In the all-lamps test one row or column lights twice per sweep (on twice as long), or in the single-lamp test two lamps flash together.

Lamps light twice in the all-lamps sweep, or two lamps act as one

Cause: A shorted or reversed lamp diode, a bad TIP107 or TIP102, or a short between two matrix wires on the playfield, often a solder drip from coil work landing on a lamp board header.

Checks

• Note every lamp that double-lights and find its row and column in the manual; look for a shared row or column.
• Test the related TIP107 and TIP102.
• Unplug the lamp matrix plugs from the driver board and, on the harness plugs (not the board), check the row and column wires for zero ohms to each other.

Fix

• Replace the bad transistor, or find and clear the short or replace the shorted diode on the playfield.

Systems

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

Related tips

• An entire lamp row or column is out
• A lamp column or row stays on all the time
• A lamp row very bright or dead
• A whole lamp row or column is stuck very bright
• Testing lamp-row drivers with a test lamp
• Testing lamp-column drivers with a test lamp
• No lamp matrix lamps light
• A row or column of lamps stuck on and too bright

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