[1000mp] Sub RX dies on ONE BAND???

[Vic Culver]

Gentlemen, is it possible for the sub-receiver to 'die' on one band 
only in my FT-1000MP?  This morning while in the BS7 fray I could 
not hear ANY stations in the announced transmit band.  I couldn't 
hear anything on ANY PART of 20 meters with the dual RX (VFO A 
muted) on any mode.  I checked operation on 40, 30, and 18 meters 
and all was fine -- working normally as always.  But 20 meters 
remains dead!  I checked the Commander screens on the DXLab package 
and the set-up screens on the Microkeyer router -- everything seems 
as normal, except this one band doesn't produce audio on RX.

Has anyone experienced anything similar, and what might I check 
here?  Thanks for any comments or suggestions,  Vic, W4VIC