No, close enough I reckon.
Had another thought, and this one is even better than the last one re ROM setting. Check the jumper section; if the machine is jumpered for overseas that may preclude the credit knocker from working. To set it up for US (standard) you need to ensure that W14 through W18 all have jumpers in place.
They are located on the CPU board, just below and slightly to the left of U9 (a large mostly square IC). The jumpers themselves are designated as 0 ohms resistors, that is, a link. If you have no spare jumpers available you may be able to get a way with a bent paper clip (any comments on whether this is OK?).
Can you post a picture of what a jumper looks like? 
I think I am way out of my league now, I think it might be better for the knocker to remain non-functional than it would be for me to start poking around in the backbox. I should be getting the new ROM version soon so I will see if that fixes the problem, hopefully it does.
Cheers,
Matthew
It may or may not fix the problem as the jumpers may override certain ROM settings.
I will see if my pins have jumpers and take a photo for you.
