Mikko has written an article about Marconi 2955A repair:
First off, I decided to see what was the deal with the CRT. I have never worked on CRTs before, I have understanding of how the picture is formed by steering the electron beam using the deflection coils but that’s about it. I know a charged CRT can be deadly so I took my own safety very seriously. After carefully removing and inspecting the CRT drive board AC1, I noticed that someone had been there before. There were telltale signs everywhere. Screws missing, protective plastics missing, horrible soldering jobs… The CRT-to-chassis grounding strap appeared to be on but when I touched it ever so slightly, it just came off. I also noticed a TO-220 transistor (vertical deflection control) had apparently been changed by cutting off the leads from the old one and badly soldering a replacement on.
More details at Mikko’s blog.