[Elecraft] Only one audio channel

[James Meade]

My K3 delivers only the left channel when listening with Heil stereo  
headset or an aviation stereo headset.  The Heil I tried from the front  
and back plugs, the aviation from the front only.  I have the sub  
receiver.  I usually use the radio with the speaker and only now found out  
one channel is out.  I don't know how long it's been that way.  I have not  
been fooling around with it.
RF gains is full CW for both main and sub.   AF gain as desired, tried at  
full volume.
It won't work split or sub.  I've checked every item in the Menu and  
Config settings per the Dec 7 2010 manual and the radio.  All appear to be  
right.
Any tips, please advise.
Jim NO0B