Testing driver transistors in diode mode (board out of game)

Steps

• Set the meter to diode test.
• TIP122/102: black probe on the centre leg or tab, red probe on each outer leg in turn; expect 0.4 to 0.6 V each.
• TIP36c: red probe on the centre leg or tab, black on each outer leg; expect 0.4 to 0.6 V.
• 2N4401 pre-driver (no tab): red probe on the centre leg, black on each outer leg; expect 0.4 to 0.6 V.
• TIP42 lamp column driver: red probe on the centre leg or tab, black on each outer leg; expect 0.4 to 0.6 V.
• Any other reading is a bad transistor; a shorted one usually reads zero or close to it.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• CPU and driver board transistors by position
• What the System 11 auxiliary power driver board does
• What the auxiliary power driver board holds
• When a driver fails, replace its pre-driver as well
• Lock diverter locks on at power-up and gets hot: shorted driver transistor Q22
• Quick check of all TIP122/102 drivers before first power-on
• Firing a coil or flasher from its TIP122/102 driver tab
• Coil fires when tested but not in game play: TTL driver chip

Source: Repairing Williams System 11 Pinball 1986 to 1990, Deel 1, Clay Harrell (pinrepair.com)