Finding a short in a GI string

Steps

• Look for the usual causes: solder drips in sockets, metal debris in a socket, chafed wires touching ground, socket lugs touching other metal, a shorted socket or bulb.
• Game off: check either GI feed wire for continuity to ground (the two feeds connect through any fitted bulb). If grounded, follow the wire run for chafing or a lug touching metal.
• If not grounded, remove every bulb in the string and check each feed to ground and the two feeds to each other. Continuity between them now means a missed bulb or a shorted socket.
• If clean, reconnect and test bulbs; a shorted bulb won't blow the fuse or dim the string much.
• Disconnect one feed wire part way along the chain to narrow the short to a section.
• Shortcut: solder a lamp socket with a #44 or #47 bulb across the ends of a blown fuse and fit it in the fuse holder. With the string's bulbs out, the test bulb lights if a short remains; wiggle wires until it goes out.

Systems

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

Related tips

• GI will not dim or will not turn off
• One GI string is out
• One GI string dead with good fuses and connector

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