Combining two-chip CPU code into one 27512 for 5C

Steps

• Get the game's 5B and 5C code images.
• If 5B and 5C are both 27256 images, join them as one binary file with the 5B image first and the 5C image after it (for example with a binary copy command).
• If 5B is a 27128 image, put the 5B image in twice, then the 5C image, so the result fills a 27512.
• Burn the 64 KB result into a 27512, fit it at 5C with 5B empty, and set J4 out, J5 in.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3

Games

• Back to the Future
• Batman
• Checkpoint
• Laser War
• Monday Night Football
• Phantom of the Opera
• Playboy 35th Anniversary
• Robocop
• Secret Service
• Teenage Mutant Ninja Turtles
• The Simpsons
• Time Machine
• Torpedo Alley

Related tips

• Wrong speech and sounds play for callouts: battery-corroded CPU board
• Free play and high scores act as if memory resets every game: do a factory reset
• Test EPROM flash codes: which chip failed
• Where the main chips sit near the CPU board batteries
• Other CPU jumpers and what they set
• Bench-testing a CPU board on +5 V
• CPU boards are only downward compatible
• CPU EPROM jumpers J4 and J5

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Two, Clay Harrell (pinrepair.com)