[K1] Tuning Jump Cause

[Curt]

My K1 has developed a glitch.  Sometimes, while tuning, the displayed
frequency will suddenly jump down about 10-15 kHz, then return to the
correct frequency.  I hear some static in the headphones at the same time.
The jump isn't caused by tapping the case, only moving the tuning knob.  It
doesn't seem related to a specific "spot" on the pot.  Without rotating the
tuning pot, there is no frequency instability at all.

Ideas?  Curt KB5JO

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[Mike Morrow-3]

> My K1 has developed a glitch.  Sometimes, while tuning, the
> displayed frequency will suddenly jump down about 10-15 kHz,
> then return to the correct frequency...
> The jump isn't caused by tapping the case, only moving the
> tuning knob.

Check the solder connections on both ends of the leads going
from the VFO pot to the front panel board.  In particular,
check the solder connections of R19 that is soldered to two
terminals of the VFO pot.  If you move these components
slightly while watching the LCD for erratic response you may
be able to find the exact problem source.

73,
Mike / KK5F
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[Don Wilhelm-4]

Curt,

Behavior like that is almost always associated with a bad connection.
Check the soldering at the tuning pot.  If it is an older K1, there is a
great possibility that the VFO pot could be worn enough to cause that
behavior.

73,
Don W3FPR

On 6/22/2012 8:05 AM, Curt wrote:
> My K1 has developed a glitch.  Sometimes, while tuning, the displayed
> frequency will suddenly jump down about 10-15 kHz, then return to the
> correct frequency.  I hear some static in the headphones at the same time.
> The jump isn't caused by tapping the case, only moving the tuning knob.  It
> doesn't seem related to a specific "spot" on the pot.  Without rotating the
> tuning pot, there is no frequency instability at all.
>
>

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[Curt]

My K1 is S/N 2258, don't remember when I built it but believe around 2007. Would the pot wear out in 5 years? The rig isn't used that often and nearly always inside.  It has always been in air conditioned and dry conditions.
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[Curt]

I notice the tuning pot seems to have more play than would have thought appropriate, can't say if this has increased.  The "jump" happens at several particular frequencies on all bands.  For example, 7055, 7130; 14055, 14130. Manipulating connections inside the case from the port to the board has no effect. Jaring the rig has no effect.  The "jump" seems to only happen while tuning down the band.  Pushing and pulling the tuning knob sometimes causes a "jump".  I'm leaning toward replacing the Bourne pot, maybe the wiper has developed a problem. Is there potential for any rebate from Bourne?

Thoughts?  Curt KB5JO
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[Don Wilhelm-4]

Curt,

OK, that is information that I did not have initially, so I only
mentioned the possibility - my ISP is broken :-) ..
Given that new information, I would suggest you look for a faulty solder
connection.  Re-flow the soldering around the VFO pot with a hot (750
degF) soldering iron.

73,
Don W3FPR

On 6/22/2012 8:14 PM, [hidden email] wrote:
> My K1 is S/N 2258, don't remember when I built it but believe around 2007. Would the pot wear out in 5 years? The rig isn't used that often and nearly always inside.  It has always been in air conditioned and dry conditions.
>

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[Mike Morrow-3]

> The "jump" happens at several particular frequencies on all
> bands.  For example, 7055, 7130; 14055, 14130. Manipulating
> connections inside the case from the port to the board has no
> effect. Jaring the rig has no effect.  The "jump" seems to
> only happen while tuning down the band.  Pushing and pulling
> the tuning knob sometimes causes a "jump".  I'm leaning
> toward replacing the Bourne pot, maybe the wiper has
> developed a problem.

If the pot has the problem at specific positions of the wiper
then the frequencies shown on each band for the troublesome
position should vary for each band by the amount that each
band varies as shown at the full CCW position.  For example,
My K1 displays 98.1 on 40m and 92.1 on 20m.  If my pot
shows a problem at 7040, I should see that also at 14034.
This variance occurs from the heterodyne crystals not being
exactly on their nominal frequency.

But I tend to agree that it looks like the pot is suspect
based on all you report.  Early pot failures have been
reported especially after an impact that pushes the knob
into the panel.  Sometimes even the back of the pot has
separated.

> Is there potential for any rebate from Bourne?

It's good that you've retained your sense of humor!

73,
Mike / KK5F
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