K2 Intermitt

[TR K2 #838]

Dear Elecrafters,

For some years now my K2/100 S/N 838 has had an intermitt.

When I take it to a new location, it is generally jostled somewhat in
moving it and hooking it up.

When all installed, everything works perfectly,... then...

Without warning, the received tone on the other guy gets "holes" in
it.  Like a noise blanker is cutting out the audio on noise bursts,
only the noise blanker is off and these holes are much bigger than
noise blanker holes.  The holes get bigger and bigger until you can't
read the other station, then, mysteriously, they go away and all is
normal.  If you are transmitting during one of these episodes, the
other station will report that you are breaking up.

Whatever it is, affects both transmitt and receive the same.

Some years ago I discovered that unplugging the anderson power
connector on the rear and plugging it back in cleared the problem,
but it troubled me that this is not a very good way to turn
transistors on and off and it could result in transients.  It
certainly made a loud "pop" in the loudspeaker.  Obviously, there was
a problem in the power cord !  So the cord was replaced and the VCC
was measured during a breaking up episode and found to be stable
inside the K2/100.  So it was not the power cord.

The next solution was to turn K2 on it's left side and hit it with a
good smart "whack" with my fist.  After one or two of these, the
problem clears and does not come back until K2 is taken on a trip,
and then it starts up again.

An "easy fix" and much less potentially destructive than jerking the
power cord in and out.  Never the less, still embarrassing on field
day when I'm out with the "boys."

Does anyone have an idea what might be causing this ?

Thanks,

TR, WB6TMY
K2/100 S/N 838



Tel: . . . [phone]

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[Don Wilhelm-4]

TR,

Those conditions sound like you have an intermittent connection inside
that K2 somewhere.  Since it is a problem for both transmit and receive,
it could be in the BFO or the PLL/VCO circuits.
If it only occurs on one or two bands, then the problem spot could be
either the bandpass filter or the low pass filter, but if it occurs on
all bands, it must be in either the BFO or VCO.

If I had to take bets, I would say the BFO is the more likely.  I would
replace the BFO crystals (which means a new filter alignment), the 2
Varactors (D37 and D38), and L33.

Often in cases like this (when one cannot induce the failure to
troubleshoot), it is quicker and easier just to make an educated guess
and replace most everything associated with that circuit - that thinking
often is better than the frustration that results from trying one
component at a time.

73,
Don W3FPR

W B Reese wrote:

> Dear Elecrafters,
>
> For some years now my K2/100 S/N 838 has had an intermitt.
>
> When I take it to a new location, it is generally jostled somewhat in
> moving it and hooking it up.
>
> When all installed, everything works perfectly,... then...
>
> Without warning, the received tone on the other guy gets "holes" in
> it.  Like a noise blanker is cutting out the audio on noise bursts,
> only the noise blanker is off and these holes are much bigger than
> noise blanker holes.  The holes get bigger and bigger until you can't
> read the other station, then, mysteriously, they go away and all is
> normal.  If you are transmitting during one of these episodes, the
> other station will report that you are breaking up.
>
> Whatever it is, affects both transmitt and receive the same.
>
> Some years ago I discovered that unplugging the anderson power
> connector on the rear and plugging it back in cleared the problem,
> but it troubled me that this is not a very good way to turn
> transistors on and off and it could result in transients.  It
> certainly made a loud "pop" in the loudspeaker.  Obviously, there was
> a problem in the power cord !  So the cord was replaced and the VCC
> was measured during a breaking up episode and found to be stable
> inside the K2/100.  So it was not the power cord.
>
> The next solution was to turn K2 on it's left side and hit it with a
> good smart "whack" with my fist.  After one or two of these, the
> problem clears and does not come back until K2 is taken on a trip,
> and then it starts up again.
>
> An "easy fix" and much less potentially destructive than jerking the
> power cord in and out.  Never the less, still embarrassing on field
> day when I'm out with the "boys."
>
> Does anyone have an idea what might be causing this ?
>
> Thanks,
>
> TR, WB6TMY
> K2/100 S/N 838
>  
>

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