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[K3] short circuit at power terminals

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Lewis Phelps

[K3] short circuit at power terminals

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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dmb@lightstream.net

Re: [K3] short circuit at power terminals

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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

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Lewis Phelps

Re: [K3] short circuit at power terminals

In reply to this post by Lewis Phelps

Thanks for the input. No, I haven't had the rig open in more than a year. It hasn't moved from its current operating position in weeks.
No rattling loose screws.

There is a strong possibility that the input was over-voltaged due to a short in a separate piece of equipment that was powered from the same 12VDC buss. The other item has both 12VDC and 24 VDC inputs, and it's possible that the 12V line got "bumped up" to 24V. That would be consistent with Dale's description of the issue. I will pull the cover off later this afternoon or tomorrow morning and check the diode, and look for any obvious places where the smoke has been let out of a component.

Thanks for the good feedback, guys.

Lew N6LEW

On Oct 19, 2012, at 7:11 AM, "Jim Miller" <[hidden email]> wrote:

> First thought: Is there any chance you may have dropped something (screw,
> etc.) into it at any time and now it has moved to create the short? Remove
> covers and turn it every which way and shake it and even bump it firmly with
> you palm over a table or non-carpeted floor and listen carefully.
>
> Now the questions: Have you had the covers off and now it doesn't work?
> Were you installing or removing options? Disconnect or remove them to
> isolate.
> What have you done "recently" other than operate it?
> Have you moved it?
> Were you poking around inside so a connector came loose and is now touching
> ground?
>
> Isolation of the problem: I had a phono jack on the back that lost
> conductivity with ground and blew up my amp by allowing power into the amp
> without pulling the transmit line active. I chased the problem by using the
> minor resistance differences to get close to the problem area and then found
> 2 of the phono jacks were soldered but no connection to ground. Wire bridge
> to another ground point solved my problem. Try to remove/unplug/otherwise
> disconnect components to remove the short. You may even find that screw you
> lost during construction. Hi hi
>
> Good luck, Having a K3 not working really SUCKS.
>
> 73, de Jim KG0KP
>
> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Lewis Phelps
> Sent: Friday, October 19, 2012 1:50 AM
> To: [hidden email] List
> Subject: [Elecraft] [K3] short circuit at power terminals
>
> 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
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
>

Fred Townsend

Re: [K3] short circuit at power terminals

In reply to this post by Lewis Phelps

Lew, with a good digital ohm meter and 0.6 ohms of resistance you can
sometimes walk down the traces looking for a 0.0 (or as low as your test
leads measure) short. This doesn't always work since your problem may not be
a dead short but it is a simple starting point before going into more
advanced trouble shooting.
73
Fred, AE6QL

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Lewis Phelps
Sent: Thursday, October 18, 2012 11:50 PM
To: [hidden email] List
Subject: [Elecraft] [K3] short circuit at power terminals

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
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
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