Testing a coil diode on the driver board

Steps

• Find the diode tied to the coil's driver transistor leg on the schematic; it sits next to the transistor.
• Meter on diode test: black lead on the banded end, red on the other end should read 0.4-0.6.
• Swap the leads: there should be no reading.
• If the readings are wrong, clip one leg loose and test again; if still wrong, replace it with a 1N4004.

Systems

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

Related tips

• Why WPC coil diodes are on the driver board
• Testing lamp-row drivers with a test lamp
• Testing lamp-column drivers with a test lamp
• Testing a coil diode
• Testing the diode on a coil
• Which way a coil diode goes
• Which way a coil diode goes
• Testing coil diodes on the auxiliary power driver board

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