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Internal DC and RF connector Confusion
1. We've had a couple of people mistakenly connect the KBT2 internal battery to RF AUX connector P6 instead of P3. This usually burns out the relay for which ever band the K2 was set to. The battery is capable of very large current flow, and the antenna input of the K2 is a DC short because of the 3&4 secondary winding of PA output transformer T4. (check your schematic to see why this is true) Whichever low-pass filter relay that is selected cannot withstand even a brief application of such a high current from the gel cell.
2. Also, if you accidentally connect the KAT2's internal antenna tuner RF input connector J7 to the Battery connector at P3, it may burn out the circuit board trace between the K2's DC input coaxial jack and P3. Depending on what your DC supply is capable of, a large amount of current can flow in the PC trace that goes from the K2's coaxial power connector to the Battery connector at P3. This is because the right terminal of Battery connector P3 is at +12V, and the right terminal of the atu's RF input connector J7 is at ground. Thus, a dead short can be placed across the K2's DC input jack if the atu's RF input connector is connected by mistake to the Battery connector. The power switch and self-resetting fuse is located *after* these points in the circuit, so there is no protection against such a costly and tragic error.
3. If you have both the atu and internal battery options, please tag or paint the white connectors with a color code that helps you identify and avoid making these mistakes that can cause extensive damage to your K2.
Thanks and 73.
Gary Surrency AB7MY
Elecraft Technical Support