[Elecraft] K2 PA runaway current

[Don Wilhelm]

Damon,

First, remove the KAT2 and operate the K2 into a good 50 ohm dummy load, 
and use some valid method of monitoring the actual power output.

If the same thing occurs, than look in the K2, but if it behaves 
properly, look at the KAT2.

If you have a K2 problem, How much is the power output?  You say the 
current builds up - over what time period?  What happens if you set the 
requested power to about 2 watts?  Do you still get the HI-Cur and how 
much power is actually being produced?

If it is a KAT2 problem, what happens if you operate at 2 watts with the 
ATU in CALP and a dummy load connected to the ANT1 output?  Have you 
nulled and calibrated the KAT2 wattmeter for correct power output 
indication?  If the K2 does not see the power output level being sent 
back from the KAT2, it will increase power to the maximum in an attempt 
to obtain the requested power output level so the KAT2 wattmeter must be 
calibrated for proper operation.

73,
Don W3FPR

Damon Wascom wrote:
> Hello elecraft list,
>
>      I need some help with troubleshooting my K2. I destroyed my finals (twice) due to a shorted cap (C4) in the KAT2. For troubleshooting purposes, the finals have been temporarily replaced with 2SC2078's ($0.68 vs. $6-11 for the 2SC1969's). My problem is when I TX at any band and any power setting the current starts to build until I get a Hi Cur warning. 
>
>      At this point i've: re-worked ALL solder joints on the RF board, performed signal tracing per the manual, inspected every component visually, checked the resistors and semiconductors in the TR switch and PA with my DMM (power off and voltages during TX) and pulled out my remaining hair. 
>
>      The same problem happens with the 2SC1969's in place so the substitution of the finals has been ruled out. I just don't want to fry any more (I can't tell my XYL oops, I did it again...)
> She is already upset with me about this. 
>
>      Here is my K2 configuration:
> K2 #: 06351 (15W), KNB2, KSB2, KAT2, KAF2, KIO2, K160RX, K60XV and KBT2.
> In other words, "Fully Loaded". 
>
>      I have been conducting tests with my MFJ-969's dummy load. My belief is that the problem is in the PA but that's just a guess. 
>
> Thanks, Damon KC5CQW
>
>