[Elecraft] I Went and Did it Now?

[Ron D'Eau Claire]

> I guess I really screwed up. I was getting my K2 (trusty #023) ready for
FD.
> I was hooking up my old laptop, to send CW with TR log. Something
happenned,
> and I got on the outside of the serial connector. Nor this didn't go to
the
> KIO2, but to my interface, with a transistor to ket the K2 in CW. I key
> through the mike jack PTT line...
> Anyway, the voltage difference has blown something in the K2. When I turn
it
> on, it is stuck on transmit. It appears something on the control board is
> blown.
>
> I have it apart, but not sure where to start. Nothing appears fried. I
tried
> tracing the "PTT/DOT" line on the schematic and just got a headache ;-)
>
> Anybody "been there, done that?"

I'm happy to say that I haven't been there nor have I done that, but I took
a look at the schematic diagram. The /DOT PTT and /DASH lines go to the
Control Board where they are held at a "high" by two 82 k resistors in RP4.
They are at the right end on the connector on the schematic. The /DOT PTT
and /DASH lines go straight to the MCU, U6 at the RD6 and RD7 inputs.

My guess is that you "fried" the MCU with the voltage. Your interface
probably pumped significantly more voltage into the key lines than the
normal bias provided by 5A. Normally, I'd use a simple transistor switch to
ground to key the rig electronically, with the collectors only receiving
what voltage is provided by 5A through those 82 k ohm resistors.

Ron AC7AC
K2 # 1289