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180c contrast drifting issue - inverter board caps?

3lectr1cPPC

Well-known member
I picked up a 180c a few months ago. It worked but really needed the screen recapped, so I did that and the picture quality looks better now (artifacting is gone - I had a thread on it a few months back), but it’s got another problem.
When I first turn it on, the screen looks perfect, but it will slowly down the contrast until white objects look dark gray, and readability goes down a lot.
B0256787-5510-469C-B65F-E8DCA691D56F.jpeg
Does this mean it’s time to recap the display inverter board, or is it a different problem? This is an active matrix display, and it has no control for the contrast, neither hardware or in software.

The inverter board has 2 small through-hole electrolytics, and they both look fine. Could 2 small caps really cause this big of an issue?

Edit: When it's starting to drift and go dark, it will "flash" back to normal for a second a handful of times until it eventually just stays dark.

Thanks!
3lectr1c
 
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Byrd

Well-known member
Try a recap, but I'd experiment first with different room temps - thinking it might be an LCD polarizer issue. Try using the Mac in a very cold room and see if you can extend the delay, alternately warm up the PowerBook and test the other way.
 

3lectr1cPPC

Well-known member
When it's starting to drift and go dark, it will "flash" back to normal for a second a handful of times until it eventually just stays dark.
I'll go ahead and give that a try but this behavior would at least to me suggest otherwise. It has been steadily getting worse since I got it, but I'll go give it a go in the 70+ degree outdoors.

Edit: Just tried it but it hasn't been off long enough for it to "cool off" again I guess, because it had the issue immediately. It's also not that much warning outside than inside at the moment so it probably wouldn't have changed much.
 
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3lectr1cPPC

Well-known member
There is also a transformer board in these screens, but these have polymer caps installed and likely do not need to be replaced.
Found this lovely line of text on the console 5 capacitor kit description for the 180c. Assuming the two caps I'm hoping are the cause of my problem are polymers, what are the chances they've actually died? Probably next to zero...
 

3lectr1cPPC

Well-known member
Uh oh, I really, really hope that isn't the case. It doesn't start in the corners though like a tunnel vision display normally would, the whole display goes at once.
When it's starting to drift and go dark, it will "flash" back to normal for a second a handful of times until it eventually just stays dark.
Tunnel vision displays don't do this either. It's been getting worse too, when I first got it a few months ago, I played (well, tried to play anyway, it's too slow) wolfenstein 3D for probably around 15 minutes, along with other stuff and it only happened a little bit. If tunnel vision is caused by moisture, I don't see how it would have gotten this bad after a few months in a dry, dehumidified basement.

From my symptoms, I'd think some component is starting to go and can't "keep up" after a few minutes. Capacitor would make perfect sense for this but if the "transformer board" caps are all polymers, I don't know where else to look. The inverter board inside of the keyboard case doesn't have any caps either.

The guy I bought this from said the display "washes out" after being on for a little while, which I assumed was the bad caps (which I already replaced), but I never ran it long enough pre-recap to see if this happened. I also don't know if this is what he meant.

One thing I'm very sure of is that this is a contrast issue. You know how bad the contrast is on old LCDs, if you look at them at an angle the colors you see change. Well, when it's not gotten that bad yet, if I look at the display from an angle, it looks completely normal (due to the color shift from the angle).
 
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techknight

Well-known member
Uh oh, I really, really hope that isn't the case. It doesn't start in the corners though like a tunnel vision display normally would, the whole display goes at once.

Tunnel vision displays don't do this either. It's been getting worse too, when I first got it a few months ago, I played (well, tried to play anyway, it's too slow) wolfenstein 3D for probably around 15 minutes, along with other stuff and it only happened a little bit. If tunnel vision is caused by moisture, I don't see how it would have gotten this bad after a few months in a dry, dehumidified basement.

From my symptoms, I'd think some component is starting to go and can't "keep up" after a few minutes. Capacitor would make perfect sense for this but if the "transformer board" caps are all polymers, I don't know where else to look. The inverter board inside of the keyboard case doesn't have any caps either.

The guy I bought this from said the display "washes out" after being on for a little while, which I assumed was the bad caps (which I already replaced), but I never ran it long enough pre-recap to see if this happened. I also don't know if this is what he meant.

One thing I'm very sure of is that this is a contrast issue. You know how bad the contrast is on old LCDs, if you look at them at an angle the colors you see change. Well, when it's not gotten that bad yet, if I look at the display from an angle, it looks completely normal (due to the color shift from the angle).

Well its possible you have an open via/intermittent connection from cap goo on the display itself when it was recapped. You need to take a look at it.
 

