[Elecraft] KX-1 problem

[Don Wilhelm]

Neil,

I repaired a KX1 recently that had a shorted C44.  That was in addition 
to a relay that had apparently burned contacts, blown diodes in the 
wattmeter and a shorted 56 pf cap in the low pass filter.  That 
particular KX1 also had a bad DDS chip and one of the firmware chip 
outputs did not work.

The best guess I could give is that KX1 took a lightning surge.  The 
owner did let me know that he had inadvertently left it connected to his 
beam while he was away for the weekend.  The surge must have had enough 
voltage and current content to do the diode, capacitor, relay damage and 
just the residual floating around on the rest of the board damaged the 
DDS and firmware chip (those chips are at the far end away from the 
antenna and LPF) - of course, that is only a guess about the cause, but 
is the best I can offer.  Normally one finds only a single failed 
component - we do not expect multiple failures - when multiple failure 
do occur, it is usually the result of some external damaging force.  
Lightning induced damage can create some unpredictable problems.

C44 is pretty rugged, so it would take a good surge to cause it to 
short.  You may be fortunate and find that everything else is OK, but if 
you have other problems, suspect a lightning zap.

You dim LED is an indication that the KX1 is dragging down your battery 
supply voltage - there may be a capacitor on the +V voltage line that 
has developed a low series resistance.  You may want to arbitrarily 
replace C6 and C7 just in case, alternately hook it up to a good stiff 
power supply with adequate current capability and see what gets warm to 
the touch.

73,
Don W3FPR

Neil wrote:
> Hi all,
>
> I hooked up my KX-1 to a friend's dipole the other day and
> the sun stopped shining.
> Well, almost. My external 12V power supply shut itself off.
> Ouch. Why pulling
> so much current? 
>
> The dipole had a balun... I had not needed one for my
> previous antennas. There was
> 12V on the feedline and the balun was shorting it out. C44,
> in the final's collector
> circuit, was the culprit. Shorted. Of course, there could be
> other problems I haven't
> found yet.
>
> I've pulled the cap from the board, and need to purchase a
> replacement. That's next.
> Of course, I'll go through the voltage chart and verify
> everything is within spec.
> But there's another problem I think is probably related that
> I notice it when operating
> from a campsite recently. The LED work light is very very
> dim. Other than that,
> the KX-1 operated as usual into a 1/4 wave vertical I often
> use for portable operation.
> The shorted cap problem didn't show up with that antenna (no
> balun, no V+ short).
>
> Has anyone heard of this cap going south? Any suspicions
> about what might have
> caused it, and how to avoid it in the future? Thanks for any
> thoughts you KX-1ers, 
> or Elecraft folks, may have.
>
> BTW, I love this little rig. 
>
> Best, Neil  KH6EAM
>   
>