K2 - Fuses ...A Cautionary Tale

[k6dgw]

With a feeling of great stupidity coupled with a desire to prevent this
for others:

Yesterday, I reassembled my K2 [#4398, Sep 2004] with the QRP top and
KAT2, having just sold my KPA100.  I was interrupted by a phone call
after plugging the edge connector and speaker in.  When I returned, I
plugged the KAT2 coax into ... AUX 12V, grounding the 12V. :-((
Finishing the assembly, I decided to quickly power it up just to make sure.

Now, the cables I normally use with the K2 and KX1 have in-line fuses,
and I have just converted all the DC in the shack to APP.  The power
supply was at the other end of the desk, so I grabbed the LiFePO4 15C
battery, plugged in one of my little adapter jumpers [APP to coaxial
power] ... no fuse ... and plugged it into the K2.  I heard a distinct
click, I wondered if the on/off switch was on, it wasn't, I turned it
on, and radio was dead.  At this point, I noticed the distinct odor of
misrouted electrons, an odor we all recognize, and removed the battery.

With no fuse, the heavy trace between the power connector and hot end of
C196, way above and beyond its call of duty, sacrificed itself.
Fortunately, the trace is now replaced by a short jumper wire and the
radio works.  D10 seems to have survived, probably because, when used as
a fuse, a PCB trace is ultra-fast.

A colleague of mine once said, "The problem with 'Lessons Learned' is
that they rarely are."  Thus encouraged, my lessons from this are:

1.  Never connect any power to any radio without an in-line fuse.

2.  Tape or otherwise cover AUX 12V unless you're actually using it [KPA100]

3.  Just because you've done something many times does not mean you'll
get it right on the many+1'th time.  Many years ago in military uniform,
I knew this.  I guess I just forgot.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org
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[k6dgw]

On 12/22/2011 12:57 PM, Ron D'Eau Claire wrote:
> Ouch! You might consider adding a .01 or .1uFd cap in series with the RF
> input to the KAT2 so it would show an open circuit to dc.
>
> IIRC, that was done to the RF input to the KPA100 for just that reason.

Well ... the two AUX males on the RF board are the same and oriented
identically, so to do what I did automatically put the +12V on the
shield.    Were my K2 an airplane, it probably would have been
impossible to cross-connect them, but even that isn't always true.  I
saw a fly-by-wire fighter aircraft which will remain nameless get a
goodly way down the runway, start to lift off, do an immediate snap roll
and "land" inverted.  Someone had managed to get the connectors to the
pitch and roll gyros crossed.

Yet again I find out there is no substitute for attention to details.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org
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[Don Wilhelm-4]

OK -- There are *dumb* things, and there are *stupid* things - and
sometimes it is difficult to separate the two.  So go write yourself a
"dear dummy" letter and let it go at that.

Yes, the two connectors for AUX RF and AUX 12V are the same, and if
exchanged, you will have a DC short to ground - better to sacrifice a
bit of PC trace than to encounter significant component damage.  I don't
see that exchanging the two connectors is a major hazard - the KPA100
(or KBT2) connector if built to the specified length is not long enough
to interchange the connectors easily - yes, it is possible, but not easy.

Check that the length of your AUX 12V leads are the correct length (4.5
inches) and that the input coax to the KPA100 is the correct length
(also 4.5 inches) and it should be difficult to connect both cables to
the K2 RF board with the cables reversed - while it is possible, it is
not as easy as connecting them correctly.

So, the bottom line is (IMHO) - fuse all DC sources at the rating for
the load, and follow instructions.  For those times when you do not do
things correctly and S**T happens, just say "AH S**T" and go on with
life as it may be.

I used to work for IBM, and there was a desk plaque that had the word
"THINK" on it.  Well, that is what I am asking you to do - "THINK" - it
will make a lot of difference.  BTW, the publication "Think" is now the
property of Case Institute of Technology (My Alma-mater), and is the
official alumni magazine.

73,
Don W3FPR

On 12/22/2011 6:05 PM, Fred Jensen wrote:

> On 12/22/2011 12:57 PM, Ron D'Eau Claire wrote:
>> Ouch! You might consider adding a .01 or .1uFd cap in series with the RF
>> input to the KAT2 so it would show an open circuit to dc.
>>
>> IIRC, that was done to the RF input to the KPA100 for just that reason.
> Well ... the two AUX males on the RF board are the same and oriented
> identically, so to do what I did automatically put the +12V on the
> shield.    Were my K2 an airplane, it probably would have been
> impossible to cross-connect them, but even that isn't always true.  I
> saw a fly-by-wire fighter aircraft which will remain nameless get a
> goodly way down the runway, start to lift off, do an immediate snap roll
> and "land" inverted.  Someone had managed to get the connectors to the
> pitch and roll gyros crossed.
>
> Yet again I find out there is no substitute for attention to details.
>
> 73,
>
> Fred K6DGW
>

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[Rick WA6NHC]

And don't do this again because now that the melted trace has been replaced
with a wire, which can likely handle more current, you'll break something
else farther down the chain.  :-\

Glad it was easily fixed,

Rick WA6NHC

-----Original Message-----
From: Don Wilhelm

OK -- There are *dumb* things, and there are *stupid* things -

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[Don Wilhelm-4]

Rick,

It is not likely to "break something further down the chain" --
The K2 has a resettable fuse that will limit the fault current to 5
amperes or less.  The PC trace that was fried was before the resettable
fuse.

