[Elecraft] K3S KPA3A No Power over 12W

[Michael Carter]

G'day, Mike,

You mention checking diodes D7 and D10.  On the KPA3A module, the relevant diodes in the T/R switch are D2 and D3 in the receive path, D5 and D6 in the transmit path.

The loss of receiver sensitivity when the POWER control is advanced above 12 W indicates that D2 or D3, or both, are damaged OR their switching control voltage on their cathodes via Q4 and the 7R control line is not pulling the cathodes low on receive.

The inability to develop transmit power above 12 W indicates a problem with the diodes D5 or D6, or both, OR their cathodes are not being pulled low by Q6.

In the past others have found the T/R diodes closest to the antenna, i.e. D2 and D5, are more susceptible to transient overvoltage on the antenna port due to nearby lightning strokes and static build-up and discharge on the antenna due to wind and precipitation.

I suggest you check D2 and D5 on the KPA3A module first, then check the other two diodes of the T/R switch.

73,
Mike, K8CN