Each memory drop target coil works alone in test, but when the outhole coil fires, memory coil 1 fires too, and when a drop bank resets, memory coil 2 fires as well.

LE: one coil fires another (outhole fires a memory coil): coil diodes

Cause: The coils switched through the solenoid expander share drivers, so each needs two isolating diodes. A failed diode on one of them (here on a seven-bank reset coil), or a replacement coil fitted with only one diode, lets the current find a path through the wrong coil.

Checks

• Check every coil on the expander circuit has both diodes fitted, and test each diode with one leg lifted; a diode can read good in circuit.
• In lamp test, listen to the expander relay: a buzz instead of a clean click points to a weak 7 V supply bridge.
• Make sure the incandescent bulb next to the expander is fitted and working; it loads the circuit so the expander switches properly.

Fix

• Replace the bad coil diode(s), adding the second diode where a single-diode coil was fitted.

Systems

• Bally MPU AS-2518-35

Games

• Eight Ball Deluxe (LE)

Related tips

• Expander-driven coils fire in pairs: drop target coil fitted without its second diode
• One pop bumper scores but never fires: broken wire hidden under shrink tubing at the coil
• Drop target coil won't fire in test: replace its diode
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• Drop target falls instead of the ball being kicked out (SEB games)
• Drop target coil fuse keeps blowing: shorted diode on the coil
• Coil diode and wire orientation when replacing a coil
• No playfield coils work

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