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My HP48G+ has developed a fault (display)

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SiliconWizard:
Yep, this is my HP48G+, the display has developed a fault relatively recently, sort of all of a sudden (although as I don't use it often, it may have developed over a few weeks, but no more than this.)

As you can see, there is a large black circular halo in the center of the display, visible both when off and on. At first, I was afraid it would be some leak of liquid crystals, but as one can see on the picture, when on, the black area shows the pixels in reverse. It looks to me as though it's "just" the reflective film on the back of the LCD display that has detached around the center. Apparently, this is not something uncommon with old LCD displays.

What do you guys think?

I don't use it much anymore, but keep it as a collectible, and it was in pretty good condition until recently (apart from some wear on the case). So that's a bit sad.
Opening this bad boy is not too much fun, it requires drilling into plastic rivets.
I don't know if we can find replacement displays - apart from getting ahold of another HP48 with a working display and scavenging it. But these tend to be expensive these days, even when not in great shape.
If it's the reflective film, do you think trying to replace it makes sense, and where do you think I can find this kind of film?

WattsThat:
Yes that is a bad polarizer. Finding one of the cheap, first generation 39G’s is the easiest way to source a replacement lcd. Yes, they are a pain to replace but you don’t need to drill out the rivets, those units can be popped apart quite easily.

SiliconWizard:
Popped apart quite easily... not really. I opened it and it was a bit of a nightmare. That's seconded by most people who have actually done it. HP wasn't so good with the right to repair already back then. Horrific construction.
I chose a method that didn't require drilling, but I kind of regret it. Drilling would have been much cleaner in the end. The method I used makes the metal plate bend quite a bit, making it tough to get it back to shape properly for the keyboard to operate well. It also made some rivets pop that weren't supposed to (some that held the keyboard parts together). The construction is extremely finicky. No clue why they came up with something that terrible. It also makes it prone to failure eventually, even when not trying to open it, as the keyboard is connected to the main PCB with some flat cable just by pressure. In comparison, opening most modern mobile phones is a picnic. :-DD
It couldn't have been made to even be serviceable by HP themselves. Either they thought their products were too good to need any repair, or they would just replace them with a new item in case one failed before the warranty period would be over. Puzzled.

And then, once open, removing the LCD display looks like something else as well. The fun has just begun. I'll post some pictures when I get around to it.
For now, I tried heating the back of the display with hot air to see if I could glue the polarizer back this way, but no luck. It made only a minor difference. Looks like a bubble formed in the center. I don't know where it comes from. I've heard that this happened mainly in very humid environments - over here, it's very dry.

Silicium81:
This reminds me of my youth, I modified HP48s by adding 128 or 256k of memory.  8)
I made a template to drill 6 or 8 holes from the back. The opening was thus easy and clean.
Good luck with the screen, my HP48G 256k is not affected yet!

iMo:
My HP-48GX got a single pixel ON even without batteries inside. After I put batteries inside and let running it for a week the issue disappeared (that was 15y back). Since then I've been powering it on for a week every 5 years and none issue so far  :D ..
Opening the case is almost lethal, imho, there are videos with some "successful" attempts, but adding a memory via the cards would be a better option, imho.
Btw. my PC1251 suffered recently from the black LCD too (looking at it every 5-10 years, purchased in 1982/83)  :(, that is a known issue as Sharp Co. used to use a low quality glue in their PC-12xx series and the moisture went inside the LCD..

PS: your display is black - that was "the latest and the best contrast LCD every user wanted to get" with the HP48 series, afaik.. I wonder whether it might be caused by the lower quality of their latest LCD variant, or the "blue" LCDs are affected as well..

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