Am 04.02.2011 18:33 schrieb Linards Ticmanis:
(...) RAM seems to suddenly fill with $FF for some reason (the screen will either fill with question marks "?"
The problem seems (note, *seems*) not to occur if the computer is just sitting at the BASIC prompt, but it does occur with different programs running
So it seems that the /WR signal remains active while the addres counter is incremented. Sitting at the BASIC prompt means ROM access and RAM read only. Starting up means write access to the memory area below $800.
In 99% of the cases it is a corroded IC contact. The best (but most boring) start is to lift each chip from its socket and push it back. You can work from both sides and tilt the chips by 15� instead of fully removing them.
Patrick