[Elecraft] Help: 20m died on K1 #1866

[hamblen9 at optonline.net]

Transmit on 20m abrubtly ended after weeks of being operational.. No output and minimal receive . Other 3 bands are operational with expected receive sensitivity and transmit output power. 20m receive sensitivity has always "seemed" inferior to other bands....I always assumed it was the antenna. 

Here's what I've done: 

1) I resolder all points on the filter board. All voltages on filter board are with in range. All resistances on filter board check with manual requirements. 
2) The transmit-mode DC voltages (pg. 46 manual) are all within range and the same as the original test measurements during the first alignment and tests. 
3) Confirmed b1-b4 band assignments were correct. 

Any help in steering me to where and what to do next would be appreciated. 

Thanks, Guy N7UN/2