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

[Don Wilhelm]

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
>