If its not a bootleg than the 1st thing to check are the jumpers on the ROM board, as multiple games were released on the same PCB they used jumpers to select the relevant ROM sizes per game. Your fault may well be due to a missing jumpers.
If your ROM board has a large Sega custom on it (315-5250) then its the same board as mine so these are where jumpers need to be
S6 Yes
S5 No
S4 Yes
S3 No
S2 No
S1 Yes
S10 No
S9 Yes
S8 No
S7 Yes
S16 Yes
S15 No
S14 Yes
S13 No
S12 No
S11 Yes
Take a photo of your ROM board as it is now before you start pulling out any jumpers, in case you do need to revert for some reason. Sega released games on multiple ROM boards so the above may not suit your version.