After rebuilding the pop bumpers with new lamp sockets, the upper general illumination fuse blows, even with the bulbs removed.

Upper GI fuse blows after a pop bumper rebuild: solder blob inside a new socket

Cause: A short in one of the new pop bumper lamp sockets: a stray piece of solder inside the socket bridged it. GI is AC, so socket lead polarity does not matter.

Checks

• Remove the pop bumper bulbs: if the fuse still blows, the short is in the wiring or sockets, not the lamps.
• With power off, check each new socket for continuity between its two leads and from each lead to the mounting bracket or pop bumper frame.
• Look inside each socket for solder splashes or pinched wires from the rebuild.

Fix

• Clean out or replace the shorted socket and recheck the rest of the rebuild work, then fit a new fuse of the correct rating.

Systems

• WPC Fliptronics

Games

• Fish Tales

Related tips

• One GI string is out
• Lamp matrix fuse F114 (F106 on WPC-95) keeps blowing
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• Pop bumper and target GI lamps dead: a previous owner's added socket shorting
• Some tachometer (RPM) lamps won't light: failed lamp diodes
• No GI at all
• General illumination strings

Source: Pinball Repair help group!! (Facebook group)