diagnosing no backlight for the LCD

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citivolus · #1 Post by **citivolus** » Thu Apr 05, 2007 1:25 pm

My daughter dropped my X31 when the unit was off. When I power it up, the backlight seems to no longer work. The display is obviously very dim but does work. All other aspects of the laptop seem to work fine. Never had a problem with the LCD before.

I took it apart and physically inspected the inverter, but there were no indications of burn marks. there is also no buzzing sound when it is powered on.

I imagine it's either:

inverter board
CCFL
or the LCD cable

any suggestions on how I can narrow it down before buying replacement parts and swapping them out? I know the symptom indicates the inverter board but I wouldn't have imagined that a drop would cause the components to fail. Rather, if a CCFL is like a fluorescent bulb, I would think that is more likely to fail from being dropped. what do you think?

thanks.

kai · #2 Post by **kai** » Thu Apr 05, 2007 2:55 pm

In this situation, I would attempt to reset the LCD cable. If that doesn't fix it, I'd then buy a new CCFL since they don't actually cost that much, certainly much cheaper than an inverter.

mitchellst · #3 Post by **mitchellst** » Thu Apr 05, 2007 3:08 pm

I've also seen motherboards cause this. If you hook it up to an external monitor and the video is OK, then it's either your LCD or the FL inverter.

If you're interested in having it repaired, PM me for a quote... It sounds like you're planning on doing it yourself, but I had to throw it out there.

citivolus · #4 Post by **citivolus** » Thu Apr 05, 2007 3:09 pm

thanks for the suggestion. i did reseat the lcd cable but it didn't help. the price for the CCFL is about the same as the inverter but from what I've read it is a nightmare to change. i'll need to buy a new soldering iron as well. was hoping for any test that might rule out one or the other parts...unfortunately i only have a T23 and a T40 with which to test parts, and i'm assuming neither inverter boards are compatible since the X31, T23, and T40 all have different screen sizes.

JHEM · #5 Post by **JHEM** » Thu Apr 05, 2007 3:11 pm

mitchellst wrote:correct me if I'm wrong, but the CCFL is the inverter, isn't it?

The backlight or Cold Cathode Fluorescent Lamp.

James

mitchellst · #6 Post by **mitchellst** » Thu Apr 05, 2007 3:13 pm

yes... I quickly realized I needed to be corrected...

I've never actually heard of anyone replacing that part... since the LCD comes with it already attached.

The Spirit of X21 · #7 Post by **The Spirit of X21** » Thu Apr 05, 2007 7:51 pm

Replacing the CCFL is more common than you think. That said, it does take a certain amount of courage to try it. There is a thread and how-to in the 600 section:

http://forum.thinkpads.com/viewtopic.php?t=3705

citivolus · #8 Post by **citivolus** » Mon Apr 16, 2007 10:44 am

well, I took the LCD panel apart, and noticed that the CCFL was completely shattered. however, I'm not certain that I didn't break it while removing the silver reflecter/channel that holds the CCFL. this makes me a little suspect that the sole problem was caused by a burnt out CCFL.

I removed the 2 wire connectors from the end of the CCFL. I could buy a new CCFL from LCDParts and attempt the repair. However, I'm turned off by:

1) my relatively poor soldering skills
2) their high shipping costs ($10 for a paper tube weighing next to nothing)

Anyway, if I could buy an entire LCD panel for relatively cheap, I would consider that. Checking specs, would I be able to use the LCD panel from an X22 laptop for my X31? I see they both have 12.1" screens and XGA resolution.

kai · #9 Post by **kai** » Mon Apr 16, 2007 6:47 pm

Well you've got this far now, what have you got to lose?

There's absolutely no way that you are going to be able to buy an intact LCD screen for cheaper than buying a new CCFL tube.

Good luck.

citivolus · #10 Post by **citivolus** » Fri Apr 27, 2007 12:56 am

well, after many hours, I successfully replaced the broken CCFL and my wife is very happy!

the only problem is that the light seems a bit uneven, but that may be because I had to bend the aluminum channel it sits in to maneuver it in.

I had so many small challenges: the leads which I had to solder were incredibly small, there was no slack in the wire to work with, then the rubber boots split apart so I had to improvise using liquid electrical tape, then the CCFL wouldn't quite fit, then I finally got in in and started putting the laptop back together again only to realize I had put the CCFL into the channel backwards, so I had to start all over again. then one soldered end came apart, etc...

in the end it all works, so I'm thrilled. thanks so much for this forum and everyone's help!

gromek · #11 Post by **gromek** » Thu May 03, 2007 2:13 pm

I bought x30 on auction about two months ago. When I opened a pack I was lost for words because computer has a huge cracked corner. Even hard cover doesn't pass that hit. Contact with seller was really bad and I need a computer immediately. I turned it on and laptop works really fine. It was only one problem that crack didn't allow to close the cover. So I disassemble computer and glued it. After assemblage everything works _almost_ fine. This almost means that is no backlight.
I connected other ccfl to the inverter and that had no effect. So I blame inverter and buy new on ebay. Few days ago I got it and swap with older but it also had no effect. I borrow multimeter and measure the voltage on the out of inverter its equal zero. I don't belive that new inverter is broken.
I don't know what to do now, where is a problem? How check current going to the inverter, all lights in it works, it looks like only a module inverting current to ccfl doesn't work. How check is ccfl works without dissasemble lcd?

Thanks

citivolus · #12 Post by **citivolus** » Mon Jan 21, 2008 12:45 pm

citivolus wrote:well, after many hours, I successfully replaced the broken CCFL and my wife is very happy!

in the end it all works, so I'm thrilled. thanks so much for this forum and everyone's help!

well, unfortunately it's not working again.

I do see the image on the LCD screen but no backlight. The laptop works fine when connected to a monitor.

this time I took the laptop apart and noticed that the CCFL bulb does turn on when I power up the laptop but immediately turns off again. could this be caused by a bad inverter? what should I do to test this?

thanks!

citivolus · #13 Post by **citivolus** » Mon Jan 21, 2008 1:07 pm

this gets more interesting...

i fiddle with the lid hinge switch and the CCFL flickers! i guess this probably means the inverter is ok and my problem is with the lid hinge switch. can this be replaced? time to do more searching!

citivolus · #14 Post by **citivolus** » Mon Jan 21, 2008 2:13 pm

well, I think I got ahead of myself. pushing down the lid switch then releasing simply repeats the behavior of the CCFL when first turning on the laptop. the CCFL comes on then immediately shuts off.

i guess the switch is operating correctly and maybe the inverter is bad after all. i've searched and found the thread on testing the inverter:

http://forum.thinkpads.com/viewtopic.php?t=48910

is there anything else it could be besides a bad inverter? would a bad inverter behave like this (CCFL on for a flash then off)?

diagnosing no backlight for the LCD

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