A bit of a lessons learned here I'm afraid.
Took the K2 apart looking for the deaf 10m problem. The symptoms were:
10m tx fine
10m rx deaf
12m tx fine
12m rx fine
A really puzzling set of symptoms because 10 and 12m share the same BPF and LPF. The only difference being the addition of 2 capacitors to the BPF by relay when the 12m band was selected. I hunted around these areas looking for solder splashes that would keep these caps connected when 10m was selected but found nothing.
In desperation I tried injecting signals direct from the antenna though a 480pf cap to various points before and after the LPF/BPF. When connecting to the start of the BPF the rx sprang to life...haha I thought it's the LPF! But even when connecting to the very last component of the LPF the rx was deaf. I followed the circuit diagram and noticed that the signal path went through the 160m optional module. On connection before the 160m module the rx was deaf. On connection after the 160m module the rx sprang to life. What on earth was happening on the 160m optional module that was causing 10m rx to be deaf? Then it dawned on me, the 160m optional module allows a separate rx antenna to be used on ANY band. A quick look in RANT menu selection confirmed that 10m was selected to use the rx antenna! A quick couple of key presses and hey presto all was well.
Ok, it would be nice if the firmware let you know that the rx antenna was selected for that band by showing some symbol on the LCD but I really shouldn't have left it in that condition in the first place. I had been fooling around with a 2m transverter with a 10m IF and had left the rx ant option selected on the 10m band...easy to do I suppose.
Anyway the long and the short of it is that the K2 is 100% healthy and ready for IOTA :-).