2]

Re: Lenovo Thinkpad L560 No backlight

Tested with a fresh and known good lcd cable?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Unfortunately i don't have cable for this model , that's why i want to eliminate all other possibilities before order one.
What pin should light up the backlight?

[mielta]

Re: Lenovo Thinkpad L560 No backlight

mesure pin 7 + 8 bkoff# and invpwm and write how much volt it is

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

No voltage on pin 7 and 8
Only pins with voltage are 1, 2 & 3 @20V, pin21 @ 3v and pin18 @ 3.3v

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

So your problem is mb related. Voltage on all pins listed by@mielta along with 19V is must for screen display with backlit.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

So what should i check next?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

bump

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

You need to manually trace where those pin7/8 goes. Resistance on both pin7-8?? You can try by cutting the track for pin8 on mb and then applying 3v from dc supply to LVDS connector pin and see if it works.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

The pin 8 goes to a SMD, i'll see if i can desolder it to cut the trace softly and apply 3v

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Should i measure directly @ pin 105 of U34 if the 3v are present?
Is this correct?

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Connection between U34 pin 105 and 8pin of JEDP1 is intact.
No way to cut the trace as it goes directly on inner layers of MB.
Other way?

[Vesko356]

Re: Lenovo Thinkpad L560 No backlight

Have you seen a pinout like this?��

Also one silly question, how is it possible the 20v to arrive at led flex but this to remain off??

https://www.badcaps.net/forum/showpo...5&postcount=21

Edit: Start with the basic checks - the fuses on the screen itself, on both lines 3.3V and 20V, check them first.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Yes battery removed right before the disassembling, these faults are happening only once
The fuses i manage to locate and check are:
F1 (The 20v one, was burnt and replaced the thread with 3A, now 20v passes through it)
F3
F4
F5
F7
F8
PF101
PF201

Is any of them the 3.3v one?

[Vesko356]

Re: Lenovo Thinkpad L560 No backlight

Yes battery removed right before the disassembling, these faults are happening only once

Apparently you didn't understand what I meant - I meant that 20V (if the charger is plugged into the laptop) or 12V (or as much as the battery voltage is) is fed/present to the display connector , regardless of whether the machine is running or turned off.

The fuses i manage to locate and check are:
F1 (The 20v one, was burnt and replaced the thread with 3A, now 20v passes through it)
F3
F4
F5
F7
F8
PF101
PF201

Is any of them the 3.3v one?

I said "the fuses on the screen itself" (screen pcb) - not motherboard fuses. You didn't read carefully. There are usually two fuses, one for 20V and one for 3.3V line.

[mcplslg123]

Re: Lenovo Thinkpad L560 No backlight

Connection between U34 pin 105 and 8pin of JEDP1 is intact.
No way to cut the trace as it goes directly on inner layers of MB.
Other way?

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.

[Andreasbest]

Re: Lenovo Thinkpad L560 No backlight

Apparently you didn't understand what I meant - I meant that 20V (if the charger is plugged into the laptop) or 12V (or as much as the battery voltage is) is fed/present to the display connector , regardless of whether the machine is running or turned off.





I said "the fuses on the screen itself" (screen pcb) - not motherboard fuses. You didn't read carefully. There are usually two fuses, one for 20V and one for 3.3V line.

Hello Vesko.
Yes i understand, maybe i didn't type it well.
1) i know the power from PSU and batery are present even if laptop is off in several parts, recently i destroyed a Precision 7510 this way so i got my aftermath.

2) In the previous posts i mention that i have tried several screens, none of them gave backlight (most are broken and/or with lines but backlight used to work), so i guess the voltage from 7 and 8 pin is missing from mb fault, not screens.