Hi guys.about a month ago I had a backlight issue on my l745 laptop.i searched for answers all over the Internet including here.i was finally able to resolve the issue.here is how I solved it.incase someone else needs the tutorial.
I searched the whole board and all fuses are intact.none burnt.i should add here that the problem started when I stupidly removed the lcd cable with the battery still attached to the system.i got an info online on how to check currents on the lcd.according to your schematics four point should majorly av power.vcc 3v,pwd and led enabler should have 5v but in my case they should av 3v(the schematics won't state that part and that's where I missed it initially).then you should av vin of about 15-20v.i opened up the led lcd of the laptop and with the lcd connected I checked vcc and found 3v.vin also had close to 19v.but pwm and led enabler had no current.so initially used a wire to pick up 5v from the external vga section of the board and connected to the pwm and led enabler(I short them and took power to one)immediately both had 5v the display light came on and I could see what's on the lcd again.i,was very happy .the display light was too bright so I went for the schematics of the led lcd and found out it needed 3v not 5v as used in lots of led lcd.so I picked up 3v from another point on the board and the lcd was not too bright.then I decded to just connect it according to the picture I uploaded so that the point where the lcd picks up the pins for the led enabler on board and pwm on board gets the 3v instead of connecting directly to lcd which can be cumbersome.with that the lcd Is working perfectly and I can now see what's on screen,of course there was a price to pay as I can not use the pwm to regulate the backlight anymore so the backlight stays at 100 percent irrespective of the laptop settings which means that the lcd runs at highest power with battery hereby leading to more power consumption.but it's better I get 100 percent power and backlight than no working laptop.ill upload pictures of the board before and after the job is done provided I av the capacity to upload here.i just made this tutorial Incase someone else needs it.let me also add that vcc turns on Ur led lcd so if no 3v there Ur lcd won't even turn on at all even though Ur laptop is displaying on an external monitor.hope it helps someone.
I searched the whole board and all fuses are intact.none burnt.i should add here that the problem started when I stupidly removed the lcd cable with the battery still attached to the system.i got an info online on how to check currents on the lcd.according to your schematics four point should majorly av power.vcc 3v,pwd and led enabler should have 5v but in my case they should av 3v(the schematics won't state that part and that's where I missed it initially).then you should av vin of about 15-20v.i opened up the led lcd of the laptop and with the lcd connected I checked vcc and found 3v.vin also had close to 19v.but pwm and led enabler had no current.so initially used a wire to pick up 5v from the external vga section of the board and connected to the pwm and led enabler(I short them and took power to one)immediately both had 5v the display light came on and I could see what's on the lcd again.i,was very happy .the display light was too bright so I went for the schematics of the led lcd and found out it needed 3v not 5v as used in lots of led lcd.so I picked up 3v from another point on the board and the lcd was not too bright.then I decded to just connect it according to the picture I uploaded so that the point where the lcd picks up the pins for the led enabler on board and pwm on board gets the 3v instead of connecting directly to lcd which can be cumbersome.with that the lcd Is working perfectly and I can now see what's on screen,of course there was a price to pay as I can not use the pwm to regulate the backlight anymore so the backlight stays at 100 percent irrespective of the laptop settings which means that the lcd runs at highest power with battery hereby leading to more power consumption.but it's better I get 100 percent power and backlight than no working laptop.ill upload pictures of the board before and after the job is done provided I av the capacity to upload here.i just made this tutorial Incase someone else needs it.let me also add that vcc turns on Ur led lcd so if no 3v there Ur lcd won't even turn on at all even though Ur laptop is displaying on an external monitor.hope it helps someone.
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