[Elecraft] K2 - Fuses ...A Cautionary Tale

[Fred Jensen]

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