While testing before the IOTA contest at G8X the K3S came up with the error "HI SIG" warning
From the manual:-
"An extremely strong, sustained signal (e.g., a broadcast station’s carrier) may be causing
excessive post-mixer amplifier current when operating on the present band. The K3 will automatically turn the preamp OFF, and in extreme cases will also turn the attenuator ON"
After disconnecting the antennas and turning the rig back on again the same error was displayed, and all controls were sluggish. At this point the K3 was used as a replacement and survived the whole contest without issue.
An Internet search suggested that the IF amplifier following the mixer consisting of Q8 and Q9 had now got shorted devices. Elecraft support were contacted and quickly responded confirming this theory. The devices used for Q8 qnd Q9 were discontinued, but some were found on EBAY. These took 24 hours to arrive and when fitted resolved the issue. The IF amplifier in the sub receiver had escaped unscathed. As a note Q8 and Q9 were easy to replace as you just have to remove the front half cover underneath the K3S, they are soldered to the underside of the motherboard
Elecraft support also mentioned that for a time the K3S was shipped with R66 in the IF amplifier as 10 ohm
"On K3S, make sure R66 is 15 ohm E500610 not 10ohm. We briefly shipped with it 10 and reverted back, **AND at the same time changed R60 & 75 so if R66 is 10 ohm, change it to 15 E500610 and R60 to 150 ohm E500251 and R75 6.2 ohm E500265"
My K3S was one of these radios so having replaced Q8 and Q9 and checked it worked, I changed the values of R60, 66 and 75.