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Tunnel Vision On Monochrome Active Matrix Powerbooks

Paralel

Well-known member
I was wondering this as well. What if as the screen heats up from the backlight or something like that, the polarizing film is pulling away from the screen, or it's properties are being altered slightly.

 

Paralel

Well-known member
Well, I have another 540 on the way, so we have another potential victim... I mean screen... to test with. I will be much more careful with this one.

First test here will be to hand it off to UniServer to test with the vaccuum + rice. If that fails, baking, very low temp will be next.

In the name of science and vintage mac preservation!

 

uniserver

Well-known member
hand it off to UniServer
lol - it was just my idea,I do not have a any of what is needed laying around.

I suggest oven it for 190 for 2 hours, test.

OR if you want to purchase the supplies mentioned, Rice/Bucket/V-Pump/tube/fittings maybe you can be the certified tunnel vision screen fixer man. ?

 

Paralel

Well-known member
Ah, I thought you had the stuff.

Yeah, if this next one has it I'll have to look into what I can do.

 

Bunsen

Admin-Witchfinder-General
A vacuum cleaner would do as a budget vacuum pump, if you can jury-rig something to seal the bucket once (partially) evacuated. Like a tennis-ball stop valve, or a simple faucet.

Refrigerator compression pumps work well, I hear.

 

techknight

Well-known member
you gotta pump it down to at least, 30 maybe? I cant rememeber the scale but thats what it is for HVAC to boil water off... The stronger the vacuum, the more it pulls down the boiling point of water.

 

techknight

Well-known member
Anyone have a make and model of the LCD screens affected?

I have noticed PB180s that had tunnel visions, and ones that do not. For example, mine does not. But I noticed a difference in picture between the two. Like 2 different manufacturers.

Something to check...

 

Mk.558

Well-known member
*looks at his Duo 230 passive matrix display and grins smugly*

Would cold temperature application help as well? I don't know how many specimens we have available but it would be interesting.

It could also be interesting to inspect color active matrix TFTs if they run extended intervals of greyscale or black & white.

 

techknight

Well-known member
I havent seen liquid crystal fail in color LCDs except the new shit. Ive seen plenty of those fail due to layer seperation or contamination. (but thats normal with new shit).

However only other thing to worry about is buffer drive IC failure in the LCD displays. (causes lines/stripes, and dead patches).

 

James1095

Well-known member
Vacuum cleaners move a lot of air volume, but they are about the worst thing you could find for pulling an actual vacuum, probably less effective than sucking the air out through a straw with your mouth.

A refrigerator compressor actually makes a pretty decent vacuum pump. The best I've found are the rotary compressors commonly used in window AC units. Those are about as good as you can get without springing for a real vacuum pump.

Refrigeration service pumps are two-stage vacuum pumps that will go down to a few microns in theory, although the rubber charging hoses and fittings are typically pretty leaky under vacuum. High vacuums are notoriously difficult, very *very* small leaks can spoil the fun and materials that normally seal end up being quite porous. Even stuff that doesn't leak may outgas for days and require steady pumping.

The biggest problem you will have trying to deal with any sort of decent vacuum is finding a suitable chamber to contain it. Pump down to anything resembling a vacuum and you end up with >14 lbs pushing in on every square inch of the chamber, and from this standpoint, the difference between a hand pump for bleeding brakes, testing automotive vac servos and such, and a fancy high vacuum rig with a diffusion or turbomolecular pump is actually very little. Think of how thick and heavy the glass of a CRT is and how violent the implosion can be if it breaks. That is the sort of forces you will be dealing with and most containers you'll find around will simply collapse.

That said, you may not need much of a vacuum to draw the moisture out if you are patient. I have done a bit of potting and casting in epoxy resin and used a plastic bucket with a hand pump to draw just enough vacuum to draw the resin into the nooks & crannies and draw out the air bubbles. Pumping it down to just the point where the sides of the bucket were starting to bulge in was adequate for that task.

 

Gorgonops

Moderator
Staff member
Vacuum cleaners move a lot of air volume, but they are about the worst thing you could find for pulling an actual vacuum, probably less effective than sucking the air out through a straw with your mouth.
A while back I saw a web page that explained the physics of it and can't find it so now but... yeah, it's actually impossible for a direct single-stage fan (which is what a normal domestic vacuum cleaner uses) to pull more than a few PSI against a closed air mass. A real vacuum pump needs a piston pump, multistage turbine, etc. And to vaporize water at "room temperature" you have to get down down to something like .5 psi, or around 29Hg of vacuum. That's actually a little more than is usually possible to achieve with something like a converted appliance pump.

(I know there's this video on Youtube showing a guy collapsing the walls of the "Spun steel pan" that makes up his homemade vacuum-cleaner-powered chamber but... there's a lot fishy about that video, and notable by its absence is a vacuum gauge. I'm thinking that's a *really* light gauge pan; even a pressure difference of a few PSI can deform something like that and that sort of pressure is of marginal use even for degassing castings. Vaporizing water? Fuggettaboutit.)

Vacuum cleaner companies love parlor tricks like picking up bowling balls with their vacuums but the notable thing there is that they always attach a *funnel* to the end of the hose. If their vacuum can pull even 1 PSI and they use a funnel 6 inches in diameter that's plenty enough to pick up a 12 pound bowling ball. A cleaner powerful enough to evacuate a vacuum chamber would have to be able to pick up that same bowling ball simply by pressing the crevice attachment snugly against it. That would be one scary vacuum cleaner.

(Edit: Granted technically you might indeed be able to somewhat accelerate the drying out of an object by putting it in a partial vacuum but you could get the same effect simply by raising the temperature a few degrees. Either way if you're putting the object in a sealed container you'll need to have some sort of desiccant in there with it to capture the water once it's out.)

 

Brooklyn

Well-known member
So I finally got around to baking my PB180 display.

I cooked it for 30min at 190 and 90min at 180. 190 seemed a little hot to me, but actually it was fine.

The screen had no damage after the baking. The tunnel vision effect is reduced, but not eliminated. It is slowly coming back the longer I leave the system running. After 1 hour it is really noticeable.

I think I'll try another couple hours at 190 tomorrow and see if it helps more.

photo (93).JPG

 

techknight

Well-known member
at that temperature, youll probably need to bake that thing for several hours. I recommend a dedicated toaster oven for this.

 

Brooklyn

Well-known member
I ran it at 190 for 4 hours today, screen is further improved. After running laptop for hour + the tunnel vision is minor. I think this is the best it's going to get. The screen looses some "sharpness" after running for the hour also.

 

barrakuda

New member
hello, are there any more updates regarding fixing this "tunnel vision" issue? I recently got a PowerBook 180 with this issue.

 
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