I had about the same problem with an asteroids board (even the selftest was
perfectly okay)! It would draw a lot of recognisable objects, in a unorderly
way and would start over again (not because of a watchdog reset). It turned
out to be an LS04 inverter in the State Machine. If something goes wrong in
the state Machine or the Program Counter, these things will likely to be
happen. You should check all TTL chips in that area, simply look for a nice
output on all gates by using a o'scope. The LS04 that cause my problem only
changed the output between VCC and 2.5V, in stead of 0 volt.
Good luck!
Mendel
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Received on Wed Jul 2 16:31:18 2003
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