Do not mix up the two pop bumper switches

An early System 11 pop bumper has two switches: the one under the skirt fires the coil directly, and a second one only scores and makes sound through the matrix. If a bumper has a single switch with a diode on it, the processor fires it; that switch is a matrix switch, so test it in the switch test and do not ground it.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Pop bumper bracket with a loose coil stop can be saved by re-peening it
• Pop bumper switch cup lubrication
• Fuse blows, pops and slings dead: slingshot switch stuck shut cooked coil and Q11
• One pop bumper weak and sluggish though coil and switches are fine: replace Q77
• Pop bumper or slingshot machine-guns or locks on (Fire! and earlier)
• Later System 11 slings and bumpers are processor fired
• Special solenoids dead after fitting an early System 11 CPU in a later game
• The six special solenoids (pops, slings, kickbacks)

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer