Testing the diode on a coil

Steps

• Turn the game off.
• Unsolder one lead of the diode from the coil lug, since the coil winding otherwise reads through the diode.
• Test the diode both ways on the diode range.
• Resolder it the right way round; if its lead is too short to reattach well, fit a new diode.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95
• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200
• Bally 6803
• Gottlieb System 1
• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B
• Gottlieb System 3
• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b
• Capcom

Related tips

• Testing a coil diode
• Which way a coil diode goes
• Which way a coil diode goes
• What the coil diode does and how a bad one shows up
• Coil diode and wire orientation when replacing a coil
• Coil-mounted diodes: replace rather than test
• Why WPC coil diodes are on the driver board
• Testing a coil diode on the driver board

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer