Macintosh 16-inch Color Display -- Post Recap Issues

[ktkm]

A couple of weeks ago, I decided to fix minor convergence issues with my Macintosh 16-inch Color Display. Hence, after finding a burnt capacitor on the main board, I thought it was time to have the entire display recapped before I began fiddling with all the potentiometer dials. I started with the video board, which was pretty easy and then moved over to the main board, which was slightly more time-consuming, to say the least. However, when all the old capacitors had been removed except for a few (the big 470 µF 400 V and a couple of bi-polar cans), I noticed that “KEY geometry” had started to wobble ever so negligibly. Focus, convergence, and geometry have improved, but I’m not too fond of the wobble. To illustrate the issue, I made this exaggerated animation.




Has anyone here ever had this issue with a CRT and knows what causes it? Or perhaps have had a successful recap of a Macintosh 16-inch Color Dispaly?

 

[3lectr1cPPC]

I have a problem just like that on my Blueberry iMac Slot-Loader. I assumed it’s caps going bad as well. I’d also like to know what else besides them could cause it if you’ve got the same issue after a nearly complete recap.

 

[ktkm]

Problem solved! It was my own human error!
I took the whole thing apart and noticed I had put one capacitor, “C302 (10µF 50V),” on backwards. It didn’t show from the top of the board, but things became clear when I flipped it over. That particular capacitor sits next to the KEY trim-pot. This is what you get when you start soldering at 02:00 a.m.

I have a problem just like that on my Blueberry iMac Slot-Loader. I assumed it’s caps going bad as well. I’d also like to know what else besides them could cause it if you’ve got the same issue after a nearly complete recap.

After my recent endeavour, I would start looking at components close to the KEY trim-pot area. However, I’m not sure what that would look like on Slot-Loader iMac.

Another thing: I found was a button magnet held by some double-sided tape on the back of the CRT.
Is that common practice for Trinitron tubes of this size?

 

[3lectr1cPPC]

Good to see you got it figured out. I’m really putting off recapping mine as it’s a massive pain to get the analog boards out, and I’m likely to destroy the display bezel trying. I’ll bet it caps though.