Knut Roll-Lund wrote:
Grasping at straws: What if there is an adressing problem that data is
overwritten because of an adress line failure. Would APTEST see that? Is
there a RAM test that would test the address lines?
I don't think APTEST would see this at all. The RAM test in APTEST is
extremely simple minded: fill all of RAM with Value X, then test if it's
still there. Repeat for next X. This obviously won't find broken or
flaky address lines.
You could try something simple like this (with no DOS loaded):
10 FOR I = 2500 TO 49000 STEP 2
20 PRINT I;
30 POKE I, 85:POKE I+1, 170
40 NEXT I
50 FOR I = 2500 to 49000 STEP 2
60 PRINT I;
70 POKE I, 170:POKE I+1, 85
80 NEXT I
Then see if and at what value of I you get screen corruption.