Gil,
As suggested, check the wiring (encluding the antenna).
If you aren't seeing any output from the '430 (or the other
ones) I'd also check the feed line between radio and tuner
if you didn't enclude that with the 'wiring' above. If
everything seems to be making good contact outside of the
tuner, then it's time to look inside the tuner. Look for
any obvious broken connections, black or burned spots, etc.
Switch contacts are a likely place to find problems, so
give them a good look. If all else fails, you might 'wack'
it between the eyes just for the hell of it, sometimes it
helps.
Can you 'burn out' a tuner with 50 watts? Yes, just
depends on the tuner...
'Doc