Greetings Jim!
I have had the same problem with my DX-390. I can't remember which
transistor it was on the board. I might open it up and see if I can
remember.
Conditions were bad Sunday. I heard almost nothing at all on 75 meters
on my FT-980.
One more thing to try on the DX-390. Attach an external antenna via the
antenna connection plug on the left side. One time mine would not
receive squat via the whip, but connected to an externa antenna via the
antenna connection on the left side it came right to life. That time
the whip antenna had somehow broken it's connection with the board.
Good luck and have a great week! Jon.