basically i was doing the composite mod to my megadrive and i had my laptop power adapter on the floor next to the md adapter and i plugged the laptop adapter in instead of the md . the laptop adapter is 19v and 4a. i turned the md on and after nothing onscreen for about 10 sec i heard a pop i have gone around the mobo with a multimeter but can't find the problem component. what would be a good place to start and what could have made the "pop'. both voltage regulators are getting extremely hot so i am assuming they are functioning but i have no idea.

Extremely hot regs means most likely they are fried. Standard rule of electronics: the hot part is either the part that failed or one part in the power path after what failed... nothing is before that in the power path. Hook the normal power adapter to it and check their output voltages. This is something which would really help to have a decent O'scope to diagnose.

The one on the left is putting out 1.69 and the one on the right is at 4.65. what are the normal voltages for the regs?

I am not a sega tech... you would have to find out the same way I would, via google research.