KAT100: No SWR Indication

[Jonathan Taylor, K1RFD]

After working OK for several years, my KAT100 no longer indicates SWR, nor
does it tune properly.

When used with my K2/100, in ATU Auto mode, with the TUNE button, the
KAT100 starts finding a match as expected.  However, none of the SWR LEDs
illuminate, and the K2 display indicates 1.0-1 SWR during the entire
search.  I am not at all convinced that it has found a good match once the
tuning sequence completes.  An SWR bridge placed between the K2 and the
KAT often shows a poor match after tuning.

I suspect a problem in the KAT's SWR bridge, but does anyone have specific
troubleshooting advice?

Thanks!


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[Don Wilhelm-3]

Jonathan,

If it was working before, it may be that the wattmeter bridge diodes in
the KAT100 were zapped with a lightning surge.

I suggest the first step is to obtain 2 1N5711 diodes and replace D1 and
D2.  While you are doing that, check the soldering/tinning on the leads
of T1.  If that does not restore normal operation, other tests may be done.

BUT - if it has NOT worked properly before, you may have other problems.
  In that case, check T1 very carefully to be certain the correct leads
are in the proper holes and the leads are well tinned and soldered.

In the future, for your personal safety and the health of your
equipment, disconnect antennas when not in use.

73,
Don W3FPR

Jonathan Taylor, K1RFD wrote:
> After working OK for several years, my KAT100 no longer indicates SWR, nor
> does it tune properly.
>
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[Jonathan Taylor, K1RFD]

Don,

Thanks for the advice.  That's a strong possibility, since I just
performed the same successful repair on my KPA100, which may have been
inline at the same time.

On this topic: A friend suggested putting a 1 megohm resistor across the
antenna terminals to help dissipate static charges when used with an
antenna that is "open" from a DC perspective, such as a dipole.  Is this
good advice?

> Jonathan,
>
> If it was working before, it may be that the wattmeter bridge diodes in
> the KAT100 were zapped with a lightning surge.
>
> I suggest the first step is to obtain 2 1N5711 diodes and replace D1 and
> D2.  While you are doing that, check the soldering/tinning on the leads
> of T1.  If that does not restore normal operation, other tests may be
> done.
>
> BUT - if it has NOT worked properly before, you may have other problems.
>   In that case, check T1 very carefully to be certain the correct leads
> are in the proper holes and the leads are well tinned and soldered.
>
> In the future, for your personal safety and the health of your
> equipment, disconnect antennas when not in use.
>
> 73,
> Don W3FPR
>
> Jonathan Taylor, K1RFD wrote:
>> After working OK for several years, my KAT100 no longer indicates SWR,
>> nor
>> does it tune properly.
>>
>
>
>

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[Jonathan Taylor, K1RFD]

For the sake of the Archives, here's the epilogue.

I replaced D1 and D2, with no change in behavior.  Tracing showed that
there was close to 0V at the outputs of U5 during transmit.  With power
off, the resistances at the inputs of U5 were about 10 ohms!  The op amps
must have been zapped as well.  I replaced U5 and now all is well.  (I
also repeated the Power Calibration alignment step).

Thanks for the help.

73
Jonathan

> Jonathan,
>
> If it was working before, it may be that the wattmeter bridge diodes in
> the KAT100 were zapped with a lightning surge.
>
> I suggest the first step is to obtain 2 1N5711 diodes and replace D1 and
> D2.  While you are doing that, check the soldering/tinning on the leads
> of T1.  If that does not restore normal operation, other tests may be
> done.
>
> BUT - if it has NOT worked properly before, you may have other problems.
>   In that case, check T1 very carefully to be certain the correct leads
> are in the proper holes and the leads are well tinned and soldered.
>
> In the future, for your personal safety and the health of your
> equipment, disconnect antennas when not in use.
>
> 73,
> Don W3FPR
>
> Jonathan Taylor, K1RFD wrote:
>> After working OK for several years, my KAT100 no longer indicates SWR,
>> nor
>> does it tune properly.
>>
>
>
>

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