After finding that the output from the RF board to the amplifier board was nowhere close to the proper amplitude, I focused my attention on the RF board. I checked and rechecked the board, but couldn't see anything obviously wrong with the connections or with the board itself. By chance, I found someone selling the same board at a very reasonable price, so I bought it and installed it in my radio. Now everything works as it should.
As an exercise I may look over the old RF board more carefully, but now that the radio is working I'm certainly not going to board swap to troubleshoot the old board. If I find anything of interest on the failed board, I'll be sure to post to the group, but otherwise I consider this a successful conclusion to my repair adventures.
Thanks to everyone for all of their help and encouragement!
Stan N6BYU
