Amiga 1200 crashing and freezing

[Merc]

That sounds like the problem where if there were any colours onscreen that were full-white, ie 255,255,255, the gfx would get corrupted after a few minutes -- my brother's 1200 had this problem, but mine didn't.

We "fixed" it by writing a little program that watched the current screen and changed any colours that were full white to 254,254,254 instead, and that, believe it or not, fixed the problem!  :-D

[Merc]

Now THAT'S one I've never heard of!  Quite an odd solution, too!  What little I know about the real electronics of how computers work would lead me to believe that is an artifact of one of the 'timing errors' that are discussed for the 1D3,1D4,2B motherboards.

Well your description of the problem (lines working their way up the screen) seems similar to what would happen to his.. and it only happened on DBLNTSC/DBLPAL/other 31khz modes.  Why dropping the intensity down a bit helped, I don't know, but I think one of us read somewhere (Aminet probably) that this would fix it.