[Elecraft] K2/100 power maxes out

[W3FPR - Don Wilhelm]

Brian,

If I understand your wording correctly, no matter whhere you set the power
level <10 watts, the K2 output is 14 to 15 watts, and if the power level is
set for >10 watts the output is 100 watts (or more).  (Should I have
misunderstood, ignore the rest.)

The normal cause of that behavior is some failure in the wattmeter circuit -
and the net result is that the VRFDET signal to the microprocessor indicates
no power is being transmitted, so the K2 firmware responds by increasing
power in an attempt to obtain 'sufficient' output - yes, it really is
sufficient, but the microprocessor is not getting the signal to tell it so.

To find out where the failed component is, turn the power to less than 10
watts, connect a dummy load.  Then transmit for brief periods while
monitoring voltage at the following points (you are looking for the presence
of a 'healthy' voltage, and not a specific voltage - you only need to find
where the path is broken).
U5 pin 5   -- voltage direct from the wattmeter calibration pot
U5 pin 7  -- buffer output
U6 pin 3  -- VRFDET driver input
U6 pin 6  -- VRFDET driver output

If you have a voltage at U6 pin 3, but not at pin 6, then check the voltage
at U6 pin 8 - it should be about 5 volts during transmit.

If all is well at the points above, the problem is with the VRFDET signal on
the K2 control board, or possibly a break in the 10 conductor ribbon cable
(pin 10)

BTW, if you have the KPA100 in a separate enclosure, you may want to check
the cable that goes from the KIO2 to the KPA100 for continuity on pin 7.

73,
Don W3FPR

> -----Original Message-----

>
> Hi all:  I got no response, so I thought I'd try to be a little
> clearer.  My
> K2 was working fb, in all regards.  Suddenly, it maxes out at about 14-15
> watts, regardless of the power setting.  With power set >10 watts, kicking
> in the amp, this naturally leads to output of 100 watts, regardless.
>
> I did a complete reset, but the symptoms remain the same.  Can anyone
> suggest a starting point to trouble shoot?  Tnx de Brian W3BW
>
>
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