If you have to power the game off and on then the problem is fixed by resetting the CPU board. I think that you may have an issue with ROM / RAM or CPU socketed ICs. See if the game locks up / freezes when you lightly push socketed ICs on the CPU board, or jiggle the connectors on the CPU board. Is there any corrosion on the CPU board ? Check the bottom LHS connector.

When the game freezes - check the voltages at the CPU board (+5V and +12V Test points) - If they are good, then it will be the CPU board. Is is an original or after market ?