Lenovo X201 "no backlight" trouble

[derick]

Hello, I bought X201, with backlight issue. I have idea replace fuse F1 for normal working order. But fuse F1 was OK (not blown). I measure some voltages behind the fuse and around 19 volts was present, even on led section of LCD panel. But there was no backlight and still no change. I have also X200s with CCFL lcd assembly, so I tried install (LCD+cable+led board) from x201 to it and it works normally. (nice and strong backlight).
I read some forums about any unknown X201 motherboard backlight issue. Anyway, I connect CCFL assembly from my X200s to X201 board and it normally works!!! (normal backlight) So question is, why only CCFL assembly is working with my X201 mainboard and LED not, where can be a problem?

[nitrocaster]

Can you see an image on the screen when using LED assembly?

[derick]

Yes, thinkpad logo is visble, but very dark, without backlight.

[RealBlackStuff]

There is a MOSFET FDC655BN-GP 6-legged chip nearby, with motherboard P/N Q49.
Marking on chip possibly "55B"
This apparently is not always working properly and may not be needed for CCFL (only guessing here...)
(Found on page 24 of the X201 schematics).

[derick]

Thanks for info, I have couple of dead boards Acer, Lenovo,HP etc and I will looking for 55B mosfet. But x200s seems to be a better choice for portable work, than x201. (weight and battery life)

[ajkula66]

where can be a problem?

The problem may very well be in the LCD assembly itself.

The fact that the board works with the CCFL panel but not with the LED one is where my train of thoughts comes from.