New theory on the cause of the infamous Tunnel Vision problem - Testers needed!

[3lectr1cPPC]

Great info, thanks.

 

[alexGS]

Usually the polarizer I got didn't have the retarding film, so naturally black/blue on whitish yellow LCDs would acquire a greenish-yellow (think chartreuse) tinge, always with black pixels. Odd color, but much better contrast.

Ahh… I’ve found the same, experimentally. Removing the ruined polariser from, say, a Powerbook 150 passive-matrix screen seems to expose an additional grey layer that is also ruined and has to be scraped away. I was thinking that was the film-compensating layer (of FSTN) but I had seen the name ‘retarder’ somewhere else - I’m glad you mentioned it.

The result of not having the correct polariser is a display with yellow background and dark purple pixels, in my experience.

Could you please help me to find a source for the best type of polariser film to use on these mono LCDs from the early 90s? I’m having to do it by trial-and-error and I haven’t found anything great yet.

Cheers!

 

[GRudolf94]

Did you swap the rear one also? I forget if that helps the yellow and purple - it does happen sometimes. My first 150 attempt looked yellow/orangeish. I've not yet nailed down all the bits of science that go into this. Unfortunately there's a lot of variables to fixing LCDs.

 

[alexGS]

Did you swap the rear one also? I forget if that helps the yellow and purple - it does happen sometimes. My first 150 attempt looked yellow/orangeish. I've not yet nailed down all the bits of science that go into this. Unfortunately there's a lot of variables to fixing LCDs.

Thanks - I don’t think I did the rear film on that one, but I replaced both on a different LCD recently also with yellowish results. I think I just need to find a better source of film.

Meanwhile, we’re off-topic for this thread - sorry about that - I just got excited thinking perhaps someone had found the secret source of DSTN polariser film with retarder

 

[bwinkel67]

I've gotten a few inquiries about how my "100 degree celsius bake to fix tunnel vision" on my PB 180 has held up after a year. It's been about 18 months now and no ill effects or return of the issue. I just had it on for about 4 hours with the screen looking normal. I don't use my PB180 on a regular basis and it was stored on the shelf for the summer. Though no tunnel vision effects appear when the monitor is on, you can still see the remnants of what happened before the fix when the LCD is off. The old tunnel vision area appears subtly lighter, when viewing it at a certain angle in certain lighting, though not when looking at it straight on (basically at its worst state...i.e. mine never went completely dark, just a little over an inch on the sides and an inch and a half on the corners). It's not visible when the LCD is on, i.e. it looks normal.

 

[Paralel]

The panel retaining a bias. LCDs are driven with AC waveforms that get switched around to try and work around this persistence thing (just read any old panel datasheet and there'll usually be a pin doing that.
Mono polarizers look different because of a retardation film, this is just a filter layer.

I have a vinegar'd 180 panel - the one I intend on using for testing my ideas on vignetting (that's currently 8000mi from me) that would like a word about that.

The charge retention is why the moisture invasion from a bad seal for the Hosiden active matrix mono LCD's makes more sense than the competing theory for tunnel vision. The other theory has no mechanism to explain how the charge retention occurs. For the moisture invasion theory it is easily explained that the moisture can create a parasitic capacitance which temporarily provides enough energy for image retention. Eventually the parasitic capacitance loses its stored charge and that is when the retained image is lost. That's why it isn't a true "burn in", it's a pseudo "burn-in" because the retained image will dissipate if disconnected from any power source for several days. I have been able to demonstrate this when a Hosiden LCD from a Powerbook 540 was completely stripped all the way to the down to all its various individual pieces of polarizers and diffusers along with the glass sandwich that contains the liquid crystals and TFT. I was able to show the retained image in the tunnel vision region by replacing the polarizer on the glass sandwich, showing that the retained image is inside the glass sandwich when it is attached to nothing, indicating that it is within the liquid crystal layer itself. The only way that would be possible is if the source of the power for the liquid crystals was within the glass sandwich. Parasitic capacitance in the liquid crystal layer makes the most sense for how this is possible. The best answer for parasitic capacitance in the liquid crystal layer is moisture intrusion.

Anyone can test this for themselves. Take a Hosiden active matrix mono LCD that hasn't been baked and has a retained image after being powered down, strip it down completely to all the individual components of the screen. Put the polarizer back over the glass sandwich that isn't attached to anything and you will see the retained image. Give it a few days at the most, and you will see when placing the polarizer over the glass sandwich now that the retained image is lost, because the parasitic capacitance has dissipated. The competing non-moisture intrusion theory for tunnel vision can't explain this behavior with their model of how tunnel vision occurs.

As far as baking a screen in a vacuum, as far as I know, no one has been able to do this due to a lack of proper equipment.

 

[3lectr1cPPC]

It is also now worth noting that Color LCDs made by Hosiden can also be affected by tunnel vision. @techknight ran into this in multiple panels from the IBM ThinkPad 750C, which uses an active matrix color display from Hosiden.

 

[Paralel]

It is also now worth noting that Color LCDs made by Hosiden can also be affected by tunnel vision. @techknight ran into this in multiple panels from the IBM ThinkPad 750C, which uses an active matrix color display from Hosiden.

I guess this proves that Hosiden's methodology of creating LCD's at that time was just crap.

 

[GRudolf94]

Hosiden goes on the same sh*t list as Reflektor Saratov for me, now. Soviet Reflektor LCDs are apparently sealed together with shellac, which doesn't bode well for their durability.

 

[techknight]

Yep... See here:

 

[naujoks]

Yeah really crap QC, blasted things didn't even last 20 years!