Thanks - I'm going to swap the board into a working 432A I have to confirm that it isn't a component on the board before I go all medieval on the Coarse Zero pot.

Thanks - Glad you enjoyed it.

I would be happy to try and help but I don't really understand the question - Are you saying that your A1A1 Auto-Zero assembly burnt out and you are wondering if you should buy a replacement? You could probably repair it but I think these were a "factory" calibrated unit as, while the schematic has parts on it, the replaceable parts list only has it as a full assembly. I think you might be better off trying to find a cheap 432A without sensor and give just swapping out the A1A1 into your original unit.