[Leica] Winder M problems

["Paul Bolam" <Paul@bolam67.freeserve.co.uk>]

I've just bought a secondhand winder M and found that it locks up the M6
0.85 mid-roll. At this stage, the film is wound on, the meter is switched on
but the shutter release won't budge. The rapid wind lever is immovable (due
to the film being wound on and the shutter cocked).

This lock up occurs after varying number of shots have been taken. The first
time it happened on the 25th frame and the next time after the sixth.

Switching the winder off and then back on has no effect and even when the
winder is removed the camera is still jammed! Eventually, the M6 resets
itself but I can't see how or what caused it to un-jam. However, the M6 will
not reset if the winder is in place.

Anyone got any ideas what's wrong? I put a fresh set of batteries in the
winder. Is it something I'm doing or is the winder dodgy?

Thanks in advance,
Paul.