Fw: Sudden erratic power/high current problems with K2

[NZ0T]

After some investigation I found that the braid of the coax for the Aux RF
had frayed at the KPA100 board to just a couple of strands.  Hoping this was
the problem I repaired it but no change.  This all seems to be caused by the
K2 power control being all or none with no intermediate settings.  In low
power as I turn the knob clockwise it goes from minimal power to full QRP of
about 12 watts suddenly and when the high power comes on it jumps to full
output.  How do I approach this problem?  Is it ALC related?
----- Original Message -----
From: "Bill Carpenter" <[hidden email]>
To: "elecraft list" <[hidden email]>
Sent: Saturday, December 22, 2007 12:38 PM
Subject: Sudden erratic power/high current problems with K2

> I'll try to keep this short.  I was operating with my K2/100 with KAT100
> today and everything was fine.  I changed bands and initiated tune on the
> KAT100 and it did not operate properly.  The SWR leds went a little
> bonkers and it did not want to settle on a low SWR.  I disabled it by
> going to CAL and then I noticed that even though the K2 power meter was
> showing about 2/3 scale I was getting full output on my outboard SWR
> meter.  I then took the KAT100 out of the loop by disconnecting it fully
> from the K2.  Now I am seeing very high power output of around 140 - 150
> watts on the lower bands such as 160, 80, 60, 30, 40 and 20 with more
> normal power output on the upper bands but I'm still seeing high current
> indication on all bands.  In addition the power control on the K2 is not
> working in a linear fashion. As I increase it from the lowest setting it
> is OK until the KPA100 kicks in when it suddenly goes to full output.  I
> have not ever seen this happen in the 15 months since I built the rig or
> in the 2 weeks since I built the KAT100 - everything has been fine.  Now
> all of a sudden I have all this erratic behavior.  As I said I added the
> KAT100 2 weeks ago but there have been no problems at all until now.
>
> Any and all help/suggestions are very welcome!!
>
> 73,
> Bill NZ0T

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[Don Wilhelm-4]

Bill,

That is classic behavior when the KPA100 wattmeter diodes are zapped.  
Since the most common failure cause is a static (lightning) surge from
the antenna, you may want to consider replacing the ones in the KAT100
at the same time.  The diodes are 1N5711s and in the KPA100 are D16 and
D17 (near the SO239 jack), and the diodes in the KAT100 are D1 and D2.

As explanation for the behavior, the K2 power control loop senses power
at the output with the wattmeters - if there is zero power out reported,
the controls drive harder - so you have a base K2 trying to drive as
hard as possible and the resulting output power is the maximum that can
be produced on any given band.  In other words, the wattmeter must be
working for the K2 to control the output power - that is the sensing
element.

73,
Don W3FPR


Bill Carpenter wrote:
> After some investigation I found that the braid of the coax for the
> Aux RF had frayed at the KPA100 board to just a couple of strands.  
> Hoping this was the problem I repaired it but no change.  This all
> seems to be caused by the K2 power control being all or none with no
> intermediate settings.  In low power as I turn the knob clockwise it
> goes from minimal power to full QRP of about 12 watts suddenly and
> when the high power comes on it jumps to full output.  How do I
> approach this problem?  Is it ALC related?
>
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[NZ0T]

I had some 1N4148 diodes in my junkbox so I installed them and all is good
again.  The diodes in the KAT100 are fine so I'll order a few 1N5711s and
replace the 1N4148s when they come in.

Thanks again!
----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Bill Carpenter" <[hidden email]>
Cc: "elecraft list" <[hidden email]>
Sent: Saturday, December 22, 2007 3:17 PM
Subject: Re: [Elecraft] Fw: Sudden erratic power/high current problems with
K2

