Re: K2/100 Has No Output on 80 or 40 When Hot

Posted by Don Wilhelm-4 on Jun 01, 2010; 1:07pm
URL: http://elecraft.85.s1.nabble.com/K2-100-Has-No-Output-on-80-or-40-When-Hot-tp5124474p5125883.html

Phil,

To use the base K2 BNC antenna jack, you must remove the KPA100 - if you
attempt to use that jack, the load impedance between the base K2 and the
KPA100 will not be correct, and "strange happenings" will be present.

A total lack of power (yes, a display of 0.1 or 0.2 watts is actually no
power out) is most likely a problem either in the bandpass filter or a
problem with the VFO.  Try the VFO first - set the frequency to the low
end of the band and check the frequency with the counter probe in TP1
using CAL FCTR - compare your frequency reading with the chart on the
Schematic Key page.  If you want to calculate the proper VFO frequency
it should be within a few kHz of the frequency on the dial plus 4915 for
bands below 15 meters.

Check all the components in the bandpass filter area for 40m and for 80
meters.  On 40 meters, be certain C6 is properly installed between the
two outer holes of the J15 position (the center hole should be empty).

73,
Don W3FPR

Phil-W6TQG wrote:

> Every since the last Field Day, my K2/100 (#3713) loses output, and the
> receiver goes dead, on 40m and 80m when it gets hot. This occurs for
> power levels of 9 watts and 100 watts. The 30m through 10m bands are OK.
> I can easily replicate the problem when the power amp is connected, but
> so far it seems to be OK when it is completely unplugged from the K2.
>
> Turning off the power amplifier through the Secondary Menu does not make
> a difference. While transmitting at 9W, the readings on the display for
> 40 and 80 are "0.1 1.01 - 1". With the power amplifier connected to the
> K2, I temporarily connected the antenna to J4 on the K2, so that I could
> bypass the power amplifier path. This did not help the dead reception on
> 40 or 80. I also tried connecting a dummy load through a power meter to
> J4 and transmitting at 9W. Again 40 and 80 didn't work but the higher
> bands were OK.
>
> I am assuming that the problem is in the LPF of the power amplifier, but
> am not sure 30m is OK, while 40 and 80 are not. Any hints would be
> appreciated.
>
> 73,
> Phil W6TQG
>
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