[Elecraft] K2 Problems

[Don Wilhelm]

Brent,

If I were you, I would order 2 1N5711 diodes (PN E560004).

I suspect that your original problem is that KPA100 diodes D16 and D17 
were damaged by static, with the result that the KPA100 output was at 
maximum (150 t0 180 watts) no matter what the power setting. That 
condition continued for long enough will place stress on the base K2 PA 
transistors and they will die of overload.

I just  recently responded to a similar private enquiry, I copy my 
response below..

Replace Q11 and Q13 since they also can be damaged as a secondary effect.
---------------------------------------------------------------------------------
If you did not try to transmit for long after you saw the HiCur display, 
the base K2 PA transistors may still be OK.

Your main problem is that the KPA100 wattmeter diodes have either 
shorted or opened, so the K2 can no longer determine power output. Since 
the K2 MCU thinks there is zero power output, it increases drive to the 
maximum - an external wattmeter will normally show 150 to 180 watts.  
That does place stress on the base K2 PA transistors which may fail as a 
secondary effect.

If that describes your situation, replacement of KPA100 D16 and D17 may 
normally set things in order again.

To prevent similar further incidents  make certain there is a good DC 
path across the feedline of all your antennas.

"Other transceivers do not have this problem" will fall on deaf ears 
here.  The "other transceivers" control power output only by changing 
the drive to the final stages.  Elecraft products actually measure the 
power at the output stage and control the power output by a closed 
control loop.  That does require sensitive diodes at the output of the 
PA, but it also means that those diodes are susceptible to static 
charges on the antenna.

Static on the antenna can be caused by wind, rain, sleet, snow or nearby 
lightning charges.
A 2 or 3 watt resistor with a value between 5000 ohms and 100k ohms 
across each feedline will be a great help in reducing the number of 
failures of KPA100 wattmeter diodes.
--------------------------------------------------------------------------------------------------

73,
Don W3FPR

On 8/23/2012 7:47 PM, Brent Sutphin wrote:
> We had a storms in the area here yesterday. Afterwards my K2-100 would not
> stay on.  When I turned it on, it came on for a few seconds then a high
> current warning and then off.  Long story short I determined that the K2 rf
> power transistors are bad.  I plan to order new ones tomorrow.  Question is,
> do I need to look further?
>
> Brent  WB4X
>
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