Hi Dave, welcome to the community.
Cracking first cab.
As has already been said, your cab's wired for JAMMA and has an adaptor for the Phoenix board (which is not JAMMA).
Here's a pic of where your volume pot should be. turn this gently to adjust the volume (you should be able to use your fingers, if not, a small screwdriver);
Phoenix is a 2-layer board, which means it has 2 PCBs. It looks from your pic that there is nothing to separate the 2 boards. I'd strongly recommend fitting some PCB spacers to create a gap between the boards (in the meantime, a piece of thick cardboard or anti-static bubble wrap will help). If the 2 boards touch, something could short and become damaged. Make sure you switch the cab off before moving the boards in their current condition.
I got a Phoenix board recently and it was in the cab just like yours (no spacers between the boards).
A couple of cheap spacers and feet later (OK, it's as tall as a double decker bus, now, but there's no chance of anything shorting);
I'm pretty sure the adaptor is made specifically for Phoenix, and will only work with that board (somebody may correct me). In which case, when you do get some new boards, just disconnect the adaptor from the JAMMA connector, and leave the adaptor on the Phoenix board when taking the board out. No point removing the adaptor from the board unless you need to.
Jay