Got a Cabal game. It looks like a bootleg but is pretty good quality. The ROM’s match that of the joystick version which is good because it means I can test it properly.
As it turned out, the joystick controls were completely erratic and all over the place. I took the top board off to give me access to the traces from the edge connector.
There is a small daughter board present which is silkscreened with “Joystic Sub”. I removed this and found the likely cause of the problem, several of the pins had broken off.
I cut the pins out that were broken and replaced them as required. Pins 13 and 14 were not connected to anything so I didn’t bother replacing them.
Fired the game up and the controls are working again. Pretty addictive game too.