Z88 LCD panel

Discussion forums for users of the Cambridge Z88 Portable Computer
bwinkel67
Posts: 146
Joined: Mon Mar 23, 2020 2:38 am

Z88 LCD panel

Post by bwinkel67 »

Not much Z88 content on here. I did a general search and nothing came up. Maybe I'll be the first person to post. In any case, I've had mine since about late '89 I think (or early '90). [Edit: I was looking in the wrong place and the sys admins moved my post to the appropriate area.]

When I took it out of mothballs last year I noticed a column of pixels wouldn't turn on so I recently decided to take it apart. I figured I would take the bezel off and the LCD panel would be connected by two electromeric strips. Alas, the Japanese panel manufacture for Clive's laptop had a paper thin ribbon on the end for the rows, glued on top of the panel. That was fine, except, being paper thin, it creased upon opening because there was backing tape to the ribbon to secure it to the LCD, which was stiffer than the ribbon. Once creased you could see that the traces had broken. Just the worst designed LCD panel I have ever seen. I've taken the LCD apart for my other retro computers, a PowerBook 180 and a TRS-80 Pocket Computer, and both were pretty easy to work with.

So I tried to fix it by first cutting away the 1 centimeter creased item. Then I had to figure out how to expose the traces and I played with the cut away item and a swiss army knife; gently scraping along the traces SOMETIMES worked. Since I had so little ribbon to work with, I figured it was pretty much a lost cause. Well, after my first try and accidentally scraping away some traces, the second try I just went with less and got it to work. All back together. I used a pressure fit with some rubbery material to have the bezel press down to make good contact (as I said, they somehow glued it on which took a while to clean off). Oh, and the best part...the dead column of pixels is still their as it must be an issue inside the LCD panel. As Homer Simpson would say...D'oh.

Has anyone else had any experience with the Z88? I'm curious if the screen, made by OPTREX in Japan (model DMF690N), was used by other machines since I'd still like to see if I could find a replacement to fix the bad pixels

Z88-fix.png
Jbizzel
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Joined: Thu Apr 23, 2020 6:58 pm

Re: Z88 LCD panel

Post by Jbizzel »

Have you seen this...

https://hackaday.com/2019/03/03/designi ... computers/

Would something similar be possible for the z88?
bwinkel67
Posts: 146
Joined: Mon Mar 23, 2020 2:38 am

Re: Z88 LCD panel

Post by bwinkel67 »

Most definitely. Robert had to spend a lot of time reverse engineering the LCD panel to work with the TRS-80 Pocket Computer 1. I was one of his first customers and replaced my LCD a couple of years back. Works beautifully. With the Z88, it should be simpler since it's just square pixels at 64x640. It does have different levels of intensity since you can have bold and light text.
Jbizzel
Posts: 64
Joined: Thu Apr 23, 2020 6:58 pm

Re: Z88 LCD panel

Post by Jbizzel »

Brilliant! I love that project. Those machines seem rare as hen's teeth!!!

I think there are quite a few z88s with damaged or completely broken screens.

It would be an interesting project for sure.
bwinkel67
Posts: 146
Joined: Mon Mar 23, 2020 2:38 am

Re: Z88 LCD panel

Post by bwinkel67 »

Jbizzel wrote: Tue Feb 14, 2023 8:49 pm I think there are quite a few z88s with damaged or completely broken screens.
Really? I figured, other than having an idiot (like me) open it up for no good reason, it's hard to see how they would fail. Are you talking about physical damage from dropping, stepping on, etc...
Jbizzel
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Joined: Thu Apr 23, 2020 6:58 pm

Re: Z88 LCD panel

Post by Jbizzel »

bwinkel67 wrote: Wed Feb 15, 2023 8:45 am
Jbizzel wrote: Tue Feb 14, 2023 8:49 pm I think there are quite a few z88s with damaged or completely broken screens.
Really? I figured, other than having an idiot (like me) open it up for no good reason, it's hard to see how they would fail. Are you talking about physical damage from dropping, stepping on, etc...
Well, I did a survey recently. I've had 20 responses so far, and 5 mention possible screen defects. I have 2 Z88, both were bought with screen issues, although I managed to get a new from old stock screen for one - a long time ago.

