I've taken apart my fair share of Sega CD 2 and I happened to have one in pieces today to fix a sticky eject button when I noticed something I never saw in the last few Sega CD. Here's the picture I took:

One chip is 7474 , and another is 7404 hex inverter. There are 5 wires total: red and black are obviously +5v and ground and the other 3 I haven't identified. Any idea what this board is for? A Mod chip? A bug fix? I could try and rip the board off and trace the circuit on the bottom (it's held by a double sided foam tape)