Author Topic: My HP48G+ has developed a fault (display)  (Read 4525 times)

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Offline SiliconWizardTopic starter

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My HP48G+ has developed a fault (display)
« on: January 24, 2024, 07:09:50 am »
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?
 

Offline WattsThat

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Re: My HP48G+ has developed a fault (display)
« Reply #1 on: January 24, 2024, 12:32:48 pm »
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.
 
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Offline SiliconWizardTopic starter

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Re: My HP48G+ has developed a fault (display)
« Reply #2 on: January 26, 2024, 08:07:27 am »
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.
 
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Offline Silicium81

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Re: My HP48G+ has developed a fault (display)
« Reply #3 on: January 26, 2024, 08:56:21 am »
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!
Electronic engineer with a passion for mechanics
https://vae-tech.forumactif.org/
 

Online iMo

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Re: My HP48G+ has developed a fault (display)
« Reply #4 on: January 26, 2024, 09:10:17 am »
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..
« Last Edit: January 26, 2024, 09:28:12 am by iMo »
 

Offline SiliconWizardTopic starter

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Re: My HP48G+ has developed a fault (display)
« Reply #5 on: January 26, 2024, 09:18:51 pm »
I've seen reports of the same issue with the blue LCD. I don't know if they are more or less prone to this. But yes, the black LCD was the latest, and "best" one. And it can be found in the HP39 and HP49G and a couple others apparently. But if disassembling the latter is as fun as for a HP48, that'll be double the fun. :-DD

The case had already some wear in the bottom corners, so ideally, finding a HP48G(/+/X) in good cosmetic condition, with a working LCD (or at least that would be likely to, without black spots on it), but a non-working board, and cheap, would be the better option. But this looks hard to find.

I'll post a picture of the back of the LCD module - it has a black plastic rectangle that appears welded onto the back of the module. Replacing just the polarizer, which is relatively straightforward on some other LCD modules, looks nearly impossible (without destroying everything.)
 

Offline SiliconWizardTopic starter

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Re: My HP48G+ has developed a fault (display)
« Reply #6 on: January 27, 2024, 03:39:28 am »
Some pics.
 

Offline SiliconWizardTopic starter

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Re: My HP48G+ has developed a fault (display)
« Reply #7 on: January 31, 2024, 11:19:56 pm »
Would anyone know what this black plastic cover on the back of the LCD is for?
I think it's right over the polarizer which should be the white film underneath. If it's that, I would guess that maybe it would precisely help the polarizer stay in place for a longer time than without. If so, that didn't work so well.

Haven't had time to disassemble the LCD yet, I'm expecting it to be painful (no clue how to remove this black cover without destroying everything). Curious to see the polarizer though.
 

Offline helius

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Re: My HP48G+ has developed a fault (display)
« Reply #8 on: February 04, 2024, 07:52:08 pm »
"Tunnel vision" is a syndrome affecting old LCD panels usually caused by polarizer delamination, but it can also be caused by a bad bias voltage.

The HP48s are very hard to successfully disassemble, although the older ones marked "Singapore" are fitted tighter than the newer "Malaysia" models. In both cases the back is held on with clips and plastic studs.
 

Offline SiliconWizardTopic starter

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Re: My HP48G+ has developed a fault (display)
« Reply #9 on: February 04, 2024, 10:02:57 pm »
I have removed the black plastic backplate, it turns out it was just stuck to the reflective film with double-sided tape. I suppose its role is to prevent said film from warping over time.
I then removed the reflective film. And, bad surprise, it's not the culprit. With this film removed, one can see through the glass sheets, and the issue is right between two glass sheets, so it's impossible to repair.

Not sure I'm going to bother replacing the LCD... the same panel can be found on the 39G and 49G, and these can be found for relatively cheap (compared to the 48G at least), but I've looked at teardowns of these, and while their external aspect is different, their internal construction is very similar. So opening them and taking the LCD panel would be just as annoying as opening the 48G, plus the risk of damaging the LCD panel while trying to remove it. Eek. Doable, but nasty.

Too bad. Not sure I want to waste any more time on this one. The main board is in perfect shape, so maybe I'll just keep that in my collection.
 


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