Test a TIP42 lamp column transistor with a meter

Steps

• Meter on diode test, lettering facing you.
• Black lead on the left leg (base).
• Red lead on the centre leg (or tab): expect about 0.4 to 0.6 V.
• Red lead on the remaining outer leg: expect about 0.4 to 0.6 V.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Diode-test the lamp column and row transistors
• Lamp matrix column test at 2J5 with Leon's code
• Replace the TIP42 lamp column transistors with IRF9Z34N MOSFETs
• Test each lamp column driver with a test lamp
• Lamp and switch matrix transistor positions on the CPU board
• A column of controlled lamps out: failed lamp column transistor Q60
• Lamps in two columns light together in single lamp test: failed lamp column transistor
• CPU and driver board transistors by position

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