HP 320LX - very dim screen

Hi all.
This is my first post in the forum.

I wanted to do some old school windows CE programming so I bought this device. I did not realize at the time of purchase, but the screen is defective and I can barely read what is being displayed.

Is there a possible solution for that? Contrast settings didn't do much.



Thank you very much!

My 300 series/MC series are all the same, the screen contrast has deteriorated. The backlight was never particularly good in the first place, but they seem to slowly get worse with time. I am not sure what to suggest aside from doing a LED mod on them which a few people have done.

How does it look without backlight? Still the same?
Could be a problem with the polarizer if it is still washed without the backlight.

The backlight doesn't make it any better or worse. Just a little brighter with the backlight but still very hard to read.

Hm.. hard to tell from the distance but I guess there is something wrong with the polarizing film. It may well be that the LCD slowly blesses the time.
Could you take a picture without backlight? in a bright room

Thanks for helping.
I have recorded a video. It seems like if I get the angle just right, I can see it better.

]
Video 1 - in this one I Even turn backlight on and off.


Video 2 - here is in a different angle. It has more reflex but you can also see the contents a bit better.

And here is a slightly better picture:


When looking on a diagonal, I can see some "air bubbles" which I suppose are the resistive touch but if you look closely, seems like there is some darkening of the screen in the center area, about 1cm margin of the screen.


Very hard to see on this picture.


It is hard to take pictures or record without a big reflection because its soooo dim. The start button is barely, just barely visible.

Edit:
I did some research and I see that more often than not people will replace the gameboy polarizer. Starting to think there this is looking like a good candidate.

Yep could be the polarizer or the screen itself. Loosen films maybe.
Do you use a translate or do you really mean Gameboy?
Could be a possibility to replace the polarizer but you need the same dimension.

Yes, there are dozens of videos on how to remove and replace the polarizer on Gameboy devices. In general they will buy a larger piece of polarizer and then cut it to the size of the LCD. Replacing it does not seem hard, but could be risky in case I damage the display it's probably gone forever.

I have never done this process and never took apart a 320LX. Do you know of any guides on how to disassemble it?
Not sure how to disassemble the lid, it seems to have two screws near the feet, is that all?

There are a couple of some good sites with tutorials of some LX palmtops.
Tear down

Although in your last photos it doesn't look that bad without the backlight. hm...

I would say that it is a bit dimmer than mine. Is it the same on both battery and AC?

If I am on battery and then I plug the AC cord, I see absolutely no difference on the screen.

Edited by wmundstock 2023-01-18 9:21 PM

Same "problem" here with mine. But the brightness of the backlight or the contrast of the display itself was never as good as with actual devices. When the HP200LX came out I was dissapointed with the display contrast compared to the older HP95 (different technology). Many folks kept their HP95 for the better (text only) display.

This was the problem with many new devices with hi-res bw-pixeldisplays during the nineties. The advent of color when the HP620 came up was impressive. These displays were crisp and bright compared to the older ones but the power drain on the batteries was also impressive .

Maybe you could open it and find a resistor that limits the current through the display (or increases the refresh frequency). Sometimes there even is an adjustable resistor.
I revived some displays from the 80ies with that trick that otherwise seemed to have faded.

Stefan

Reminds me of the display on my old CE 2.01 Palm-size PCs. Is the 320LX's display 2-bit grayscale? I'd imagine the limited contrast levels could be a factor.

Ah, yes, the Palm-PC. While writing my text I thought of these rigs but I didn't come up with the name.

As I remember it they were the best example for a weak display right by design. Even the 5 years older DOS-palmtops were better.

And yes, the older HPs have that 2-bit-display, too

Stefan

That is an interesting approach Stefan, thanks for sharing. So, you don’t think its the polarizer?

Have you ever seen the schematics for this main board? That would be a big help. I suppose the resistor would be near the lcd flat cable region in the maimboard. I will look for some adjustable resistor first.

I have some experience with electronics but not enough to reverse engineer a mainboard like this. Any tips are welcome...

Thanks