Lenovo Thinkpad T550 no backlight

[mytownmatt]

Hello everyone, fist post here.

I have a Lenovo Thinkpad T550 that no longer has LCD backlight after a small drop. The drop was not enough to damage the mechanical HDD, nor break the LCD.
It seems, after analyzing the schematic, boardview, and motherboard with a multimeter, that the ThinkEngine chip is supposed to produce the signal and is no longer doing so.
I am not a novice in general repair, but I am new to board level repair, so I am trying to see if anyone else has experienced this, or has knowledge of this particular board they could help point me in the right direction.

Thanks

 

[Admin]

PUT those voltage
R2901 pin2 =
U2901 pin 1,2,3 =
F2901 pin1 =
F2901 pin2 =
F2902 pin2
F2902 pin1=

 

[mytownmatt]

R2901 pin2 = 13.97v
U2901 pin 1,2,3 = 3.36v, 3.36v, 3.36v
F2901 pin1 = 3.36v
F2901 pin2 = 3.36v
F2902 pin2 = 20.2v
F2902 pin1= 0v (29mv)

 

[mytownmatt]

So, should I assume a bad fuse at F2902

I was trying to trace the signal for pins 32 and 33 on LCD1, as they are labeled backlight_on and panel_bklt_ctrl

but clearly I missed vbl20 (which I would assume needs to be present in order for backlight on / ctrl to function) as vbl20 is the main power for the LCD

 

[Admin]

So, should I assume a bad fuse at F2902

I was trying to trace the signal for pins 32 and 33 on LCD1, as they are labeled backlight_on and panel_bklt_ctrl

but clearly I missed vbl20 (which I would assume needs to be present in order for backlight on / ctrl to function) as vbl20 is the main power for the LCD

F2902 THIS FUSE it has been broken ,need to be replaced and before you do that you have to check if there is any short circuit on F2902 pin1 with and without the LVDS CABLE.

 

[mytownmatt]

Awesome, thanks!

I'll keep you posted after I complete the repair.

 

[redart]

Hi all,
Came across this post during troubleshooting of my own T550, which has also just lost it's backlight. The values from above all check out with the exception of F2902 pin 1 which also has 20v on it, so not blown. Can anyone help me troubleshoot further ? Thanks.

 

[Admin]

Hi all,
Came across this post during troubleshooting of my own T550, which has also just lost it's backlight. The values from above all check out with the exception of F2902 pin 1 which also has 20v on it, so not blown. Can anyone help me troubleshoot further ? Thanks.

first you need to upgrade your account and we are not a hardware repair service you have to check that by your self but we can land you some help .

 

[redart]

first you need to upgrade your account and we are not a hardware repair service you have to check that by your self but we can land you some help .

Wasn't looking for a repair service just some friendly advice, which on most forums is free. Will look elsewhere.