Zenith System 3 - jumpy picture with some game consoles

[RetroHacker]

My daily watcher is a Zenith System 3 console (model SM 2535X7). I have it hooked up to several different devices, and it works with pretty much everything (VHS, Beta, LaserDisc, DVD, etc), but I've found that some game consoles - such as the PlayStation or the Super Nintendo - will produce an unstable, jumpy picture. Other games, like the original NES, Gamecube, and most other things - seem to work just fine.

I've done a bit of reading, and found mention of problems with the Playstation and certain Zenith sets. Something to do with the countdown IC for H and V drive not being able to cope with the signal from the game. Is there any fix for this? Any modification I can perform that'll let my set work with more video sources? I need to overhaul the set anyway and replace a few capacitors, so I might as well try to solve this issue while I'm in there.

-Ian