Strange LCD back light failure

[Andy Cuffe]

I have been repairing a number of older IBM laptops recently and I've
encountered a very unusual problem with one on them that I thought
would be interesting to share.

The symptoms were a good picture on the LCD, but only red was visible.
Brightness and contrast were normal considering that only one color
was working. I expected to find either a bad video cable, or bad LCD
driver. What I actually found was that the CCF tube was emitting RED
light. It's bright, evenly lit and doesn't flicker. The phosphor
coating is white and looks like any other CCF tube until you turn it
on. It's a nice bright shade of red and really looks like it was made
that way.

I replaced the tube with one from a similar broken display, but I'm
still curious about how this could have happened. My first thought
was a gas leak, but I thought the phosphor determined the color. This
tube has been stable over at least the 6 months since I first tested
the computer. I took a picture which I can e-mail to anyone who want
to see for yourself.
Andy Cuffe
baltimora@psu.edu

 

[Mike]

its a common failure of the tubes.

the IBM600 was notorious for that.

it would light red, and then eventually it would clear up to white.

sometimes not, and the ccfl will shut down.






"Andy Cuffe" <baltimora@psu.edu> wrote in message
news:qlgk40d4lvnkltqlb2pugd77hseh8pcirq@4ax.com...

I have been repairing a number of older IBM laptops recently and I've
encountered a very unusual problem with one on them that I thought
would be interesting to share.

The symptoms were a good picture on the LCD, but only red was visible.
Brightness and contrast were normal considering that only one color
was working. I expected to find either a bad video cable, or bad LCD
driver. What I actually found was that the CCF tube was emitting RED
light. It's bright, evenly lit and doesn't flicker. The phosphor
coating is white and looks like any other CCF tube until you turn it
on. It's a nice bright shade of red and really looks like it was made
that way.

I replaced the tube with one from a similar broken display, but I'm
still curious about how this could have happened. My first thought
was a gas leak, but I thought the phosphor determined the color. This
tube has been stable over at least the 6 months since I first tested
the computer. I took a picture which I can e-mail to anyone who want
to see for yourself.
Andy Cuffe
baltimora@psu.edu