Diode-test the lamp column and row transistors

Steps

• Game off, meter on diode test, transistor lettering facing you.
• Columns are TIP42s at the odd positions Q63 to Q77: black lead on the left leg (base); red on the centre leg or tab, then on the right leg: 0.4 to 0.6 each.
• Rows are 2N6122s (or TIP41) at the odd positions Q47 to Q61: test base (left leg) to centre (collector) and to right (emitter); expect 0.4 to 0.6 each.
• In-circuit results are about 95% reliable: a fail means bad, a pass is not proof.

Systems

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

Related tips

• Lamp matrix column test at 2J5 with Leon's code
• Test a TIP42 lamp column transistor with a meter
• Test each lamp column driver with a test lamp
• Light a lamp row by grounding its transistor
• Logic-probe the lamp columns and rows
• 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

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