20-second test for shorted coil driver transistors

Steps

• Game off.
• Meter on ohms or continuity.
• One probe on the backbox ground strap.
• Touch the other probe to the metal tab of each TIP102.
• A beep (0 ohms) means that transistor is shorted on. Replace it, and its pre-driver, before powering up.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Where the WPC coil and lamp drivers sit
• How a WPC coil, flasher or lamp driver chain works
• Which transistor drives which WPC solenoid and lamp circuits
• Supercharger diverter dead even in test: open TIP102 at Q81 that tested good
• A coil or flasher energizes as soon as the game is turned on
• WPC lamp matrix and GI driver parts
• The four groups of WPC coil outputs
• How the WPC lamp matrix is switched

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)