Sam,
The most likely problem is a shorted input on the MCU.
As another has pointed out, a leaky C2 could also cause that problem,
but is not the most probable.
The MENU button may not be a problem - if the MCU is busy keying, it
will not respond to button taps.
73,
Don W3FPR
On 5/31/2026 10:33 AM, Sam Smith via Elecraft wrote:
Mike, thanks for taking the time to respond. I have done lots more tests and
narrowed things down.
First off, the K2 is on the bench with a dummy load and power turned down to as
low as it will go, so RF is not a problem.
The /DASH line on pin 29 of the MCU is "floating" around 2 volts. I am guessing
it should be 5 volts like the /DOT-PTT without keying it. That is what the voltage chart
says.
Behavior is erratic. Sometimes when I turn it on it starts keying right away. Or when I
touch the paddle. Same thing with a straight key in "hand" mode.
And when it gets in this state the menu button doesn't work, even if it is not
keying. All the other buttons seem fine.
I have a scope, so I looked at the /Bank1 and /Bank2 signals - all looks OK.
I checked the 82k resistor network for the /DOT-PTT and /DASH with an ohmmeter
- they look fine. 5 volts is there and good. ~80k to 5 volts on both signals.
But the dash is not pulling all the way up.
It is erratic - sometimes I can get it back to normal by pulling out the key
plug and so forth. But not often.
I removed the bottom panel with the heatsink screws (what a pain) and reheated
the key connector and looked at everything down there and traced the dot/dash
signals back - all looks fine.
So no obvious solution. I needed to upgrade the MCU firmware anyway, so I
ordered one.
It will be few days before I get that, but if you have another suggestion I
would appreciate it.
Thanks,
Sam N4MAP
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