PowerBook 160 Bleached / No Contrast Screen

[Spode]

I touched on this in a previous thread (https://68kmla.org/bb/index.php?threads/odd-bodge-wire-on-powerbook-160.40023/) but it would likely have been lost by the misleading topic.

I have a working PowerBook 160, but the screen is not behaving. When I first got it - no matter what, I got absolutely nothing showing on the display. I recapped the display and saw an improvement - I could at least now see something on screen when the display was set against a piece of paper, but the minute I re-assembled, unless I throw the let hand control (contrast?) all the way to the bottom, I can't make anything out.

After another suggestion I recapped the inverter board. Despite what looked like some possible gunk they tested okay enough on the ESR, so it's no surprise that I didn't see any major improvement.



My phone camera doesn't seem to capture it very well as I think it's auto-compensating for the white balance and making it look like it has more contrast than it does, but this is a fairly good idea of what I'm dealing with.

My first thought is that I'm assuming contrast is controlled by an an analogue voltage signal - does anyone know what pin that is on, and what the voltage range should be? That seems like a good thing to check.

 

[desertrout]

Hm. Not sure what it could be --- have you cleaned the brightness / contrast pots? Verified your replacement cap values? (grasping at straws)

 

[Spode]

Hm. Not sure what it could be --- have you cleaned the brightness / contrast pots? Verified your replacement cap values? (grasping at straws)

I have cleaned the pots.

My current thinking is this. I didn't have any 3.3uf caps so I used 4.7s as I felt they would be within tolerance. They were fine on my 145, but then that's a monochrome display. With 16 greys it might be more sensitive.

So I've ordered some new caps (frustrating how most places have a minimum order or sky high shipping) and I'll recap to eliminate it as an issue.

 

[desertrout]

Interesting... really curious to know if that's the issue!

 

[Spode]

Process of elimination! It is strange though because before the recap it was a similar problem really, which makes me think there is another cause. It doesn't actually look terrible anymore if I slam the contrast all the way to the bottom, so I may end up compromising with that.

I keep wondering if a small resistor on the contrast signal might help, but I'm not sure if that would make a difference to a PWM signal?

 

[Spode]

I've now replaced the caps. I'm still getting the same effect - but it seems to go away once I get into the OS. I know from what I've read there is a software aspect to the brightness/contrast controls as well - so something is clearly sorting itself out. It's possible the re-cap did nothing.

However, I'm seeing more lines/shadow than I would expect. Granted, I've never worked with a 160 before and I know these passive matrix screens were never great. Does this look normal to you? Ignore what looks like some odd moire caused by resizing of the image - I'm talking about more about the box that seems to surround the words "Trash".

 

[AndyO]

That does look somewhat normal to me for a passive matrix screen. The white 'box' is delineated by the ends of the hash lines in the title bar to the left and the right of the word 'trash', not by the word itself, and by the lower edge of the upper segment of the display. You likewise see the same effect around the close box for the window on the far-left.

You can normally adjust these ghosting effects out to some extent with brightness and contrast but usually not completely. It's the result of high contrast edges, and is even more notable when using some software (Word 5.1 for example) than others, due to the composition of screen elements such as window content, toolbars etc.

These type of screens were much like this when new - hence the fairly rapid move to active matrix designs as they became available.

 

[3lectr1cPPC]

I tried to replicate your desktop setup on my recapped 145, which should have just about the same display, and it looked like this:
I don’t see that box around the trash text, but I have more artifacting around the trash icon itself. It could just depend on the particular panel, perhaps some artifact differently than others? I was also using a different desktop pattern as I couldn’t find the same one on my install, so that could have affected things. Lighter desktop patterns seem to show less artifacting than darker ones though.

 

[Spode]

Macintosh PowerBook 140 / 145 / 145B / 160 / 165 LCD Display Recapping Guide – Mac84

mac84.net

When I look at "after" pictures here, it feels like that is considerably better than what I have.

I have a second PB160, so I just re-capped that screen (same issue - nothing coming up) and the result is almost identical.

I switched mine out, like for like electrolytic. I also did the invertor board. I can't help but feel there's something I'm missing. @Mac84 - any thoughts?

I have a 145 as well, as the the effect is far less noticeable - closer to what you are seeing on yours.

 

[Spode]

I found this footage of another 160 and it looks 1000x better.

I've added a couple more pictures to emphasise.

What's interesting is if I switch it to 2 or 4 colours in the control panel, it looks great!

I also feel like I'm seeing some overall shimmering on the display which does suggest to me there is a capacitor somewhere that I'm missed and that one's highlighted are not enough.

 

[AndyO]

I have a 145 as well, as the the effect is far less noticeable - closer to what you are seeing on yours.

The 160 and 145 don't have the same display. The 145 is a monochrome panel, and in my experience, my 145B (also monochrome) shows far less distinct ghosting artifacts than my 165 (also greyscale).

I also feel like I'm seeing some overall shimmering on the display which does suggest to me there is a capacitor somewhere that I'm missed and that one's highlighted are not enough.

My 165 shimmers badly when in greyscale mode, and rather less noticeably so in monochrome.

I would add that neither my 145B or 165 are recapped as yet, and your 160 images look much like my not yet recapped 165.

 

[Johnnya101]

It should look bad, but not that bad. Definitely something you're missing.

 

[Spode]

It should look bad, but not that bad. Definitely something you're missing.

That's exactly my thought. The question is - what? I'm not really sure what to try next and they aren't exactly the easiest things to work on as you have to keep reassembling etc.

I now have two PB160s presenting in exactly the same way.

 

[3lectr1cPPC]

Would you mind posting a photo of the capacitors on the display you replaced?

 

[Spode]

Would you mind posting a photo of the capacitors on the display you replaced?

If I end up opening it up again - more than happy to. I'm not arrogant enough to assume I didn't mess something up. I did exactly the same as I did when I recappped the 145 (which seems fine). Removed the old ones, clean it up with IPA, then solder in new ones using some flux/solder paste. They all seem to have solid connections.

Unsure if related - but I decided to test the caps on the invertor board (the ceramics) and the orange one at c7 won't get picked up by my ESR meter, or multimeter.

If that's gone, might be having an effect.

The red one tests as "leaky / in circuit". Granted it IS in circuit, so might not be a good reading.

Tempted to try swapping those out, but I don't think I have any replacement ceramics. Any reason I couldn't put a radial electrolytic there instead?

 

[3lectr1cPPC]

Changing capacitor types usually doesn't screw anything up - I recapped my 145 with ceramics, but I'm definitely no expert on that.
Can you post a photo of the capacitors on the display itself that you replaced? That's where I would look first when it comes to abnormal levels of artifacting and ghosting.

 

[Spode]

Would you mind posting a photo of the capacitors on the display you replaced?

Hard to get good angles - not sure what specifically you are looking for. It does look like maybe of the legs isn't happy on C3 - but I find it hard to believe I'd have made exactly the same mistake on both screens.

 

[Spode]

So on C3, it turned out to just be a blob of solder that shouldn't have been there but wasn't affecting anything.

I touched up all the caps and then did a continuity test on the pads to make sure they were connected properly. I also measured a sample of my cap using my ESR meter and they were all within spec.

BOTH of my PB160s had the same issue - literally nothing on screen. So it's entirely possible that if there is a fault beyond the screens - it's present across both.

But, still, brings me back to - what the hell do I try next...

 

[3lectr1cPPC]

That looks very clean, I don't see any obvious issues there.

I have an IBM PS/Note 425 laptop from 1993 with a grayscale passive matrix display (also recapped with ceramics), and it also has much worse ghosting than the 145's black and white display. However, it still isn't THAT bad.

I hate to say it, but I'm officially out of ideas
All that I can think of is to give an extra good cleaning to both display boards (not the inverter board), and try again. I'm leaning towards a different, unknown issue after what you've said though.

 

[Spode]

That looks very clean, I don't see any obvious issues there.

I have an IBM PS/Note 425 laptop from 1993 with a grayscale passive matrix display (also recapped with ceramics), and it also has much worse ghosting than the 145's black and white display. However, it still isn't THAT bad.

I hate to say it, but I'm officially out of ideas
All that I can think of is to give an extra good cleaning to both display boards (not the inverter board), and try again. I'm leaning towards a different, unknown issue after what you've said though.

Very clean? No. Clean enough? I think so.

I've just switched the invertor board with the one from the 145 - no difference at all.

I gave it a thorough clean up, and even removed a component that looked like it might have some gunk underneath it and put it back, no difference.

Looking up the values for those ceramic caps on the invertor - they are very low (nf) and it's possibly my ESR meter can't detect that low. My understanding is those kind of caps don't tend to fail either.

Maybe I should take this over to BadCaps for some more general electronics advice to diagnose further?