Replacing the MPU reset section with a DS1811

Steps

• Fit a new 82 ohm 2 W resistor at R11.
• Take out Q1, Q5, VR1, R1, R2, R3, R112, R138, R139 and R140. CR5 and CR7 stay.
• Run a wire link from the R138 hole that is lower (as the board hangs in the game) to the R139 hole that is higher.
• Mount the DS1811 with its flat side toward J4. Its bottom pin (reset) goes to the Q5 collector hole, the single left-most Q5 hole nearest J4.
• Add a 1k pull-up resistor from +5 V to the DS1811 reset pin (the banded end of CR5 is a handy +5 V point).
• Connect the DS1811 middle pin (VCC) to the bottom-right Q5 hole (+5 V) and its top pin (ground) to the top-right Q5 hole.
• Power up; the opening flicker will last longer because the reset time grows from about 50 ms to 150 ms.

Systems

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

Related tips

• Game reboots at random: R11 heating Q5
• Replace a discoloured or carbon R11 on the MPU
• MPU U9 voltages that show a working reset section
• Replace the System 80 reset circuit with a DS1811 chip
• Testing the MPU reset circuit at U9 pin 40
• Resets from a bad MPU J4 power connector
• MPU reset section parts by position
• Quick test of reset transistor Q1

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