Duo 280 darkening screens

[Marc Sira]

> 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.

This is a possibility. My theory (which has been alluded to recently) was
that atmospheric pollutants leach into the screen corners (and eventually
edges) and essentially cause doping, which facilitates ion transfer and causes
a charge to build up. The only cure I've found is time spent with the display
unpowered so the charge can dissipate, but physically working the panel as you
describe could probably speed up the process. The effect is related to the
memory effect that's observed when a static image is left on the screen for
a while (which began this latest discussion). That effect is completely normal
btw, and always goes away with time when the image is removed (fastest when
the screen is off). The difference at the screen corners is that the onset
is much faster, and the pixels always become darker regardless of what's
displayed - thus I suspect doping.

One thing I don't like about your theory is that it should cause accelerating
damage, which hasn't been my observation (fortunately).

> 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've never seen it on a colour screen nor a passive screen either, so you may
be correct that it's a manufacturing defect (not that these machines were ever
designed to last this long). I do observe that all Duo colour displays darken
with age and use, but I think this is the backlight wearing out (plus modifed
expectations as newer models get brighter and brighter screens). That was also
mentioned in the initial query about a darkening 280c. Entirely different
phenomenon from the screen corners, of course.

-- 
Marc Sira		|	toh at victoria.tc.ca
If you can't play with words, what good are they?