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Pre-show testing found the game not booting and a display full of 1s. Attaching the Arduino ICT and running "RAM Check All" reported "E: 7P 4000 01 09" and testing through all the individual RAMs with ICT didn't find any other failures except for IC 7P (2114). Replacing IC 7P (2114) fixed the RAM test failure and the game ran OK on the bench.
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In the cabinet the game would coin up or reset during game play when joystick right was used. Checking the input pull-up voltages at the joystick confirmed they were all OK (TTL high) and the game PCB was removed for repair. Testing on the bench didn't find any issue during game play. Checking IC 8N (LS138) chip select outputs all looked OK on the scope. Activating player 1 down, not used on original Galaxian, reset the game. Player 1 up caused a coin-up. Checking the multi-game documentation confirmed that the original Galaxian TEST & SERVICE pins were used for the additional down & up inputs needed for some games. This was a simple case of accidental up or down during game play activating those inputs on original Galaxian. A modification was made to the Midway Galaxian PCB to lift a couple of resistors and strap them high to disconnect and tie off the unused inputs. Testing in the cabinet confirmed the issue was fixed.