73,
Don W3FPR

On 12/22/2011 7:55 PM, Rick Bates wrote:
> And don't do this again because now that the melted trace has been replaced
> with a wire, which can likely handle more current, you'll break something
> else farther down the chain.  :-\
>
> Glad it was easily fixed,
>
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[k6dgw]

In my case, Don is entirely correct, the ground occurred prior to the
resettable fuse, and the only thing in the path was the trace from the
power connector through D10 to the AUX 12V pin.  And, believe me, I will
never "just check to see if it's all OK" again without a fused power
lead.  It was a stupid mistake on my part, driven by haste ... and I'm
not sure why, I know better.

Rick has a good point however:  Someone mentioned The Ampere Theorem,
"Any short circuit will eventually find a fuse."  A corollary is, "Make
that bigger, it will find something else."  I escaped that this time,
won't every time unless I pay attention.

I think the bigger lesson for me is, "Pay attention to the details.
This wouldn't have happened had I not plugged into the wrong connector,
I *know* the right connector and have done it right many times, I just
wasn't paying attention.  I still put one hand in my pocket, or sit on
it, when poking in live gear even though 12V won't electrocute me.  Some
old habits won't die.  Paying attention seems to have stuttered a bit on
this one.

Shorts on power leads, inside and outside the radio, can happen.
Today's batteries have some incredible energy densities and can deliver
huge currents.  They may not electrocute you but they can sure burn you
and fry your radio.  Fuse every power lead.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2012 Cal QSO Party 6-7 Oct 2012
- www.cqp.org

On 12/22/2011 5:09 PM, Don Wilhelm wrote:
> Rick,
>
> It is not likely to "break something further down the chain" --
> The K2 has a resettable fuse that will limit the fault current to 5
> amperes or less.  The PC trace that was fried was before the resettable
> fuse.
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[Don Wilhelm-4]

Fred,

That is great advice - "Fuse every lead".   "Whatever happens" is still
good advice.
If there is any question about the power supply, I will first ask about
it, then about the current being drawn.  So if you have something
marginal, that will be revealed at the outset - proper connectors not
withstanding.

"Pay attention" is by far and large the best advice.  It is the
cautionary tale of old which advised us to keep the left hand in the
pocket so high voltage paths would not have a direct path through the
heart area of the body

So to me, "PayAttention" is more than an attention getter, it is a way
of life that allows one to pay attention to all aspects of the
situation.  In other words PAY ATTENTION - your life may depend on it.
Voltage may kill. but current can maim - so consider both low voltage,
high current sources as well as high voltage sources with equal respect
- they are both are a source of power which deserves respect for safety..

73,
Don W3FPR

12/22/2011 10:48 PM, Fred Jensen wrote:

> In my case, Don is entirely correct, the ground occurred prior to the
> resettable fuse, and the only thing in the path was the trace from the
> power connector through D10 to the AUX 12V pin.  And, believe me, I will
> never "just check to see if it's all OK" again without a fused power
> lead.  It was a stupid mistake on my part, driven by haste ... and I'm
> not sure why, I know better.
>
> Rick has a good point however:  Someone mentioned The Ampere Theorem,
> "Any short circuit will eventually find a fuse."  A corollary is, "Make
> that bigger, it will find something else."  I escaped that this time,
> won't every time unless I pay attention.
>
> I think the bigger lesson for me is, "Pay attention to the details.
> This wouldn't have happened had I not plugged into the wrong connector,
> I *know* the right connector and have done it right many times, I just
> wasn't paying attention.  I still put one hand in my pocket, or sit on
> it, when poking in live gear even though 12V won't electrocute me.  Some
> old habits won't die.  Paying attention seems to have stuttered a bit on
> this one.
>
> Shorts on power leads, inside and outside the radio, can happen.
> Today's batteries have some incredible energy densities and can deliver
> huge currents.  They may not electrocute you but they can sure burn you
> and fry your radio.  Fuse every power lead.red K6DGW
> - Northern California Contest Club
> - CU in the 2012 Cal QSO Party 6-7 Oct 2012
> - www.cqp.org
>
> On 12/22/2011 5:09 PM, Don Wilhelm wrote:
>> Rick,
>>
>> It is not likely to "break something further down the chain" --
>> The K2 has a resettable fuse that will limit the fault current to 5
>> amperes or less.  The PC trace that was fried was before the resettable
>> fuse.
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[DaveL G3TJP]

Just one other caution, if I may.

