you sure its the right ac adapter and you didn't reverse polarity and fry stuff??
ive had RF issues before as well.
unfortunately since there is no power indicator you can't tell if its properly turning on....
As dumb as this sounds, try plugging the RF directly to the TV. No other connections to the TV, just the PC Engine, and power it on.
My one Turbo grafx for whatever reason, would not work unless it was the only thing plugged in. If I plugged the cable from the wall for cable TV, the picture would go out...