Because the KAT3A was marketed both as a replacement for the KAT3 and as a component of new K3s rigs, its installation instructions show how to remove the previous antenna tuner card, if necessary. Please consult the first 10 pages of https://ftp.elecraft.com/K3S/Manuals%20Downloads/E740266%20KAT3A%20Option%20Installation%20Rev%20A1.pdf 73, Paul W8TM