[Duo2400] Duo 280 darkening screens

[Grizzlygiant]

Tom and Lisa P wrote:
> 
> I hve several Duo 280 screens that go dark in the corners after the
> screens are on for some time.  The last theory I heard about this
> problem was that it was the backlight going out over time.
> 
> To confirm this, I tried an experiment.  I removed the backlight and
> left the duo on for 4 hours one night.  At no time did the backlight
> seem to dim.  This would seem to indicate that a dimming backlight is
> not the sole problem.
> 
> Any other ideas ?
> 
> Mad Dog

Hello Mad Dog:

There was much discussion and experimentation about this on the
PowerBook list about 3-5 months ago.  We haven't found any way to cure
this, to date (except a new screen) and I myself could find no _real_
cure, except to push on the screen where it is darkening dozens of times
and that only works for a few minutes.

Temperature is not the problem as some even put their screens in the
refrigerator and the problem still occurs.  I have taken my screen
(which exhibits this problem) completely apart and could find no
shorting or broken leads or corrosion between the transistor leads.

I believe that this is a result of poor manufacture and that the two
polarizable sheets which form the screen have minimally separated and
are actually leaking a small amount of voltage which causes heat which
causes more separation which causes more leakage, etc.  I'm not certain
about the film separation, but I'm pretty sure about the voltage leak
(where ever it comes from) because the polarizable pixels are both
turned "on" which is what causes the darkening.

Out of the 4 PB500 series active matrix grey scale screens that I have
seen so far, 3 exhibit this problem.  They were all made by (I think)
Holiden (I know the name starts with an H).  The one that is good was
made by Toshiba (and it has 10 dead pixels).  I have not seen this
problem in the 3 passive matrix grey scale screens I have or in the two
active matrix color screens that I have.

I also think that this may be caused by leaving the screens in a hot
environment for too long, which is why Apple suggests not to leave the
PB in a hot car.

Sincerely yours, Grizzlygiant