Fixing LCD rot (groups of black pixels) by slow bake

Continuing the discussion from PSION 8088 laptops - MC line:

I see a calculator forum topic which shows progress over three very long slow bakes:
Cooking My DM15L Fixed The LCD

It did take 3 heating to get it all out.

  1. before heating
  2. 3 hrs at 76 degrees C
  3. 3 hrs at 76 degrees C
  4. 4.5 hrs at 80 degrees C

Note the reverse order of these images:


Interesting! I wonder if that method could also work in old handheld games too, it looks promising. Could the problem be some kind of humidity or fungus that affects the reflection angle or something like that? because it seems the liquid crystal wasn’t affected by the problem.

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My feeling is that it’s a (re)crystallisation problem, whereby some patch of molecules adopts a different orientation, so polarises differently, so shows up as a dark patch. But it’s possible it’s some kind of pinhole leak into a layer where it shouldn’t be. It seems to be started by extended extreme cold.

I have a weatherstation which suffers from this. Ideally, the display alone would be baked, but in this case I’d be baking the whole device. But even 80 degrees doesn’t seem too warm to be damaging to electronics… I’d hope.

Edit: I see @zedstarr posted about the MC400 experiments:

My main hope is that the calculator fix baked for much longer.

Edit: in all cases it seems the splodges are a different colour from the proper dark pixels.

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Curiously one of my old Calculators (Casio fx502p) went ‘dark’ after I left it in my car for some time when the overnight temperatures were well below freezing and I discovered that the display would fix itself for a while if I left it over a radiator… Then eventually I fixed itself forever… This was early 1980s.

Now it seems just fine (other than a crack on the front glass).

Slightly related is a recent memory of issues with the Sharp PC1211 (aka Tandy TRS-80 Pocket Computer) with a lot of them developing dark splodges (I have one like that too) but in this case a few years back some enterprising individual actually designed and got new ones made for it…

I can’t find the original articles, but this like on Tindie tells some of the story: