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Macintosh Portrait Monitor - Bizarre Display Issues

warmech

Well-known member
After finally getting around to putting a cable together to test out my portrait display, I got it hooked up to my IIsi and... well, it sort of worked. And I stress "sort of." It's displaying an image, but the screen has this sort of pulsing effect, where the image will darken in a wave across the screen and then return to expected brightness as the wave passes. The brighter I make the image, the more reduced the effect; of course, with everything overdriven, the image is terribly blown out. I'm attaching a video for reference because I really don't know how to adequately describe what's going on. I'm used to working on much simpler displays (standard-res 15KHz monitors for arcade games) that have pretty well known and addressable concerns, but this kind of issue is entirely new to me. I've got the display broken down and have been looking over the boards with a fine tooth comb and, so far, nothing looks amiss. My first guess would be caps, as they're the most failure-prone components on any display of this age; they all look in decent shape, but that's no positive indicator. One thing I will say - there are a TON of caps; combined, all the boards have something like 60-ish electrolytic caps.

If anyone has any insight on where to start with this thing, I would be beyond grateful.
 

Attachments

  • IMG_3155.mp4
    3.1 MB

warmech

Well-known member
Quick update - it's fixed! No photos/video at the moment, though; the whole thing is completely disassembled and it's not easy to get a good shot of it running. That said, the entire thing (aside from the neck board), has been recapped and this appears to have fixed the issue.

I started with recapping the power/sweep PCB, thinking that something might be awry with the circuitry driving the CRT. None of the caps looked terribly questionable, but this display had been sitting in a non-climate-controlled warehouse in Houston for years; there's no telling what kind of heat and humidity this thing had been subjected to. There were 35 caps to replace on the power/sweep board, but none of them were directly responsible for the issue. Needless to say, this took way too long to complete, lol.

Next were the caps on the video signal board. There were 31 in total and this thing was much easier to work on than the other PCB. For one thing, it was about the size of a DVD case (the sweep board is about 10" by 12"); for another, it had no large or protruding components, which made it very easy to position when soldering new caps in place. Once everything had been replaced, back in it went and everything was working great! The image is stable (with a tiny little amount of pincushion that I can iron out later) and has no artifacts, smearing, etc. In retrospect, I should have probably suspected the video board first and foremost, as adjustments to the gain, bias, and sub-brightness controls (on the video board) directly affected the smearing and pulsing as seen in the video; I feel kind of dumb for not catching that sooner.

In any case, I'll have some images/video of it tomorrow, along with a complete capacitor list and Mouser project link for future reference in case anyone needs to work on their portrait display.
 

slomacuser

Well-known member
In any case, I'll have some images/video of it tomorrow, along with a complete capacitor list and Mouser project link for future reference in case anyone needs to work on their portrait display.
That would be very welcome, thanks. I have two of these displays but for now they are working without problem.
 

ScutBoy

Well-known member
That would be very welcome, thanks. I have two of these displays but for now they are working without problem.
I would be interested in the cap/project list as well - I have a portrait display that is for for the time being, but probably worth the preemptive maintenance before anything goes south.
 

warmech

Well-known member
Sorry for the delay - just started a new job and it was a stressful first week. Below is the end result, and I think it looks great. I still haven't had time to adjust the pincushion, but I may do that later this afternoon. The cap list and Mouser project are as follows; where suitable on the Mouser project, caps of lesser voltage have been bumped up to the next higher value (e.g. 10v to 16v) in order to meet price break quantities:

Mouser Project

Chassis (Sweep Board)Signal BoardNeck Board
C921: 470uF 10v
C926: 100uF 16v
C918: 3300uF 16v
C722: 33uF 16v
C740: 100uF 16v
C919: 1000uF 16v
C670: 47uF 16v
C663: 22uF 16v
C743: 1000uF 16v
C624: 10uF 16v
C718: 10uF 25v
C917: 1000uF 25v
C927: 22uF 25v
C623: 10uF 25v
C604: 1000uF 25v
C923: 4.7uF 50v
C734: 1uF 50v
C924: 1000uF 50v
C621: 47uF 50v
C612: 100uF 50v
C742: 1uF 50v
C601: 1uF 50v
C704: 1uF 50v
C706: 220uF 50v
C909: 47uF 100v
C905: 10uF 100v
C914: 220uF 100v
C915: 220uF 100v
C924: 47uF 100v
C916: 100uF 100v
C622: 4.7uF 100v
C710: 220uF 100v
C653: 1uF 100v
C717: 4.7uF 250v
C100: 330uF 400v
C322: 100uF 10v
C302: 100uF 10v
C356: 220uF 10v
C326: 33uF 16v
C310A: 470uF 16v
C310B: 470uF 16v
C32: 47uF 16v
C30: 100uF 16v
C301: 100uF 16v
C334A: 470uF 16v
C334B: 470uF 16v
C332A: 470uF 16v
C332B: 470uF 16v
C307: 10uF 16v
C325: 33uF 16v
C327: 10uF 16v
C304: 10uF 16v
C36: 100uF 16v
C503: 47uF 16v
C506: 100uF 16v
C313A: 470uF 16v
C313B: 470uF 16v
C316: 470uF 16v
C312: 100uF 16v
C308: 100uF 16v
C513: 47uF 16v
C510A: 4.7uF 250v
C510B: 4.7uF 250v
C505A: 4.7uF 250v
C505B: 4.7uF 250v
C331: 4.7uF 250v
C353: 47uF 16v
C349: 33uF 100v
C507: 33uF 100v
C321: 4.7uF 160v
C508: 4.7uF 250v
C330: 4.7uF 250v

IMG_3202.jpg
 
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CircuitBored

Well-known member
Fantastic job! I crave one of these displays. I think they're a really special product.

Start looking for a new flyback transformer. Yours isn't showing any sign of failure yet but it will some day. It's inevitable. They're often rather hard to come by and you don't want to end up waiting weeks/months for one to show up if yours suddenly dies! I've got new flybacks on standby for my Studio CRTs and it's much nicer to use them safe in the knowledge that any failure is easily repairable.
 

tattar8

Well-known member
Apologies for the necro-bump, but by any chance did you get any photos of the display with the back off? I have mine disassembled and recapped, but am not sure on the orientation of some of the connectors going to the analog board, and the pin numbers are marked only on the boards and not on the cables..
 
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