[Elecraft] Help Please KIO2 L4 Burnt Out

[Guy Olinger K2AV]

Do you have the DB9 plug that connects to the back of the KIO2 restricted
to pins 2,3, 5 ONLY?  See page 21 in the KIO2 manual. If you have hooked up
a full RS232 to the KIO2 DB9 there is no telling what has gone wrong, you
can cause all kinds of problems.

  http://www.elecraft.com/manual/KIO2_man_rev_B.pdf

Also L4 connects pin 5 of the common signal ground to the ground bus in the
KIO2.  If that goes through to a computer where a ground (black 12V lead)
has connected and your power supply to the K2 has a problem in the ground
(black) 12V supply wire to the K2 somewhere, and you have other devices
attached to the same power supply via common grounding, including what is
connected to the computer side of the USB cable, the ground current
attempting to flow via poor ground wire connection will attempt to find any
alternate route to the K2 any way it can.  That ground fault will blow L4
in the KIO2 board.

Take a DVM and see if you can draw current between pin 5 on the cable and
the ground of the K2.  If you can, you need to solve your power supply
problem.

73, Guy.

On Thu, Apr 26, 2012 at 1:47 AM, VK1OO <mike.walkington at gmail.com> wrote:

> Hi,
>
> My K2 rig control via a KIO2 stopped.  I discovered that RF sub
> miniature choke L4, 100 micro Henry,  on the main KIO2 board was open
> circuit - no evidence of excessive heat etc.  L4 is in the RS232 ground
> path.  Shorting out L4 restored rig control.  I replaced L4 with a
> larger version (all that I could find locally) but rig control didn't
> work.  I tested the new L4 and it was open circuit, again no evidence of
> excessive heat.  So the question is, what would cause excessive current
> through L4?
>
> I feed the KIO2 via a USB to RS232 converter which plugs into a four
> port USB hub which plugs into a lap top.  This combination has worked OK
> for several years.
>
> Mike VK1OO
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