[Elecraft] [K3] short circuit at power terminals

[Dale Boresz]

Hello Lewis,

I experienced this same issue once, and the problem ended up being the 
Transil diode D28 on the main pc board, near the 12 vdc power input 
connection. It is a large diode, and I believe it's purpose in life is 
to protect against excessive input voltage. It should begin to draw 
current when the voltage goes too high, and that should blow the 
resettable fuse F1. In my case, I was running the power supply voltage 
at about 15.0 vdc, and I suspect that my particular diode may have had a 
slightly lower threshold than normal, and was probably drawing current 
and dissipating power, though not enough to blow the F1 fuse -- until it 
failed completely by short circuiting. (This is just a guess; The 
replacement that I received from Elecraft has been working fine though.)

If you can, try measuring the resistance in both directions across diode 
D28. To really prove it though, you'd need to lift at least one end of 
that diode and then measure it.

Spec sheet on the diode:

< 
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000695.pdf 
 >

Best of luck with your troubleshooting.

73, Dale
WA8SRA

On 10/19/2012 2:50 AM, Lewis Phelps wrote:
> Yikes!  My reliable K3-10 has developed a short circuit across the power input terminals.  Well, to be exact, not quite a dead short. It measures 0.6 ohms across the PowerPole connectors. It most certainly does blow fuses on the input line.
>
> Any suggestions for trouble shooting?  And also for a possible cause of the problem?
>
> Lew N6LEW
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