ps2 modchip

Hey guys. I bought a PS2 Slim 70004. On the case it says it is 75004 :)). I have a problem with FMCB, OPL and so on because sometimes they dont run. I tried to check if it is hardmodded and it is, but i can't identify what modchip it is and how to use/enable/disable it. If you guys could help me...