[Elecraft] K2 s/n 4276 Output Power Instability

[Don Wilhelm]

William,

You said 40, 30 and 20 worked once, but not now - that says any problem 
is in an area shared by all bands.
The first thing to do would be to check the coax cables, any adapters 
and the dummy load for a bad connection.  I prefer to reduce any extra 
things in the setup because they too can be a source of trouble (and 
they are often overlooked).  Connect the K2 using a short piece of known 
good coax to a known good dummy load and try again.

If you continue to have problems, go back to 40 meters (which once 
worked) and use the Transmit Signal Tracing steps in the back of the 
manual to determine the failing stage.  If you have not already 
constructed the RF Probe from the supplied parts, now is a good time to 
do that.

We can help further if we know more about the failing stage or stages - 
right now, all we can say is that something is wrong somewhere - either 
inside or outside the K2.

I would not suspect U6 at this point - if you have a problem with the 
power control only, take a critical look at the Keying waveshape 
components mounted on the back of the Control Board (yes, they are part 
of the power control loop).

73,
Don W3FPR

kc4wvl wrote:
> K2 s/n 4276
> Firmware Revision(s):  2.04P  1.09
>
> After having a previous issue with the VCO alignment (p. 61), construction went forward without a hitch. At this point, I figured that any gremlins had been banished. Not so.
>
> Another pesky gremlin has reared it's ugly head.  During transmitter alignment, the initial 40 meter alignment went down in accordance with the manual's expectations.  Receiver pre-alignment was straight forward.  Alignment of 20 and 30 meter transmit went fine, then from that point on,  it all went downhill and the current issue began.  Regardless of which band or power setting, on entering TUNE, the power out readings rapidly vary across the entire scale. These rapidly changing readings are also reflected on my Diamond SK-600 power/SWR meter as well as the readigs on the current meter of the power supply.  After a brief bit of time, the power out will sometimes stop fluctuating and settle down to the requested power setting. 
>
> Might this be a problem with U-6, on the control board?
>
>