|My "first" KX3 during its early days at KG9DW.|
I heard back from Elecraft yesterday, and my KX3 is officially toast. You see, it wasn't ever designed to have 120VAC applied to the external power connector. As I feared, the current transitioned through the control board, wiped out some components, traveled across the leads to the RF board, took out multiple components, and then exited through the well grounded antenna connection.
Talking through the options, fixing it is cost prohibitive. The guys at Elecraft are working on an option for me, so I'm hopeful I'll have a working KX3 back in the shack in the next couple of weeks. In the meantime, I've got a loaner radio from a buddy in the shack. It transmits fine but its receiver is so, so deaf compared to the KX3. It's like going from an iPad Air to a Palm Pilot.
In the comments of my last post about this mistake, the suggestion of fusing along with a diode was brought up. I'll definitely be putting more thought into my power supply cables after this costly error.