3lectr1cPPC

Well-known member
Thank you for the help. I’ll do some probing for bad connections when I have time. Here’s a thought though - right on the opposite side from the board from the caps are around 5 or 6 voltage potentiometers (I believe so anyway, I can’t post photos later). They had really bad cap goo on them and the joints look a little corroded, even after intensive cleaning. I wonder if there’s a bad connection there and/or an issue with the potentiometers drifting after it’s been on for a while. Would it hurt to try adjusting them while the computer is running, or would that risk breaking the panel?
 

techknight

Well-known member
Thank you for the help. I’ll do some probing for bad connections when I have time. Here’s a thought though - right on the opposite side from the board from the caps are around 5 or 6 voltage potentiometers (I believe so anyway, I can’t post photos later). They had really bad cap goo on them and the joints look a little corroded, even after intensive cleaning. I wonder if there’s a bad connection there and/or an issue with the potentiometers drifting after it’s been on for a while. Would it hurt to try adjusting them while the computer is running, or would that risk breaking the panel?

If it was that bad, then the broken connection can be anywhere. I bet while powered up, if you push/manipulate this area, the fault will come and go.
 

3lectr1cPPC

Well-known member
I’m curious about that too, I feel like pressing in a certain spot made it flicker in and out of the issue - that was with the front bezel on though, I’ll have to try that when I have time - I have a super busy week ahead though so it might be a while.
 

3lectr1cPPC

Well-known member
Apparently they are solid polymers, not electrolytics that commonly fail. Polymers will last much, much, much longer.
 

3lectr1cPPC

Well-known member
Hmm, good to know. They look fine, but I'll get a picture of them this weekend, along with pictures of my display PCB to hopefully help troubleshooting, just don't have the time right now I'm afraid.
 
I have what seems to be the exact same problem. I'm pretty sure the problem is NOT the inverter board. Why? I switched the screen (just the screen) with another 180c I own and the problem "follow" the screen not the inverter board. I also notice on THIS screen a black "something"around (I suppose) a resistor near to the caps that I'm pretty sure was no there before. Maybe this tiny resistor is gone now, if it is a resistor... I'm not really an expert.

Just to be sure about your problem: if you look at the screen from another angle, does the screen looks better? I mean better... gray more white, not really better.
 

3lectr1cPPC

Well-known member
Just to be sure about your problem: if you look at the screen from another angle, does the screen looks better? I mean better... gray more white, not really better.
Yes! It does look better at an angle! Thanks for confirming the inverter is probably ok… What’s the silkscreen for the resistor? I can crosscheck on my LCD
 
The black "something" (that I clean away with isopropyl) was around the two resistors (are they resistors?) showed in the picture, more on the left one.
I do not know how to check/test them anyway... if you do (or someone does) let me know.
This is not my real board... just to show you what I'm saying. On mine contacts seems to be darker than normal, but not so bad. If I re-open it I'll post the real one.
Is just a clue, not an evidence. Let me know if you find out something

Schermata 2022-06-03 alle 20.50.14.png

Schermata 2022-06-03 alle 20.50.14.png
 

3lectr1cPPC

Well-known member
The darker then normal would be corrosion I’d imagine, probably not an issue as long as they’re still connected.
 

3lectr1cPPC

Well-known member
Not to call victory too early but I think I found the problem…

So, I was going about trying what @techknight suggested about poking at the board while it’s running. So, I took the front display bezel off and turned it on to find that as soon as the display finished initializing (the initial white screen went away, aka the computer took over control), it instantly went dark gray. I decided to mess with the voltage pots. Upon adjusting the pot labeled “V7”, it went away. I found that shorting any part of the pot to ground caused the display to go all gray again. The legs on it are a bit corroded so it’s probably a bad connection. For now, I’ve had it on for several minutes and the display looks perfect. If the issue comes back I’ll try to remove, clean under, and resolder the V7 pot, but it’s good for now!

Why don’t you give that a go @mattia1071 and see if it fixes your issue!
7B4722FF-5007-4706-BC64-2AB9AE6B5AB5.jpeg
57F55ADD-3CA3-431B-B647-E2A9630216B1.jpeg

Edit: I've had it on for around 20 minutes now and there's no sign of the issue! I think this one may be fixed!
 
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Hello and thanks for the advice.
A strange thing happened to my screen. As I explained, when the contrast had given problems, I swapped the screen with that of another 180c and the problem had "followed" the screen into the new computer. After a couple of days I switched on the PB180c and the contrast worked properly again, in short the problem disappeared on its own. I don't know if what happened to you could have happened to me, but it's good to know that the problem can be solved. I will look at the potentiometer to see if there is a problem in mine too.
Initially my theory (but I'm not a technician) was that since I hadn't replaced the capacitors yet, once they had 'cooled down' for a while, they started working properly again. Given the new information I received, my theory was probably wrong. However, I plan to do a recap soon for the colour problems (shading and artefacts) without abusing the old condensers which I am afraid are starting to leak (you can smell the classic fishy smell, even if only slightly).
Your information also gives me another relief, I thought it might have been the motherboard that caused the problem with screen no.1 and I was afraid that after the screen swap, it might also have damaged screen no.2, the healthy one. Evidently this is not the case.
 
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