> Bill,
>
> That is classic behavior when the KPA100 wattmeter diodes are zapped.
> Since the most common failure cause is a static (lightning) surge from the
> antenna, you may want to consider replacing the ones in the KAT100 at the
> same time.  The diodes are 1N5711s and in the KPA100 are D16 and D17 (near
> the SO239 jack), and the diodes in the KAT100 are D1 and D2.
>
> As explanation for the behavior, the K2 power control loop senses power at
> the output with the wattmeters - if there is zero power out reported, the
> controls drive harder - so you have a base K2 trying to drive as hard as
> possible and the resulting output power is the maximum that can be
> produced on any given band.  In other words, the wattmeter must be working
> for the K2 to control the output power - that is the sensing element.
>
> 73,
> Don W3FPR
>
>
> Bill Carpenter wrote:
>> After some investigation I found that the braid of the coax for the Aux
>> RF had frayed at the KPA100 board to just a couple of strands.  Hoping
>> this was the problem I repaired it but no change.  This all seems to be
>> caused by the K2 power control being all or none with no intermediate
>> settings.  In low power as I turn the knob clockwise it goes from minimal
>> power to full QRP of about 12 watts suddenly and when the high power
>> comes on it jumps to full output.  How do I approach this problem?  Is it
>> ALC related?
>>
>

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[Don Wilhelm-4]

Bill,

All will be well as long as you give some liberty to the requested vs.
actual power output while you have the 1N4148 diodes in there - the
1N5711s are pretty flat with respect to voltage vs. frequency.

Glad to hear you now have a handle on things again.

73,
Don W3FPR

Bill Carpenter wrote:

> I had some 1N4148 diodes in my junkbox so I installed them and all is
> good again.  The diodes in the KAT100 are fine so I'll order a few
> 1N5711s and replace the 1N4148s when they come in.
>
> Thanks again!
> ----- Original Message ----- From: "Don Wilhelm" <[hidden email]>
> To: "Bill Carpenter" <[hidden email]>
> Cc: "elecraft list" <[hidden email]>
> Sent: Saturday, December 22, 2007 3:17 PM
> Subject: Re: [Elecraft] Fw: Sudden erratic power/high current problems
> with K2
>
>
>> Bill,
>>
>> That is classic behavior when the KPA100 wattmeter diodes are zapped.
>> Since the most common failure cause is a static (lightning) surge
>> from the antenna, you may want to consider replacing the ones in the
>> KAT100 at the same time.  The diodes are 1N5711s and in the KPA100
>> are D16 and D17 (near the SO239 jack), and the diodes in the KAT100
>> are D1 and D2.
>>
>> As explanation for the behavior, the K2 power control loop senses
>> power at the output with the wattmeters - if there is zero power out
>> reported, the controls drive harder - so you have a base K2 trying to
>> drive as hard as possible and the resulting output power is the
>> maximum that can be produced on any given band.  In other words, the
>> wattmeter must be working for the K2 to control the output power -
>> that is the sensing element.
>>
>> 73,
>> Don W3FPR
>>
>>
>> Bill Carpenter wrote:
>>> After some investigation I found that the braid of the coax for the
>>> Aux RF had frayed at the KPA100 board to just a couple of strands.  
>>> Hoping this was the problem I repaired it but no change.  This all
>>> seems to be caused by the K2 power control being all or none with no
>>> intermediate settings.  In low power as I turn the knob clockwise it
>>> goes from minimal power to full QRP of about 12 watts suddenly and
>>> when the high power comes on it jumps to full output.  How do I
>>> approach this problem?  Is it ALC related?
>>>
>>
>
>
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>

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[Don Wilhelm-4]

Jeff,

I have never encountered an intermittent diode, but of course soldering
problems can create  an intermittent.  Also, you might have an
oscillation that is creating that behavior - it is difficult to say if
you are only looking at the output power - the actual frequency of the
output would reveal whether it is a parasitic oscillation or just a
power control intermittent.

One of the clues is that a parasitic oscillation will usually not show
up when working into a dummy load because the dummy load is not
frequency sensitive - when working into an antenna and/or an antenna
tuner, a parasitic will show up with a high SWR indication because the
load is frequency sensitive.

If your KPA100 was purchased before Nov 2006, it does not have the newer
T/R switch design, and you should upgrade it with KPA100UPKT.  If you
have already done that, be certain that C31 was changed to a 0.22 uF
capacitor with the upgrade.  The upgrade kit does not contain the new
capacitor for C31 - you must request one separately from
[hidden email].  There are steps in process to include the new C31
with the KPA100UPKT, but it is not yet complete.

73,
Don W3FPR

Jeff Kinzli N6GQ wrote:

> Don, would this behavior (of zapped wattmeter diodes) be intermittant,
> or constant? I have been chasing an intermittant high-output and
> erratic output problem for a while...just wondering if this might be
> my problem? Are these diodes particularly ESD-sensitive?
>
> Thanks,
>
> Jeff N6GQ
>  
>

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