I have a Lewmar Concept windlass, capstan model, on my O'Day 37. It
has operated faultlessly until last Saturday. When attempting to
anchor on Saturday, hitting the Down switch produced a tiny
movement then nothing. After awhile, we got one more such
tiny movement. But no more. The solenoids in the control box
click away when the switches are activated but nothing
happens.

The 3-amp fuse is fine, otherwise the solenoids would not click. So is
the 100-amp circuit breaker

Voltage across the motor terminals, when the switch is on, is
13.33.

Voltage drop in the system is negligible. It's 13.5 at the
batteries.

Nothing is jammed. I have disassembled the above-deck unit
and only the spindle is now projecting above the deck plate.
Won't rotate.

I suspect an internal gearcase jam but have no idea how such a
thing could have happened. Would it help to tap the thing with
a hammer?

Any ideas?