No problem Terry, I am assuming you gently prised coil out of housing and
found tacho magnet on a plastic thread had worked loose?. I usually use a
spot of threadlock on shaft and tighten with a pair of needle nosed pliers
(bent nose type are especially useful here) then refit coil. (coil should be
held in place with a large castellated washer, usually black in colour)
you'll probably find castellated washer lurking in base of machine
somewhere.

The normal course of events is that the magnet comes loose and pushes coil
from housing, causing an overspeed on motor. PCB will sense lack of voltage
from tacho coil and go into a fault condition mode and avance to end of
cycle to prevent damage to machine.

If you cant find washer, drill a wee hole through aluminium housing and
secure with self tapper. (careful not to damage coil!!!)
But make sure magnet is good and tight first.

HTH

Egbert