I know,when I got the mega drive there was a mod already done on it,it worked but was playing in 50hz in black in white because of the 53.203Mhz oscillator. What I did was remove the region jumper mod and installed a 53.6931Mhz oscillator and it played in color and at 60hz.
You are in america, PAL/50hz is never going to work well there. Changing the jumper would give you PAL/60 - again, not going to work well in the states. You could have gone RGB, but that requires a RGB tv. But the OP is in the UK, so RGB all the way id imagine.
