Driver transistors Q1-Q4: relays and spare outputs

All MPS-U45. Q2 (far left) drives the Tilt (T) relay from CPU Z26 pin 3/4 via A1J5-5 and driver Z1 pins 5/7. Q1 drives the Game Over (Q) relay via Z26 1/2, J5-6, Z1 4/2. Q3 (lamp L3, often High Game to Date) uses Z26 5/6, J5-4, Z1 12/10, and Q4 (L4, often Shoot Again) uses Z26 9/8, J5-3, Z1 13/15; either can instead pre-drive an under-playfield 2N5875.

Systems

• Gottlieb System 1

Related tips

• Spare transistors for System 1 boards
• Testing MPS-A13 and MPS-U45 driver transistors
• Testing the 2N6043 coil drivers
• How many coils the driver board can fire
• Meter transistor tests are not conclusive
• Diode test of driver board 74175 chips
• Early driver boards lack isolation diodes
• Testing the Q45 2N3055 and its resistor

Source: Gottlieb System 1 Pinball Repair from 1977 to 1980, Clay Harrell (pinrepair.com)