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Macintosh Color Display: How did I royally screw this up???

LaPorta

Well-known member
LCD conversion?

Good news is I found one on eBay. With shipping, it was more than I wanted to pay, but I’ll recap this one (with more caution this time) and if it all works out, save the fly back and other parts of the questionable one for the future.
 

LaPorta

Well-known member
Ok here is my update: I pulled the new caps from the first M1212, tested each and every one of them with my ESR meter (all were good), and placed them in my new M1212 - and the exact same symptoms occur. This leads me to believe that there is something about some cap in there that is not the right spec other than capacitance. I have recorded the ratings and series of every cap that I took out. I need to do research and find direct equivalents for each and every series.

At least now I do not have any doubt that I did not break this one, only that there is something with the parts used. Any suggestions, let me know Stay tuned...
 

LaPorta

Well-known member
Ok, big update on this project. Will try and rope in @techknight to see if his genius can shed any light here:

So, I went back to the drawing board. The same caps were causing the exact same symptoms as the first monitor. Too much coincidence to be anything other than the parts I am using (It is virtually impossible that I screwed up the second board the same way as the first. I took each and every one of the caps from the board that were originally there and looked up and documented their series and what sort they were (i.e. general purpose), and noted that three were supposed to be low impedence, high frequency caps. The rest were caps that by their series are supposed to be general purpose. So, I changed those three after ordering equivalent types to what was originally there. The problem seems to still persist. It was actually working ok at first, with a bit of horizontal shift. It was shifted too far left, so I adjusted the horizontal position pot. The second I touched that, the whole monitor went haywire collapsing in on itself, giving the crazy pattern that happened originally.

So, here is what I have concluded thus far if I am correct:

1. The problem lies somewhere with a (or many) capacitors.
2. It likely is not because of any type of high frequency necessary cap (I made sure those were there).
3. One of the remaining caps must be somehow out of spec in a way that I do not understand.
4. The caps are not "bad" (I tested every single one before putting them in this board with my ESR meter).

I am attaching the order sheet for my capacitors that I used on this board, complete with links to the parts themselves to check if they are appropriate. I am also attaching my hand-written sheet that documents what cap, what rating, series, etc. Please note that I had two different revisions of the board I was working with, which accounts for why some caps have "or" and two different series by them. Lastly, I will attach the board schematic so that someone with understanding of how these circuits work can hopefully point me in the direction of what would cause a malfunction such as this. Hopefully the combination of what cap was there originally, what I replaced it with, and the circuit itself will lead to some possible culprits.

Note: CP12, CL14, and CL21 are the three I changed out for exact equivalent series as the originals already.
 

Attachments

  • M1212 Caps.pdf
    317.4 KB · Views: 8
  • M1212 Capacitor List.jpg
    M1212 Capacitor List.jpg
    4 MB · Views: 39
  • AppleM1212MonitorSchematic.pdf
    303.4 KB · Views: 7

LaPorta

Well-known member
Here is some more info. I started it up cold and it seemed to work well. Then, as it warmed up, I adjusted the brightness/contraqst on the front, and then it started going haywire again. Videos attached:
 

Attachments

  • IMG_3437.MOV
    57.1 MB
  • IMG_3439.MOV
    60.9 MB

LaPorta

Well-known member
...and.....it just works?

Really no good way to explain this: the monitor now works without a single issue...for no good reason I can find.

Best I can theorize is that the other capacitors or some component in there were "thrown off" by the non-high frequency capacitors that were in those three spots to begin with, and just "took their time" getting back to normal function. I really have no explanation, but it has worked 100% with no issues at all for hours, I even jostled the board and put the cover back on, etc, to see if there was anything loose that I would cause it to not work...nothing. Not a single flutter on the screen.

If anyone has even a possible explanation for this, let me know. Otherwise...if it ain't broke, I am not going to try and fix it, and just count my blessings!
 

Garrett B

Well-known member
Wow, I missed this thread and am just reading it for the first time. I applaud your tenacity! The M1212 is one of my all-time favorite monitors, so I would feel the same about not giving up. Really interesitng obsrevation about the G and B drives still being alive, just not recieving any incoming signal. I haven't ever opened one of these up, but have you toned out all the connections from the monitor cable pins back to where they end up on the board? Part of the trouble with the integrated cable is that it's harder to swap between monitors and rule it out as a possible cause.
 

LaPorta

Well-known member
I actually gave up on that board and will now use it for parts (has a good flyback, etc). I also managed to ruin the tube by a tiny dot being burned into the center by the electron gun focusing there after it collapsed...so that's done. The second one I thought would be toast...but I think I honed in on the issue that the caps I used in three of the areas were not appropriate for the circuit. I'm going to be much more thorough with my recaps in the future with regard to PSU/monitor circuits. There's a lot more to it than "capacitance/voltage rating."
 

Byrd

Well-known member
Thanks for putting up your adventures, LaPorta - at least you know it's recapped clean and ... working for years to come? One of the nicest Apple CRTs made.
 

LaPorta

Well-known member
Thanks, Byrd. That's its intent: to serve as the main display for my IIfx...hopefully for years. I hope that this all serves as an example for others who might have a similar issue!
 

techknight

Well-known member
Here is some more info. I started it up cold and it seemed to work well. Then, as it warmed up, I adjusted the brightness/contraqst on the front, and then it started going haywire again. Videos attached:
Thats caused by 1 of 3 things. A) Noisy pots, B) bad solder joints, C) Noisy semiconductors.

The issue is purely in the vertical circuit as well.
 

9166188

Well-known member
It could be degraded connection inside the video cable. I had experience similar symptom with my M1212. And got fixed after unplugging the video cable on both ends and reconnecting again.
 

jmacz

Well-known member
@LaPorta how did you determine whether the three caps were high frequency low impedance caps? Asking as I am embarking on recapping a m1298 display, and so far only looked at capacitance, voltage rating, temp, and size. Thanks.
 

LaPorta

Well-known member
The series that is printed on the cap itself. If you see my attached note sheet, you will notice the company and series column. If you look up the data sheet on each series, it will tell you what type of capacitor it is. That is how I determined which needed to be hi freq.
 

jmacz

Well-known member
Hmm, really interesting.

So I finally got around to recapping my M1212. I decided to recap because I was getting some wobbling on the screen and I checked and reflowed most of the solder joints with no improvement.

I replaced all the caps and tried a test, and the wobbling was much worse. It wasn't as bad as @LaPorta 's video above but the picture was pretty wobbly, more on the bottom third of the screen than the top 2/3rds.

I then went back and inventoried my caps as I had specifically purchased high frequency caps for CP12, CL14, and CL21 after reading this thread. <Palm to Face> I had grabbed the wrong ones! The high frequency ones were still in package in my drawer. I then replaced those three with the proper high frequency ones. Powered up the monitor and still, same problem, wobbliness and random shaking (again, not as bad as LaPorta's video). I let it run (wobbling) for about 15 minutes and then powered off the monitor. Rebooted about 5 minutes later and the wobbliness was gone.

That was two days back and I've since powered it on a few more times and ran it for about 15-30 minutes each session, and it's still gone.

???? So confused.

To @techknight's point, I can't imagine it self corrected. Something must still be wrong. Guessing it's a solder joint that is not great and running it for a bit may have done something to get it into a state where it's working for now? Just funny how it played out the same as @LaPorta .
 

techknight

Well-known member
Make sure the monitor isnt near any alternating magnetic fields/EMI sources, ive occasionally found fans, transformers, and other nearby objects to cause CRTs to wobble.
 
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