How the control board reset circuit works

At power-on a 10 uF capacitor charges through a 5.6k resistor; at about 2.7 V a 2N4400 turns on, which turns on an MPS-A70, which turns on a second 2N4400 that latches the circuit and releases reset. A 1N4148 empties the capacitor so a quick off-on still resets. A separate power-down detector (Q1 and one-shot Z1) pulses reset if the 5 V sags.

Systems

• Gottlieb System 80
• Gottlieb System 80A

Related tips

• Reset section zener VR1 burnt on a System 80 CPU board
• Game check-out, part 2: what a healthy power-up looks like
• Scores light at once and the status display stays dark
• Bookkeeping totals or score levels are wrong or missing
• Random game over, lost credits or erratic features
• System 80 control board chips
• How the control board drives the displays
• Control board power-on checks

Source: System 80 Service Manual, Gottlieb