Is there any chance that someone connected the red and black power wires backwards?
The brown schmoo is most likely the brown kraft paper that used to be on the inside an electrolytic capacitor. Reverse polarity is a popular way to explode this kind of component like we see in the pic.
If the power is down, it's most likely that you have one or two damaged RF power transistors. Have a very close look at the input side of those transistors. A resistor that looks burned or darkened attached to that end of a RF transistor indicates a bad one.
The SD1446 was discontinued over ten years ago, and not so easy to find. Good chance you'll have to replace both, if only to make sure they both match reasonable well. Even if only one of them is blown, you'll have a hard time finding a new single part that properly matches the 'good' old transistor.
73
