Masked ROM numbers: keep the set matched

A higher dash number on a masked ROM is a later revision. The U6 revision matters because a game usually will not run with the wrong U6. U1 and U2 revisions belong to versions of the same game, and every chip in the set must be from the same version; old and new cannot be mixed.

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35

Related tips

• 9332 masked ROMs can be replaced by 2532 EPROMs as-is
• Old black masked ROMs fail from tarnished legs
• Why the MPU has ROM jumpers
• How the first-flash ROM test works
• After the test EPROM: refit the game ROM and count flashes
• ROM and EPROM types used on Bally MPUs
• Get the MPU booting before you change any ROM jumpers
• Bally -35 MPU jumper settings by ROM type

Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Two, Clay Harrell (pinrepair.com)