I finally decided to sign up to the CRT Forum hosted by Curt Palme it seems to have a pretty active CRT projector section and not all of the discussions end up being mirrored on AVS in some way. I’ll likely just lurk, but I intend to at least visit regularly.
There was a post by Scott (tse) who knows a lot about Ampro systems. In one posting he comments:
The six devices attached to the registration amp heatsink have thermal shutdown circuits built in. They will turn off if they overheat. Once cool they will turn back on. So if the green vertical amp overheats the green will jump to the position it is in when registration is turned off. Same for blue horizontal, red vertical…..
Check that the screws are snug, they can loosen over time.
Now in this context he was talking about an Ampro 4200, but I’ve seen this same thing happen with my 4000 and hadn’t put 2 and 2 together. I’ve seen the convergence suddenly ‘jump’ to have a huge drift. Entering the help/setup menu would show that things were not really that bad – I suspect that the setup menus reduced image levels result in the system cooling off somewhat. In these cases – the room temperature had risen quite high – probably a bit more than 30C up at the ceiling.