The end of a PB170 LCD?

[techknight]

Ya, i know what you meant.

That was just my crazy idea tangent. I get those from time to time.

But for basic situations, you could get a 6V or so adhesive backed LED strip that you can put in place where the CCFL used to be. And then disconnect the inverter out of circuit.

And put a regulator circuit in place of where the inverter used to be, so you can adjust LED brightness with the original brightness pot

 

[trag]

No.... I never had the "tunnel vision" What I had was a dark screen that the contrast adjustment would not restore, barely enough to see, but not enough to use, but it did exempt tunnel vision like symptoms. but that was because the contrast was too low i think.

Thank you. Hmmm. Well at the risk of derailing the thread, do you have any idea what causes darker areas around the edge of an LCD screen? I looked at the screen last night and it's not actually dark, it's just dimmer around the edges than in the middle. I've also seen LCDs that look like they have a bruised spot in the middle, where the image is slightly darker/dimmer than on the rest of the screen. I've never mananged to imagine what could cause such effect in LCDs.

 

[techknight]

I haven't personally witnessed this myself, but usually the first thing to suspect is bad polarizing film. you can purchase replacements, but not cheap. the adhesive is probably degrading causing the issue. in RARE cases, the actual liquid crystal is going bad, although the liquid crystal if pure does NOT degrade. only if there are impurities in place.

 

[tomlee59]

Thank you. Hmmm. Well at the risk of derailing the thread, do you have any idea what causes darker areas around the edge of an LCD screen? I looked at the screen last night and it's not actually dark, it's just dimmer around the edges than in the middle. I've also seen LCDs that look like they have a bruised spot in the middle, where the image is slightly darker/dimmer than on the rest of the screen. I've never mananged to imagine what could cause such effect in LCDs.

From what I understand, the "progressively darkening corners" problem is due to poor edge seals, allowing moisture to contaminate the liquid crystal. This phenomenon first showed up in the active-matrix 1xx Powerbook series. Allegedly, the damage is somewhat reversible by doing a long, elevated-temperature bake inside a desiccated atmosphere. I've not had the patience to run a clean experiment to verify whether that method actually works.

 

[techknight]

depends on how elevated you let the temperature go.

otherwise youll melt the polarizing film, the buffer drive cables, and possibly the t-con.

 

[techknight]

Also if the theory is correct, the best action to take with the remaining LCDs that dont exibit this symptom, is to run a new bead of VacSeal across the seam of the panel. This should help.

 

[tomlee59]

I haven't personally witnessed this myself, but usually the first thing to suspect is bad polarizing film. you can purchase replacements, but not cheap. the adhesive is probably degrading causing the issue. in RARE cases, the actual liquid crystal is going bad, although the liquid crystal if pure does NOT degrade. only if there are impurities in place.

The symptoms are hard to reconcile with the "bad polarizing film" theory. The darkening worsens as the thing operates. But if you turn off the computer and let it sit, the LCD often looks fine the next time you turn it on, and then degrades again over a tens-of-minutes time frame (typically). In the corners. By a process of Holmesian winnowing, one is led inevitably to conclude that it is in fact the liquid crystal itself. LCs are quite easily poisoned by water. Indeed early LCD work was frustrated by the difficulty associated with removing all sources of water (both initially, and from chemical reactions that liberate small amounts of water over time). A famous story from the early days tells of RCA's woes when researchers ordered "medical grade" liquid crystals, thinking this would be the good stuff. It was full of water, and their displays had short lifetimes.

 

[tomlee59]

Also if the theory is correct, the best action to take with the remaining LCDs that dont exibit this symptom, is to run a new bead of VacSeal across the seam of the panel. This should help.

That sounds like a good thing to try, I agree. Thanks for the suggestion.

 

[trag]

From what I understand, the "progressively darkening corners" problem is due to poor edge seals, allowing moisture to contaminate the liquid crystal. This phenomenon first showed up in the active-matrix 1xx Powerbook series. Allegedly, the damage is somewhat reversible by doing a long, elevated-temperature bake inside a desiccated atmosphere. I've not had the patience to run a clean experiment to verify whether that method actually works.

Ooops. Didn't see the reply for a while.

Thank you, tomlee for your, as always, thoughtful response. I could develop ambitions to try a bake, but given that these displays are from around 2000, and the low price of new ones, I don't think it would be worth the effort. It's easier to just set the computer to do 1152 X 864 and put the display in the mode where it displays the pixels it's sent, rather than trying to enlarge them to the whole field. That way I just don't use the area around the outer edge (native res. is 1280 X 1024).

If it was just capacitor replacement, I'd probably take a shot at repair. It's a little bit of a pity, as these are old IBM (made by Samsung, I suspect) displays and the evenness of the brightness is better than anything I've seen on affordable (to me) modern day displays.

What about the 'bruising' sometimes seen in the middle of displays? Is that likely to be water somehow getting to the middle, or the polarizing film delaminating, or something else? I had an Apple 17" Apple Studio Display with two "bruised" spots, but I sold it on Ebay a long while back. I bought it on Ebay as a 20" Cinema display, discovered the seller was hallucinating, got a resolution and then sold it. Hmmm, let's see, I might still have my picture of the bruises on line, that I used when selling it...

Ah, here we go:

http://www.io.com/~trag/selling/AppleStudioDisplay/spotgrayfront.jpg

http://www.io.com/~trag/selling/AppleStudioDisplay/spotgrayside.jpg

at about 2:30 and 4 O'clock from the apple in the center....

Just read down further: Techknight thank you for your thoughts as well.

 

[techknight]

Well, i had an old crap 17" no-brand LCD monitor do the same thing. turns out, it was excess pressure against the panel from the backlight. (bulging plastic).

But sometimes i guess the panel could get an air pocket? and have the same effect? not sure.

But its the same mysteries that ive seen some LCD panels that have gotten cracked, and STILL worked with no signs of liquid crystal or electrical damage. Because usually the crystals escape and/or electrical connections are broken.

 

[coius]

I saw that. Someone out at a company my dad had as a client when he worked at honeywell, someone jammed a pencil through the LCD when they got mad. After pulling it out, the screen worked as usual, except there was this small mark and spider cracks going out from the pencil area. In fact, except for the small hole where the pencil went through, even the panel behind the spider cracks were displaying. It was the weirdest things, which makes me wonder if there was a hard glass/plexiglass panel in front of the actual LCD that was designed for a buffer. Keep in mind that this was a heavy duty LCD monitor, and was built for hard environments, but it's weird as it looks like it want all the way through to the difuser panel behind the LCD.

Truly an oddity but hey! it still worked!