The dreaded bleed!
The bane of so many glorious early Casios, particularly those with duplex screens, along with numerous other early digitals from other brands, this failure is a result of the edge sealing giving out, and air entering the liquid crystal envelope between the glass plies. The front and rear polarisers on positive-display screens (those with black figures on a light background) are oriented at 90° to each other, and without the intervening fluid in place they block the light.
If only minimal bleed is present, sometimes it’s possible to improve the situation by removing the LCD and carefully squeezing it to manipulate the air bubble/s into a less intrusive position, with luck all but hiding the bleed. This is quite difficult, but using a slightly domed watch glass to apply the pressure makes it far easier because then you can see what’s happening as you’re applying the pressure, rather than continually checking afterwards. This is, of course, a dirty hack, and the possibility exists that it may worsen the leak/s… but at present no other option exists, short of sourcing a replacement.
If the liquid crystal fluid was readily obtainable (it’s horrifically expensive, and there are a number of varieties, while it’s not clear what the original fluid is and/or how compatible anything currently available is), employing a vacuum pump to replace the air with fluid might be halfway practical, but that still leaves the extremely tricky problem of re-sealing the display, something extra problematic in the vicinity of the zebra strip contacts. If it’s even possible, it may be more trouble than reverse-engineering the displays and having them remanufactured, once twenty or so have been repaired… Oh, and that fluid is probably rather carcinogenic, by the way.
Bastard rainbow, AKA LCD burn
This one is another show-stopper; the above still is taken from a VDW vid in which a barely visible rainbow pattern is made overwhelmingly obvious by an attempted fix – fresh polarisers actually make this problem worse, because the concentric rings are mysteriously caused by the fluid generating varying angles of polarisation. In extreme cases, a medium-dark blue spot will be made black by new polarisers, and this is a region where the display is actually negative; any activated segments within the spot show up light on dark. Confusingly, this doesn’t seem to be the case with original tired polarisers, but perhaps it’s merely a matter of degree.
In any case, be warned – if contemplating polariser replacement, look hard for faint rainbow rings. The segments will need to be quite faint indeed to be worth making the rainbow pop. I have tried to tackle this phenomenon by physically harrassing the glass envelope with increasing vigour, up to a worrying degree of violence, in an effort to stir and mix the fluid, to no avail whatsoever.
Faded elements / brown screen
Now for some good news – the above syndrome can be repaired, although at some risk; sadly this particular display suffered significant bleeding during polariser removal and was ruined. However this is the only such failure out of a dozen or more polariser replacements performed to date, so those aren’t terrible odds… Furthermore, in the cohort of watches likely to suffer from failing polarisers (up to mid 80s at this point), the adhesive securing the polarising layers (usually the front one) may have begun discolouring, lending the screen anywhere from a sepia tint to a full-on poo brown colour in the worst cases, and of course replacing the polariser also replaces the adhesive.
Removing the adhesive is perhaps the most difficult aspect, after trying to be gentle enough not to create a bleed; the adhesive seems relatively unaffected by solvents, and the best method discovered so far is simply slicing as much of it as possible from the surface with a razor blade. Removing the remaining residue seems to go best by merely rubbing it off by thumb. It’s best to try and get the polarising film off in one piece, so it can then serve as a template, to simply stick onto the replacement film to cut around.
To choose the orientation of the film, it’s been found necessary on some varieties to peel a small section of the adhesive backing away, as it can interfere mightily with the polarisation effect. Having determined the best orientation, the next difficulty is cutting out the section of film, as it can be tough to get a nice cut so some practice may be required. Lastly, the cut edge is likely to have a slight lip caused by the shearing of the scissors (good luck simply cutting through it with a single blade), and this raised edge can play merry hell with adhesion, so it’s definitely best to cut the film with the adhesive side up (marking the protective film with a symbol which looks different when mirrored is advisable).
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