Convert a -133 MPU to a -35

Steps

• Find CR52 (the R113 position) at the lower left of the MPU next to J4.
• Remove the 1N4148 diode and fit a 2K 1/4 W resistor.
• Re-jumper the ROM area if the ROMs will change; Baby Pac-Man usually shipped with a 2732 at U2 and a 2532 at U6 (page 14).

Systems

• Bally MPU AS-2518-35

Related tips

• Converting a -133 MPU to a -35
• Telling a -133 MPU from a -35 or -17
• -17, -35 and -133 MPU boards compared
• Tell a -35/-133 MPU from a -17 by counting J5 pins
• Jumpers for a -35/-133 MPU running two 2732 EPROMs (U2 and U6)
• What changed on the -133 MPU: zero-cross sensing from 6.3 V AC
• Testing an MPU in the game with only J4 connected
• Bench-testing a -133 MPU: swap the R113 diode for a resistor

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