K2 Tuning problem

[Mike Stunes]

My K2, #5943, is having a bit of an issue. I've just finished the last
construction stage (except for final assembly) and have yet to do the
final alignment. The issue is, I've got a problem somewhere around U6 on
the RF board. During CAL PLL, its input from U5 decreases steadily in
voltage, as it should, except its output remains at a constant 8 VDC.
During normal use, the VFO display acts normal but I can effectively
only tune in approx. 5 KHz intervals, due to how the K2's fine tuning
works. Examining the board did not show any shorts anywhere around U6 or
on the thermistor board. Any ideas?
--
73, Mike
KCØTQX
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[Don Wilhelm-3]

Mike,

You most likely do have a thermistor board problem - a short from pin 2(and
3) to ground (pins 4 and 5) could cause the situation you describe - in that
case, the op amp would be producing full output with any voltage input above
zero volts.

73,
Don W3FPR

> -----Original Message-----
>
> My K2, #5943, is having a bit of an issue. I've just finished the last
> construction stage (except for final assembly) and have yet to do the
> final alignment. The issue is, I've got a problem somewhere around U6 on
> the RF board. During CAL PLL, its input from U5 decreases steadily in
> voltage, as it should, except its output remains at a constant 8 VDC.
> During normal use, the VFO display acts normal but I can effectively
> only tune in approx. 5 KHz intervals, due to how the K2's fine tuning
> works. Examining the board did not show any shorts anywhere around U6 or
> on the thermistor board. Any ideas?
> --
> 73, Mike
> KCØTQX
>

--
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[Ken Kopp-2]

I had not soldered the common junction of two resistors ... (:-))

73! Ken Kopp - K0PP
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[Chuck-51]

Mike,

I'm sure Don and Ken are steering you right.  Visual inspection of the thermistor board may not be enough.  I had a problem there myself, signed off on it as good several times and went looking elsewhere for the problem.  

Finnally, after quit a bit of disassembly, I reflowed what looked like a good solder joint and my K2 took off playing just like it should.

Spend some time there and I'm sure you will find the culprit.

73,

Chuck K4QS



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[Don Wilhelm-3]

That says that you have a problem with either the thermistor board (your
previous email indicted thatyou did not), or in the path from the U6 pin 1
output to the varistors.  Check  the soldering on R19 and those components
that are near it (check the schematic to find the other connected
components).

73,
Don W3FPR


> -----Original Message-----

> Don Wilhelm wrote:
> > Mike,
> >
> > OK, it appears as though the output and input of U6A is correct
> (at least at
> > the extreme ends).
> > If your PLL range was correct (recheck frequencies at TP3), then CAL PLL
> > should run fine.
> >
> > When CAL PLL starts, the frequency displayed should be near
> 12100 kHz and
> > count downward from there - the process takes about 8 minutes.
> >
> Frequency displayed initially is OK, but it doesn't really change at
> all. U6p3 decreases steadily (as it should) but p1 is fixed at
> about 8 VDC.
>
>
> --
> Immanuel Kant but Kubla Khan.
>
> 73, Mike
> KCØTQX
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.5.446 / Virus Database: 268.18.4/705 - Release Date:
> 2/27/2007 3:24 PM
>

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