KX-1 problem

[Neil -2]

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

Neil Murphy
www.ghostdog.com
650.375.0886 wrk
650.533.2015 mobile

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[Don Wilhelm-4]

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
>  
>

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