[Elecraft] Sudden K3 failure

[Mpridesti]

Yesterday while just listening to a SSB QSO, the receiver just went quiet and when I tried to transmit, got nothing. 

Power setting was at 75 watts and varied properly but meter and external output monitor was showing nothing. 

Thought the filters stopped passing RF. 

Rechecked the filter settings on the Utility program and all seemed normal (no change).  

What could cause the radio to behave like this? During receive?

Regards,

Mark, K1RX