Use a 7437 or 74S37 at MPU U15, never a 7400

U15 originally held an MC3459, now discontinued. It has to sink about 30 mA: a 7437 sinks 48 mA and a 74S37 60 mA, so either is fine. A 74LS37 (24 mA) is only an emergency fill-in, and a 7400 or 74LS00 (about 4 mA) will not work.

Systems

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

Related tips

• MPU LED never lights at all
• Testing an MPU in the game with only J4 connected
• MPU board test points
• MPU board test point voltages
• New replacement MPU boards exist
• Why the MPU has ROM jumpers
• Telling a -133 MPU from a -35 or -17
• Converting a -133 MPU to a -35

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