+5 V is low or missing.

No +5 V on a System 7 power supply

Cause: Bridge BR1, regulator chip IC1 (723PC) or pass transistor Q5 (2N6057).

Checks

• Test BR1 on diode test (its + lug points a different way from the others; - is diagonal to it).
• Check IC1 and Q5.

Fix

• Replace the failed part; replace Q5 with the easier to find 2N6059.

Systems

• Williams System 7

Related tips

• No or low +5 V from the power supply
• Early Black Knights use the System 6 power supply
• Power circuits in a System 3-7 game
• What the power supply board takes in and puts out
• Test the power supply with its outputs unplugged
• Sound aux supply keeps blowing its 2N6059: shorted capacitor on the 30 V rail
• Swapping power supply boards between generations
• Resets continue after diode repair: power and connector checks

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part One, Clay Harrell (pinrepair.com)