[Elecraft] K2 #609 goes deaf ?

[JA Crux]

I noticed today that my very heavily-used K2 #609 has suddenly gone rather 
deaf. This seems to affect only certain bands, like 12m 15m and 17m, probably 
also 20m, but not 30m 40m or 80m as far as I can judge. Hard to tell when the 
bands are pretty dead here, but it was very noticeable on 12 and 15 when I 
was chasing a very weak signal from TJ3G. 

I know the problem is almost certain to be in the front end somewhere because 
if I use the preamp it brings up the background noise level, but not the 
signals. Comparison with the Omni-V confirms the deafness. The bands are much 
noisier on the Omni and virtually dead on the K2.  Also if I turn up the AF 
gain, the noise from the back end of the receiver seems to come up more than 
the the signals.  

Yes, it seems to transmit normally, with the usual power output on all bands I 
checked, so what did I manage to blow ??? And how ?? RF from the Omni does 
not hit the K2 and anyway it took a small (!) lightning hit in ZS6 in 2002 
without any damage. 

I am off to ZS again tomorrow, but the K2 will now stay home.  Any suggestions 
will be gratefully received. I just hope that I do not need to replace 
relays....  YUK.

John G3JAG