Before dabbling inside any piece of equipment where a current can possibly
flow, remove any rings from your fingers and remove your wristwatch and any
other conductive material.  If they happen to be on the hand in your pocket,
so be it, but don't forget that if something happens, you may react without
thinking and put that left hand into service.

Season's Greetings, everyone.

 

73  Dave  G3TJP

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[Alan Davenport]

What I do if I let the smoke out of a trace is to replace the burned portion of the trace with a SINGLE strand from some braided wire. In effect, reapiring the burned trace with a fuse.
 
   73 de Al, W2GZN
 

________________________________
 From: Rick Bates <[hidden email]>
To: [hidden email]
Sent: Thursday, December 22, 2011 7:55 PM
Subject: Re: [Elecraft] K2 - Fuses ...A Cautionary Tale
 
And don't do this again because now that the melted trace has been replaced
with a wire, which can likely handle more current, you'll break something
else farther down the chain.  :-\

Glad it was easily fixed,

Rick WA6NHC

-----Original Message-----
From: Don Wilhelm

OK -- There are *dumb* things, and there are *stupid* things -

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[aj4tf]

I took a Sharpie that had laying on my workbench, and "changed the
color" of the aux power connector both on the board and the wiring
harness, which is what the manual suggests, IIRC.  No, it doesn't
prevent one from swapping them, but is a visual indication which one
goes where.   One still has to take their time when working on a $1000
piece of equipment.  Glad you got it fixed and nothing else was smoked
besides the PC board trace.

73, David  
AJ4TF

>
> Message: 7
> Date: Thu, 22 Dec 2011 12:08:43 -0800
> From: Fred Jensen <[hidden email]>
> Subject: [Elecraft] K2 - Fuses ...A Cautionary Tale
> To: Elecraft Reflector <[hidden email]>
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>
> With a feeling of great stupidity coupled with a desire to prevent this
> for others:
>
> Yesterday, I reassembled my K2 [#4398, Sep 2004] with the QRP top and
> KAT2, having just sold my KPA100.  I was interrupted by a phone call
> after plugging the edge connector and speaker in.  When I returned, I
> plugged the KAT2 coax into ... AUX 12V, grounding the 12V. :-((
> Finishing the assembly, I decided to quickly power it up just to make sure.
>
> Now, the cables I normally use with the K2 and KX1 have in-line fuses,
> and I have just converted all the DC in the shack to APP.  The power
> supply was at the other end of the desk, so I grabbed the LiFePO4 15C
> battery, plugged in one of my little adapter jumpers [APP to coaxial
> power] ... no fuse ... and plugged it into the K2.  I heard a distinct
> click, I wondered if the on/off switch was on, it wasn't, I turned it
> on, and radio was dead.  At this point, I noticed the distinct odor of
> misrouted electrons, an odor we all recognize, and removed the battery.
>
> With no fuse, the heavy trace between the power connector and hot end of
> C196, way above and beyond its call of duty, sacrificed itself.
> Fortunately, the trace is now replaced by a short jumper wire and the
> radio works.  D10 seems to have survived, probably because, when used as
> a fuse, a PCB trace is ultra-fast.
>
> A colleague of mine once said, "The problem with 'Lessons Learned' is
> that they rarely are."  Thus encouraged, my lessons from this are:
>
> 1.  Never connect any power to any radio without an in-line fuse.
>
> 2.  Tape or otherwise cover AUX 12V unless you're actually using it [KPA100]
>
> 3.  Just because you've done something many times does not mean you'll
> get it right on the many+1'th time.  Many years ago in military uniform,
> I knew this.  I guess I just forgot.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the 2012 Cal QSO Party 6-7 Oct 2012
> - www.cqp.org
>
>

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[Phil Kane-2]

On 12/23/2011 5:35 AM, Alan Davenport wrote:

> What I do if I let the smoke out of a trace is to replace the
> burned portion of the trace with a SINGLE strand from some
> braided wire. In effect, reapiring the burned trace with a fuse.

  When I lived in the Middle East in the mid-1960s that's how
  they actually made fuses in residential power boards - each
  strand was rated for 10 A.  !

  On Topic - has any determination ever been made on the use of a
  12-V marine-rated circuit breaker versus a 3AG/ATC cartridge fuse
  in a distribution panel for Elecraft equipment installations?

--  73 de K2ASP - Phil Kane
    Elecraft K2/100   s/n 5402

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