I was in the middle of the RSGB 80m club championship cw leg yesterday when the K3 suddenly displayed the above error message "ERR 12V". The KPA3 module (100w PA) went into bypass mode and the radio went into QRP mode and the fans came on at level 2. The power control would not adjust past 12W. I switched the K3 off and on again and it allowed me to set the power above 12w, however when I touched the key the K3 displayed the same error message and conditions.
I did a quick google search and came up with reports of this error message from many K3 users. One report suggested that it would be the pcb connection fingers between the RF board KPAIO3 board or between the KPAIO3 board and the KPA3 board (2 sets of connection fingers create a three board sandwich (RF board/KPAIO3 board/KPA3). The user suggested that a slight oxidisation of the pins can occur and cause high resistance on the 12V line. I took the top off, removed the KPA3, removed the KPAIO3 and examined all parts of the sandwich. I cleaned the pins and re-assembled the sandwich (as did the other user). To my surprise everything now behaves as normal.
When I think about it, this design is pretty flawed. You just have to look at the main pwr lead connections to RF board and then look at the poultry size of these connection fingers (2 connecting sets!) to the KPA3 PA unit which draws the highest current in the radio. What were they thinking about?
Hopefully this blog will help others when the inevitable happens.