i have a TT that works ok except that as soon as it get's to desktop random dots and vertical / horizontal lines appear (typically more when the machine is not idle / ie: floppy drive seeking)
i have checked all i can think and changed the TT video chip
did think possibly memory but the marpet memory test says ok
also when used with the TT test cart it get's no further than this message "looking for FPU"
yes the FPU is installed and yes it works fine as i tested it in another machine
so could possibly be related?
if you look close at the pic below you can just see small line/dots in the white area, hard to take a pic of the actual bars as it is so random!