How a WPC coil, flasher or lamp driver chain works

Every coil has power on it all the time; the driver transistor switches the coil's ground side to fire it. The chain on the driver board runs from a 74LS374 logic chip, to a small pre-driver transistor (2N5401/MPSD52 or 2N4403), to a TIP102, and on the strongest coils on to a TIP36c. A failure anywhere in that chain can lock a device on as soon as the game powers 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
• A coil or flasher energizes as soon as the game is turned on
• The four groups of WPC coil outputs
• CPU and driver board transistors by position
• Fliptronics flipper coil wired wrongly
• 20-second test for shorted coil driver transistors
• How Fliptronic flipper drive works
• Electronic spares worth keeping for System 11 boards

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