Upsize the sand resistors on -18 regulator boards

R1 (600 ohm 10 W) and R2 (25 ohm 10 W) on -18 style rectifier boards often burn, especially in Stern games. Replace R1 with 620 ohm 15 W (about 30 degrees cooler) and R2 with 27 ohm 10 W (about 20 degrees cooler).

Systems

• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200

Related tips

• Route of the +12 V supply to the MPU and 5 V regulator
• Logic 5 V reads over 5.25 V on Bally/Stern: the R49 boost resistor

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