CTM644 continually rolling fixed

[Bignumbas]

My CTM644 which only had a dead 12v output when I got it suddenly developed a problem with vertical rolling.
It became really sensitive to adjust and when it was finally stopped after a minute or so it would start rolling again.
After Googling the problem for a while I became convinced that nobody knew how to fix this particular problem.
Evidently replacing the V-hold pot doesn't make it go away, I had sprayed it with contact cleaner to no avail.
I tested it with several CPC's to make sure it was a screen problem not a computer problem.
I checked all the caps and resistors associated with the vertical control circuitry, all good.
Reading up on it had suggested sync issues with crt screens.
I checked the newly installed din plug on the screen. I had replaced the old one because it had a broken wire in the lead.
Then I though "what about the LA7800 chip?"
I took one of the 8 spares I now have, replaced the original chip and the screen went crazy when I powered up the 6128 I was using.
That's weird I thought, maybe its a bad chip so I tried another, same thing, getting weirder now.
Then I ended up with a gray box on black. WTF! 5v out was good, 12v out was good.
That's a memory problem, my test machine had died at the precise moment I changed the LA7800.
Grabbed another machine to test the monitor, perfect!
No more rolling, its been running for a while now and the problem is gone.
Weird stuff happens sometimes when you are fixing things.
Now I have a 6128 to repair, again!

[Bignumbas]

The 6128 had one dud memory chip that failed, good thing I put sockets in when I replaced them.
One bank was populated with the original chips though, that's where the failure was.
Everything works now