After a flipper rebuild with new coils, one flipper is weak and flickers; when the parts were swapped the fault moved to the other side.

Flipper weak after a rebuild: EOS opening at the start of the stroke

Cause: The end-of-stroke switch (normally closed) was opening early in the stroke, cutting the power winding out too soon. A pair of EOS wires had also been swapped during reassembly.

Checks

• Hold the flipper up and check the EOS is open by only about 1/8 inch; at rest it must be firmly closed.
• Compare the wiring with photos taken before the teardown.

Fix

• Re-gap the EOS so it stays closed until the very end of the stroke, and correct the wiring.

Systems

• Williams System 6 / 6A

Games

• Disco Fever

Related tips

• Most flipper faults are EOS switch faults
• Second-generation flipper rebuild: the right small parts
• Right flipper too weak for the top lock after a rebuild: lighter return spring
• Measure a flipper coil
• Fire a flipper coil by grounding it
• System 3-7 flipper coils are series wound
• Fitting parallel-wound flipper coils
• Weak flippers

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