This post is a retro post on a retro topic – a repair I did in 2017 on a monitor made in 1991. I got a question about (probably) the same problem in another venue and realized I never put it online. I managed to dig up my pictures and notes, so there is useful information to be shared.
The end of my (2016) post about Recapping my Macintosh LC I discovered that my matching Apple 12″ Macintosh RGB Monitor ( M1296 ) was going pear-shaped, and speculated that I’d need to recap it.
About a year later, I got around to fixing it. Unlike the LC itself, the M1296 is distinctly not designed to be easy or tool-less to service (that’s fair, it’s a CRT). It has some awkwardly recessed screws, clips around the opening edge, and un-keyed connectors that make it challenging to work on. I found a couple tips on the Internet (one from techknight who had the same problem plus some cascading damage and posted video of their diagnosis/repair) that the most likely culprit was a 2200μF 6.3v electrolytic at C418 on the main board, and ordered some 2200μF 10V caps to replace it ahead of time.
Those tips were good, there was a pool of capacitor goo around C418 and no other visible damage. I removed the remains of the original cap, cleaned the board out out as best I could with Isopropyl alcohol, and put in one of my replacements, and it has been working fine since.
I found a 2019 post from JBRetro with a full Re-Cap list for the M1296, and they had the same known bad capacitor, so it seems to be a repeatable weak point.