Just a quick update on progress with repairs - thanks to Dave Hill's excellent photographs, I have gathered some more clues concerning the operation of the unit (even though his was a later model with more relays inside!).
It seems that the play switch had been replaced in my machine, and was of the wrong type (should have been a push to make, single pole switch).
The only problems I have now are:
A. The unit does not pay out on winning numbers, and
B. Both of the overload cutouts have burned out (they appear to have a thermal coil arrangement, wound around a thermally sensitive metal strip, which breaks contact when the coil heats up through excess current flow) see attached photo. They cannot be replaced by modern circuit breakers, because they have a three terminal arrangement.
I suspect that the non-payout problem is connected to these faulty cutouts. Is there a possibility that someone could measure the resistance of a cutout coil in their machine, so that I can wind some new coils from ni-chrome wire? Even better, if anyone has two complete cutouts they can sell me, I will gladly purchase them.
I also notice that the bell is missing from my machine - presumably this rang when a winning number came up?
Any assistance will be received with grateful thanks!