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Paper Tape
Posts: 3
Registered: ‎12-25-2011
Location: USA
Message 1 of 6 (1,214 Views)

T400 screen very very dim

Screen is almost dark, I can barely see anthing.   External monitor works fine.

 

I searched previous post and found out 3 possibilities:  inverter, backlight, or motherboard.

 

However, one additional thing is that all icons (power, battery, harddisk, etc) underneath the screen are not illuminated, except the very left one (should be wireless).

 

Can somebody kindly help me to diagnose that which part cause this issue, inverter, backlight, or motherboard?

 

Thank you in advance!

 

 

Community Moderator
Posts: 3,933
Registered: ‎01-01-2010
Location: San Francisco
Message 2 of 6 (1,199 Views)

Re: T400 screen very very dim

Those symptoms usually mean 2 fuses are blown on the motherboard. (maybe only 1) If I were diagnosing, I would try a 2nd LCD before playing with the motherboard. Fuses don't usually blow for "no reason". Was something else going on? Do you know whether you have a CCFL or LED backlight? If nothing else was going on, and you have a CCFL backlight, and the fuses are blown, I wouldn't do anything to the motherboard without swapping the inverter. Unfortunately, most repair guys do not/cannot change fuses.
Guru
Posts: 9,240
Registered: ‎12-26-2009
Location: Toronto, Canada
Message 3 of 6 (1,197 Views)

Re: T400 screen very very dim

It could be any of the three, or the cable itself.
W520: 2720QM, Q2000M at 1082/1376, 32GB RAM, 500GB + 750GB HDD, FHD screen & MB168B+
X61T: L7500, 4GB RAM, 500GB HDD, XGA screen, Ultrabase
W550s: 5600U, K620M at 1164/1281, 16GB RAM, 512GB SSD, 3K touchscreen
X200s: SL9400, 6GB RAM, 160GB HDD, WXGA+ screen
TPT1: 1839-23U
Paper Tape
Posts: 3
Registered: ‎12-25-2011
Location: USA
Message 4 of 6 (1,189 Views)

Re: T400 screen very very dim

[ Edited ]

Thank you, Richk.

 

It is CCFL, and yes it blew when the laptop got "not responding" on accessing external hard drive (and I couldn't kill that process).

 

But how to tell if the fuses are blown or not after I unscrew the monitor?  You mean I will need a new motherboard If the fuses are blown (because fuses are not replaceable)? 

 

Community Moderator
Posts: 3,933
Registered: ‎01-01-2010
Location: San Francisco
Message 5 of 6 (1,167 Views)

Re: T400 screen very very dim

Those activities should not affect the fuses or the inverter. Is it still under warranty? If it is, now is the time to call. There is no way to tell if the fuses are blown without complete disassembly. You need to put a meter across the fuses to see if they are blown. (open circuit) Lenovo will not change the fuses. You would need someone who does board-level repair and can get the parts. (often, organ donors) It is a multi-level board with lead-free solder that melts at a VERY high temperature, so you need fairly good equipment. (not a job for a radio shack soldering iron)
Paper Tape
Posts: 3
Registered: ‎12-25-2011
Location: USA
Message 6 of 6 (1,142 Views)

Re: T400 screen very very dim

Thanks richk. I think I'll just use an external monitor which is the simplest way for me...

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