The end of a PB170 LCD?

RIP, PB170.

But at least now you have parts for the other one.

RIP, PB170.
But at least now you have parts for the other one.

Click to expand...

Bah this pains me! My powerbook stack continues to shrink as the years march on! I have gone from 10 working to about 5, and a whole box of Spindlerbook parts. (The 5300/190. Every single one I had (5) died.)

My God, the 5300 seems to have the absolute worst manufacturing quality. 5 dead?!?!?

i just got a 160 from another member here with similar screen issues, and the contrast would drift around as the screen warmed up.

I fixed it. works like a brand new screen too. There was a thread that i made a couple posts in about the same screen issues, and yellow corners, etc and i brought this up. but no one has tried or posted of trying of what i suggested. So i got a powerbook for myself, and tried it myself.

There is approximately a 40V or so supply that provides power to the STN grid itself. when the buffers/drivers scan the display, it sends AC current to each pixel twisting the crystal in one position or another, uses this supply as the B+ source for doing the "twisting"

problem is, this supply gets noisy and lowers in voltage, allowing the screen to do strange things. All the surface mount electrolytics were bad, just as the ones that plague compact macs. I replaced all of these and the screen worked like brand new.

Now this could be useful information. Where were these capacitors located? On the boards located within the screen assembly itself?

Yes, this is an important repair that needs more promotion! Also interested in your fix, techknight - this could save a lot of portable Macs from being thrown. Any pics?

JB

I will take pics when i get a new camera. My trust old Sony DSC-V1 that i used for everything took a shit. It turns on and right back off. strange. If i keep fiddling with it, i can get it to power on to lines in the LCD screen before it shuts back off. MADE IN CHINA.

Anyway, The LCD assembly itself has a DC-DC converter plus the connectors and everything else. it has SMD electrolytics.

When I get another camera, i will do a whole new thread on it. If thats ok.

Cap list:

Qty. 9 3.3uf 35V

1 22uf 35v

1 100uf 6v

You must use SMD electrolytics as replacements, or tants. regular radial patch-ins wont work, there is no space clearance to allow for this.

It would be interesting to see the effect of capacitor replacement on a blackened screen....

I just fixed my trusty old sony DSC-V1. I took it apart and found a couple of bad electrolytics in the DC-DC converter. I wasnt out anything, so i stuck a couple more in and it worked. HA....

So when i get some time ill do some full documentation and pics. because i have 2 more screens to do. no worries.

we are waiting for those picts and info!

Ben

shit i totally forgot. LOL.

I have another LCD i have to do, so it would be easier if i just made a video.

I think backlight is going on my 170 or maybe one of the various boards associated with the display. The LCD works perfectly, but the backlight is now a dim amber. Maybe I could do a LED backlight instead!

my guess it has a bad CCFL tube.

Just to clarify...

On LCD displays which stop displaying around the edges -- they kind of look like something has been nibbling the display around the edges, replacing the SM electrolytic caps inside the display restored them to full functionality?

I have some IBM 18.3" LCD displays from 2000 and a few of them are look like something dissolved/washed away the outer rim of the display when I try to use full resolution. So instead of 1280 X 1024 I must run them at 1024 X 768 to avoid the bad area.

Yes, I prefer a 1280 X 1024 display with pixels in a WYSIWYG size, to the modern wide screen, everything so small you must have the eyes of a twelve-year-old to see it screens.

Also, while these old IBM screens aren't terribly fast by modern standards, the evenness of the display is amazing. Newer displays (at least, the ones in my price range) seem to all have brighter and darker areas, but these old IBM displays are dead even in terms of brightness across the display.

They could stand to be brighter though. I'm guessing that the backlight tubes are down to 70 - 80% of their original output or some such too.

Trag, we need cap kits and colour LED backlight kits. It would be cool to have different colours.

Replace the inverter just for giggles too.

Just to clarify...
On LCD displays which stop displaying around the edges -- they kind of look like something has been nibbling the display around the edges, replacing the SM electrolytic caps inside the display restored them to full functionality?

I have some IBM 18.3" LCD displays from 2000 and a few of them are look like something dissolved/washed away the outer rim of the display when I try to use full resolution. So instead of 1280 X 1024 I must run them at 1024 X 768 to avoid the bad area.

Yes, I prefer a 1280 X 1024 display with pixels in a WYSIWYG size, to the modern wide screen, everything so small you must have the eyes of a twelve-year-old to see it screens.

Also, while these old IBM screens aren't terribly fast by modern standards, the evenness of the display is amazing. Newer displays (at least, the ones in my price range) seem to all have brighter and darker areas, but these old IBM displays are dead even in terms of brightness across the display.

They could stand to be brighter though. I'm guessing that the backlight tubes are down to 70 - 80% of their original output or some such too.

Click to expand...

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.

Recapping the panel restored full contrast/brightness evenly across the screen.

Trag, we need cap kits and colour LED backlight kits. It would be cool to have different colours. Replace the inverter just for giggles too.

Click to expand...

Well, if the LCD was fast enough, but its no where near fast enough, but if it was....

you could use RGB backlight to do field-sequential color and it would appear that the mac would have full color. But the Video adapter doesnt support it, and neither does the LCD response time.

I did this very thing with an old Mac SE CRT and a color-wheel. built a full RGB color field-sequential VGA monitor. Same rule would apply with LCD, if you used RGB backlight instead of a color-wheel.

But the LCD response time isnt fast enough to be able to switch RGB video signaling without extreme flicker.

I meant a single solid colour. If you wanna get fancy, two colours, one for use during the day and one for night might be neat. but make sure you have a switch to turn em off for situations where you do not need a backlight.

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

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.

Click to expand...

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.

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.

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.

Click to expand...

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.

depends on how elevated you let the temperature go.

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

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.

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.

Click to expand...

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.

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.

Click to expand...

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

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.

Click to expand...

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.

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.

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!