A similar thing happens (or happened, fingers crossed) to my machine. When purchsed, everything was fine. Shortly after, it started with the startup problem. I get a different garbage screen than you, but similar problems. Power cycling generally doesn't help, but after 1-5 minutes it'll reset on it's own and everything is fine. I sent it off to cdjump. He had it working fine for him, but it still did it every so often. Then all of a sudden, the problems just stopped and has pretty much come up 100% of the time first try.
With my MCR PS +5 maxed, I can only get about 4.95 VDC on my SSIO board and when it's up that high the game plays but all the sounds are way off (high pitched, cut in/out). I actually have to lower it so that it's ~ 4.85 VDC for it to play properly. I know this was very little help to you in solving the problem, but 30 years will do quirky things to electronics. If cdjump doesn't think a new switching PS will solve the problem, I'd take his word for it. You could look for a cheap MCR and try it out.