Probably something to do with C ROM access (bad trace or faulty IC).
Firstly thanks for the help,spent some time with the multimeter checking traces from the cart connectors they were fine, no gauged or broken traces.
Problem however is due to slight battery leakage, which has corroded two traces that go to the NE0 ZMC2 IC, two traces corroded battery not leaking badly but enough that these two are broken.
As the board was sold as working fine, im not repairing but shipping back to the seller for replacement pcb. Word of warning this was sold by halgames in Holland off ebay, slightly fucking annoyed as they not tested this before shipping.
Im having real shit luck buying mvs boards at the minute , all the ones I bought off this forum have worked perfectly so ill fuck ebay right off in future.
Gald to hear you got it figured out. Patching 2 traces shouldn't be too hard if you really want to hold onto the board.
Also, I believe I have an extra 2 slot board, that I know works, if you're interested. I'm located in the USA though, so shipping might be a little salty. Not sure, as I haven't shipped to the UK in a long time. Let me know!