Mpu5 error help ?

Firstly my name's Chris this is my first post asking for help , I've been using this forum for my troubles with fruit machines for a while now and I can usually find my answer easily as there's alot of knowlagable fruity lovers here :-) however this problem I cannot wrap my head around..

I have a mpu5 machine that's been giving me issues for a few weeks now. I got it in a non working condition, it gave a battery low/dead error code so I replaced the coin battery and the machine powered up for about 5 minutes and gave a corrupt error aswell as a no I'd card error and character error, so I cleared the mem etc and it worked again for 5 mins and the same result... then nothing , it won't power the game card up at all, I replaced the green battery and then that also worked for a few minutes and it died again, every time I remove and test or replace and test the green battery it works fine for a few mins ... I don't understand what's wrong ? Any ideas at this point would be appreciated ...
I should also add I've tried another game board in this machine and it booted perfectly so the main board is fine I just don't understand how it will boot whenever it likes...