Sega Genesis Model 1 Cyclical Reset/Reboot

I've run across an odd Sega Genesis. It will power on and boot a game, but it will keep "resetting" the game about 2 or 3 seconds in. For example, you know that "Sega" fanfare at the beginning of Sonic 2? It will just keep playing through that over and over. I'm using a known good AC adapter (works well with another Model 1, 9v 2A output so it puts out plenty of juice), I checked the internal 5v supplies (solid 5.02 volts). Any ideas what to check or what could be wrong? Thanks.

p.s. if you need to see a video, just ask and I'll try to get one posted.