[Elecraft] Help Please KIO2 L4 Burnt Out

[VK1OO]

Hi Guy,

Thought I would let you (and the reflector lurkers)  know the problem is 
solved, but I'm not sure how.
Not a connector issue - I did one of the mods a while back to prevent that.
I did check each of the power leads to the K2, KPA100 etc, but found no 
faults.  Subsequently measured the current through the L4 vias as as 
0.4mA. So perhaps checking each cable scared the fault away.  I inserted 
a new L4 and monitored the current for a few days with no observed 
issues.  Put the trusty K2 back together and no problems since. So, 
what's the best way to prevent a recurrence of this problem?

Mike
VK1OO


On 26-Apr-12 6:08 PM, Guy Olinger K2AV wrote:
> Yikes...   That certainly would do it.  Also if memory serves me 
> right, 260 ma is a typical K2 standing current in RX mode, almost as 
> if the negative power supply path to/in the K2 is just plain open 
> somewhere.  You will have to determine all the possible ground paths. 
>   Let all us curious folks know what you actually find.
>
> Then you will need to rearrange your station wiring so that simply is 
> not possible.  K2 should have its own dedicated power supply with 
> NOTHING else on it, the same as you hear preached around here for the K3.
>
> Good luck & 73,  Guy
>
> On Thu, Apr 26, 2012 at 2:45 AM, VK1OO <mike.walkington at gmail.com 
> <mailto:mike.walkington at gmail.com>> wrote:
>
>     Hi Guy,
>
>     Thanks
>
>     260mA!   Guess that would do it.
>     Exploring the power supply  etc now.
>
>     Mike
>
>
>     On 26-Apr-12 4:41 PM, Guy Olinger K2AV wrote:
>>     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
>>     <mailto: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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>