[Elecraft] Fw: Sudden erratic power/high current problems with K2

[Bill Carpenter]

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" <w3fpr at embarqmail.com>
To: "Bill Carpenter" <nz0t at cox.net>
Cc: "elecraft list" <elecraft at mailman.qth.net>
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?
>>
>