Yes I have to agree with you there Richard, aren't they quartz anyway now? Large motors changing polarity or AC single phase to three phase on delta variants I have always carried out especially in the old days and when uprating the charging system on cars from positive earth to negative earth. Flashing clocks though does seem to be a well used reported method. Think I might go and have a rummage about in the parts bin and strip an old smiths clock and see what I can find or perhaps make it do!
Little more research, if you have the electro/mechanical later type it has two coils moving between the poles of a magnet. As the coils of the balance wheel move between the poles of the magnet a transistor was switched on providing a pulse to the coils to drive the balance assembly and thus the hands of the clock through a gear train. Perhaps it could be that the transistor has failed thus altering the switching polarity. Richard's knowledge needed here.
