[Article 6316]Troubleshooting Asteroids PCB (4)

Problem solved.

After checking  (as suggested in the VECTORLIST) the Vector Timer Circuit, with a particular attention to 74LS83 ( four-bit adder) at location M, I expanded my research to all the data flow from the ROMs to the XY Position counters. Everything seemed to be ok but paying attention to the scope I could see signal LOAD6  was different from other LOAD* signals. Replacing 74367 at locatio H6 the problem was solved.