Strange faults or lockups, worse after the game has been on 30-60 minutes.

Lockups and odd behaviour from a heat-dried C1

Cause: The +5 V pass transistor Q1 heats the whole aluminium "L" frame, drying out the C1 filter cap; Q1 itself can also fail.

Checks

• Check +5 V at CPU C16 after warm-up.

Fix

• Replace C1 with 6800-10,000 mfd, 20 V.
• If Q1 is bad, use a 2N6057 or 2N6059 for the hard-to-find original.

Systems

• Gottlieb System 1

Related tips

• Sound aux supply keeps blowing its 2N6059: shorted capacitor on the 30 V rail
• No or low +5 V from the power supply
• Resets continue after diode repair: power and connector checks
• No +5 V on a System 7 power supply
• Heat from Q1 cracks other solder joints
• System 1 power supply shows about 110 V where 4 V and 8 V belong: wrong ground
• Quick checks on the similar System 1 power supply
• Spare diodes, capacitors and other parts for System 1

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