Testing lamp-column drivers with a test lamp

Steps

• Backglass off, display lowered, game on in the All Lamps test.
• Unplug J133 and J137 (J124 and J121 on WPC-95).
• Clip a lead from row connector pin 1 (rightmost) to one terminal of a working 555 socket.
• Clip a second lead to the socket's other terminal with a 1N4004 held in its far end, banded end facing out.
• Touch the diode's banded end to each pin of the column connector header; the lamp should flash on each.
• A column with no light or a steady bright lamp points to its TIP107 (or a reversed diode).

Systems

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

Related tips

• Test each lamp column driver with a test lamp
• Testing a coil diode on the driver board
• Why WPC coil diodes are on the driver board
• Testing a lamp diode
• "Check Fuse F114/F115" (F106/F101 on WPC-95): step-by-step
• Getaway: beacon runs nonstop in test and driver board C11 overheats
• +20 V filter capacitor C11 (C10 on WPC-95) blows apart
• Why diodes on 555 lamp boards crack

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