K2/100 - Can not control output power levels

[VK2IA]

Hi,

I'm new to this email list.

Never had a problem with my K2 until recently when I noticed that it only transmits at 2 fixed power levels (measured at 7w and 70w approx) despite display showing continuous power levels when changing power settings with potentiometer.

Suspect a broken pot (I think it's a linear 5K pot) but could be more complex than that.  

Any comments would be very much appreciated.

[Don Wilhelm-4]

If you only have 2 power output levels, I do believe your problem is
much different than a broken pot.
The K2 does not use the knob setting directly to adjust the power.  It
measures the actual output power and compares it to the power you set
with the power pot.  If the measured power is not up to the level
expected, then the MCU adjusts the drive to produce an output that the
K2 "thinks" is correct.

The fact is that your most likely problem is a fault in the wattmeter in
your KPA100.  The most common cause of that failure is damaged diodes
D16 and D17.  The wattmeter sits right at the antenna connection to the
KPA100 and if there is any static charge (from lightning, wind static,
rain static, snow static) those diodes can easily be damaged.

A DC path across your antenna feedline will go a long way toward
assuring continued health for those diodes.  A 100 uHy choke with
adequate current rating for your maximum power will work, but a resistor
in the range of 5k to 20k - I would suggest 1 to 3 watt rating for the
resistor.

For now, check those diodes in your KPA100 to see if that is your
problem (I think it is).  Why it is limited to 7 watts and 70 watts, I
have no idea - when the diodes go out, the power goes to its maximum
capable power (which might cause other damage).  I can either conclude
that you do not have an accurate power measuring capability or that
something further has been damaged in the K2 or KPA100.

73,
Don W3FPR

On 1/15/2012 7:06 PM, VK2IA wrote:

> Hi,
>
> I'm new to this email list.
>
> Never had a problem with my K2 until recently when I noticed that it only
> transmits at 2 fixed power levels (measured at 7w and 70w approx) despite
> display showing continuous power levels when changing power settings with
> potentiometer.
>
> Suspect a broken pot (I think it's a linear 5K pot) but could be more
> complex than that.
>
> Any comments would be very much appreciated.
>
>
> -----
> 73
> Bernd VK2IA-VK6AA
> K2 #5513
> K3 #0133
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-100-Can-not-control-output-power-levels-tp7191013p7191013.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html