K-1 VFO range jump

My K-1 quit (no TX, no RX) a few months ago and am just now getting
around to working on it.

It is a 2-band kit with 20 and 40 installed.

Originally set up for 7.000-@7.060; 14.000-@14.060.

I removed and replaced the filter board.  RX, TX fine except the
range is now 14.047.3 - 14.075.1 and 7.053.6 - 7.081.3.

Spread the turns of L1 and could get to go as low as 7.0361 and as high as 7.0640.  

These frequencies agree with a good receiver and a good signal source.

I'm reluctant to snip off a turn from L1 since it worked fine before
with the current number of turns.

A concern is the lack of tuning range.

VFO OSC is 3.027 - 3.055.

I'd be grateful for advice.

72,

Tim Colbert  K3HX

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[Don Wilhelm-4]

Tim,

You certainly are correct in not jumping to conclusions about the need
to just change the winding of L1 - that will not alter the tuning range,
but will simply shift the frequency at the beginning of the range.

First check is the voltage on the VFOPOT signal line which can be
observed at the RF Board connector P1 (to the front panel) pin 14. Move
the VFO knob from one end to another - the voltage should change
gradually from 0 volts at one end to near 8 volts at the other end.  If
it does not, there is something wrong with the VFO pot or the
connections to it.

If you do get the expected voltage range, check for the same voltage
range at the cathode of D3 (or pin 2 of RP2 (both should be the same
because they are connected).

If all is well so far, then suspect that the problem has to do with
soldering.  Reflow the soldering at C2, D3, RP2 and possibly other
points with a hot iron (750 degF).

73,
Don W3FPR


On 6/24/2012 5:32 PM, [hidden email] wrote:

> My K-1 quit (no TX, no RX) a few months ago and am just now getting
> around to working on it.
>
> It is a 2-band kit with 20 and 40 installed.
>
> Originally set up for 7.000-@7.060; 14.000-@14.060.
>
> I removed and replaced the filter board.  RX, TX fine except the
> range is now 14.047.3 - 14.075.1 and 7.053.6 - 7.081.3.
>
> Spread the turns of L1 and could get to go as low as 7.0361 and as high as 7.0640.
>
> These frequencies agree with a good receiver and a good signal source.
>
> I'm reluctant to snip off a turn from L1 since it worked fine before
> with the current number of turns.
>
> A concern is the lack of tuning range.
>
> VFO OSC is 3.027 - 3.055.
>
>

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[Mike Morrow-3]

> My K-1 quit (no TX, no RX)...
>
> Originally set up for 7.000-@7.060; 14.000-@14.060.

That's a little unusual...with the standard narrow VFO span
option for RF-C2 of 82 pf the K1 will typically tune from
about xx.000 to xx.085 or so.

> I removed and replaced the filter board.  RX, TX fine
> except the range is now 14.047.3 - 14.075.1 and
> 7.053.6 - 7.081.3.

Was *anything* shown on the LCD back when the K1 was not
working at all?

> Spread the turns of L1 and could get to go as low as
> 7.0361 and as high as 7.0640.  
>
> I'm reluctant to snip off a turn from L1 since it worked
> fine before with the current number of turns.

Absolutely do NOT do anything to L1.  You did not need to
adjust turn spacing...but you will after you fix the
problem to get it back to where it should be.

Find the two terminals of the VFO pot that have FP-R19 100k soldered to them.

Rotate the VFO pot to full CCW position.

Measure the voltage from each of these terminals to
ground (the screw anchor blocks for the cover work well).

You *should* find 5.9 to 6.0 volts at each point.

Next, turn on RIT and report how much the LCD frequency
changes from full CCW to full CW.  This should be about
8 kHz (+/- 4 kHz around center frequency).

I suspect that there may be a problem with the 6V VFO
regulator RF-U6 (ZR78L06C) and what you observe above
can help determine that.

The actual output frequency of your VFO should be about
3090 kHz (VFO pot full CCW) to 3005 kHz (VFO pot full CW).

73,
Mike / KK5F
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