How the lamp matrix drives a bulb

A TIP107 column driver switches +18 V onto the column, and a TIP102 row driver grounds the row; the bulb at their crossing lights. A 0.2 ohm sense resistor on each row feeds an LM339; if the row current pushes that voltage over about 1.4 V, the row is shut off to protect the driver until the CPU re-enables it.

Systems

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

Related tips

• How the WPC lamp matrix works
• How the WPC lamp matrix is switched
• No lamp matrix lamps light
• All matrix lamps stay on
• WPC lamp matrix and GI driver parts
• Lamp matrix fuse F114 (F106 on WPC-95) keeps blowing
• None of the controlled lamps work, or they light in the wrong pattern
• Testing lamp-row drivers with a test lamp

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