According the the EPROM Usergroup mags, the screens can get damaged from being too hot, too cold, or by being exposed to direct sun light for long periods.
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1024MAK
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Re: Z88 LCD panel

Post by 1024MAK »

LCD screens can also be damaged by stress (physical) and vibration.

As well as absolute temperature extremes, a relatively large change in temperature within their normal range can also affect them, such as bringing in from a cold area to a much hotter room or the other way round.

They can also develop defects while stored even if not used.

There are numerous failure modes. As all complex displays are multiplexed, failure of any of the control/data or matrix of lines will cause rows or columns to either stay in the “off” (background) colour or stay in the ‘on” (foreground) colour.

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bwinkel67
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Re: Z88 LCD panel

Post by bwinkel67 »

My fix was almost perfect, except for one weird behavior. At full contrast, all pixels (except for the bad column that is likely within the LCD) turn on fully and look perfect. At normal contrast all is well too. But at half contrast, rows 3-5 are lighter. This also shows up at normal contrast when I bring the Calculator app to the foreground. This dims the rest of the stuff on the screen and you can again see a bit of lighter streaking in rows 3-5. It's weird since at full contrast it's perfect.

I'm guessing that those 3 contacts on the ribbon either had a bit of plastic left (I tried not being too precise scraping it off since I had so little to work with), or it's just slightly misaligned to the contacts on the LCD since scraping also stretched the front end of the ribbon slightly. The electromeric strip for the columns is perfectly aligned, because I had to open things up again after my initial fix, and align it more to the right. When it was misaligned, it caused the M in PipeDream and the D in PrinterEd (both the last letter in the menu window) to have missing pixels in their first column. I can definitely live with that, considering how SOL I felt after having kinked the cable and broken the traces. :(
bwinkel67
Posts: 146
Joined: Mon Mar 23, 2020 2:38 am

Re: Z88 LCD panel

Post by bwinkel67 »

So I bought a broken spare Z88. The owner said he put batteries in and it started to smoke. It sure smells like it. This seems to be a US version (like my QL it had internal metallic paint).

It also has a trap door next to the Z80 where the expansion bus lives (anyone every create ayn add-ons?). Finally, the LCD panel is not made by OPTREX, but instead by EPSON (EG2001S-AS-1 8806A3). It's also constructed differently as it has it's panel completely enclosed in plastic with screws on the top.

You can barely see my old panel but that has a metal bezel pinched to the green circuit board. This one has plastic bezel on top and bottom, screwed together (actually a bit lighter). This may not have a ribbon cable to the side since there is less room...though maybe it just folds underneath it (I'm not about to open it up and push my luck). Since I fixed mine, the only reason I'm swapping is because I still have the column of bad pixels, likely due to a flaw in the LCD panel.
IMG_2625.JPG
Jbizzel
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Joined: Thu Apr 23, 2020 6:58 pm

Re: Z88 LCD panel

Post by Jbizzel »

Great thread! I have 2 z88's one with each screen type.

However, the screen with the plastic bezel is in bad shape, with weird squiggly lines of dead pixels running through it at the corners.

From reading the EPROM User Group documents, I note that there was a lot of concern about the screen being damaged by direct sun and hot and cold temperatures. I wonder if that's what happened to mine.

However, thanks to you I remembered that I had a spare screen lying around. I removed it in the past because it had a blemish in the middle of the screen. After reading your thread I decided it might still be better than the screen I currently have installed and I switched them.

Here is the crazy thing - the screen no longer has the blemish! It seems to have 'healed'. How is this possible!
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