The Zeiss Favorit 70 projector comes with a built-in rectifier for the optical soundhead. If your Zeiss projector inexplicably keeps blowing the mains fuses, this is where you should start looking for problems. Unless someone's bothered to rewire the rectifier or the power cables that provide it with 380 Volts, chances are that the latter no longer have any insulation left.
So look out for cable rot in your Zeiss projector.