It looks like the PSU is hiccuping. First up, I'd try unplugging the grey ribbon cable to the CRT board to isolate it from power to check it's not still bad somehow.
Have you replaced C17 in the PSU with a new low ESR cap? These are *always* in need of replacement, and can take out a few other parts if left alone..
Check a few other parts as per this image to make sure the standby power is ok:
There are a few known problems with old capacitors in these PSU's, and being an A model, it will be older and the capacitors nearer the end of their life... I have personally found a couple PSU's needing a complete set of replacement capacitors in older scopes.
Are you located in Japan? I have a bunch of spare parts for these scopes including working PSU's and CRT boards, so it wouldn't be difficult or expensive to figure out a trade etc.
Jared
Jared Cabot