[Elecraft] K2 trouble on the tracks

Don Wilhelm w3fpr at embarqmail.com
Thu Nov 5 20:44:51 EST 2009


Dick,

That behavior is typical when the K2 is drawing too much current.  The 
resettable fuse (F1) on the RF board (right edge) trips.  Please confirm 
this by making the voltage measurement Ron suggested - if there is 
voltage on one leg of the fuse, but not the other, that is confirmation 
that the fuse is tripping.

IF the fuse is tripping, and IF you have a method of measuring the 
actual current draw externally, check to see if the current draw is 
coming close to 5 amps (the point where the resettable fuse trips).  If 
indeed the current is high, the fuse is OK and you need to look for the 
cause of the high current draw.

The normal cause of extremely high current draw is shorted PA transistors.
If you have good de-soldering equipment, you can remove those 
transistors to check the current with them not installed.
BUT if you think you will have trouble removing the transistors intact, 
then remove T3 (the bifilar wound toroid near the PA transistors).  
Removing that toroid will disconnect the 12 volts from the PA collectors 
and allow you to check the remainder of the K2.  If you remove the 
transistors or remove T3, you can safely operate the K2 without the heat 
sink (do not try that with 12 volts on the PA transistors or they will 
be damaged quickly).

73,
Don W3FPR

richard gilley wrote:
> My K2 was operating fine, has the SSB module the latest addition, and  
> The KTA100 addition.  Has been working fine for a week since the SSB  
> addition. Was on 80 meters tuning up on low power, 3 watts, and the  
> lights went out.
> Removed the KTA100 and SSB board on QRP with power to min, press  
> start: lights for 2 to 3 sec and quits.
>
> Where is the best place to start?
>
> Appreciate your help.
> Best regards
> Dick AD1G
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