[Elecraft] VFO Drifts during Transmit

[Ron D' Eau Claire]

>...I was having a CW QSO on 20 meters this
> afternoon. My VFO started drifting un commanded during transmit.
> Yes the RIT
> and XIT were off. I cycled the power on and off. The VFO was stable again.
> Then after about 10 minutes after cycling the power back on the
> VFO started
> drifting again during transmit. I can watch the numbers in the VFO display
> change as I transmit.
>
> Where do I start looking?
>
> K2 S/N 323
> Glenn WA7SPY

Hi, Glen:

There is a known problem with the optical encoder that Wayne recently found
a fix for. I had lived with it for nearly two years when they finally found
it, although I NEVER had the bad luck to have it happen twice in the same
day.

The symptoms were just as you describe, but the frequency only changed as I
keyed. It stopped changing when I stopped sending.

The problem was traced to a minor issue with the way the Optical Encoder is
used. If the encoder is sitting right on a transition point in the optical
disk, the cycling of power can cause the uP to think the knob is being
turned while the rig is keyed. It was caused by a design feature that cut
power to the encoder during transmit to reduce power consumption by a few
mA, but the cycling causes the circuits to mis-read the encoder each time
the K2 switches back to Rx mode when it is set right on a transition.

Wayne posted a fix via e-mail on the reflector some weeks ago. It is a minor
change that disables the power switching circuit so the encoder stays active
at all times. That seems to have fixed the problem.

The fix might be on the Elecraft web page (www.elecraft.com) under
"Builder's Resources". If not, and someone else doesn't have a copy to send
along, I'd drop Elecraft support a direct e-mail.

Ron AC7AC
K2 # 1289