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K2 PLL range test fails

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Mike Maiorana-2

K2 PLL range test fails

Since fixing my BFO range issue I started going through a full alignment. I
roughly set the BFO for all the filters. I noticed my frequency display was
off about 1500 Hz, so I re-set the 4MHz oscillator, then tried to run CAL
PLL. The CAL PLL started, but never finished. It just sat right around
12.1MHz.

I went back and tried the "PLL Reference Oscillator Range Test", which had
passed the first time I went through calibration. Now, it is "stuck" on
12.097MHz. What is strange is that it will jump briefly when I press Band+
and Band-, but it settles back to 12.097MHz.

I put a volt meter on pin 1 of U6 on the RF board to check the control
voltage. When I press Band- I can see the voltage briefly drop to near
zero. When I press Band+ it jumps to 7.5V or so, then goes back to the
original value.

If I rotate the VFO knob I can see the PLL frequency and the control
voltage vary over a range of about 5kHz on the VFO.

It seems that the PLL is moving with the control voltage, but the Band+ and
Band- keys during Cal FCTR don't seem to be doing what they should. Is it
possible that I fouled up another part of the calibration that is causing
this weird behavior? It sure feels like I'm doing something wrong, but I
can't figure it out.

I did a factory reset (hold 4,5,6 and power on), but I'm still seeing the
same issue with the PLL.

Any help will be greatly appreciated.

Thanks and 73
Mike M.
KU4QO
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Don Wilhelm

Re: K2 PLL range test fails

Mike,

Record your current filter settings and other menu settings, and then do
a Master Reset (hold the 4, 5 and 6 buttons in while powering on).

There is a convenient form to record the menu settings in the K2 A to B
instructions which you can download from the Elecraft website.

You may have to replace the firmware (to be determined later), but
perhaps RF board U7 is not receiving as it should. If you have a
'scope, you should be able to see pulses on U7 pins 1, 2, and 3 as you
rotate the VFO knob. If all 3 pins show pulses, then most likely U7 is
not working properly. U7 pin 7 should move from 5 volts to zero volts
in CAL FCTR when you tap the BAND+ and BAND- buttons. If it does, then
U7 is operating correctly.

Also make a quick check on the Thermistor board - a quick check is to
measure the voltage at U5 pin 5 - it should be 4 volts or 1/2 the 8 volt
supply. If not, check the Thermistor board for solder bridges. You can
see the back of the Thermistor board if you remove the Control Board and
Front Panel.

73,
Don W3FPR

On 10/15/2017 10:02 PM, Mike Maiorana wrote:

> Since fixing my BFO range issue I started going through a full alignment. I
> roughly set the BFO for all the filters. I noticed my frequency display was
> off about 1500 Hz, so I re-set the 4MHz oscillator, then tried to run CAL
> PLL. The CAL PLL started, but never finished. It just sat right around
> 12.1MHz.
>
> I went back and tried the "PLL Reference Oscillator Range Test", which had
> passed the first time I went through calibration. Now, it is "stuck" on
> 12.097MHz. What is strange is that it will jump briefly when I press Band+
> and Band-, but it settles back to 12.097MHz.

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Mike Maiorana-2

Re: K2 PLL range test fails

Thanks again Don. This was an interesting one.

The DAC was constantly receiving data/clock signals from the CPU, even with
all the controls at rest. You could see the DAC output voltage jump when
the Band+ or Band- keys were pressed while in CAL FCTR, but then went
immediately back to where it started. I was stumped.

A little "googling" turned up an old post from 2004 by John G3NYX who had
the same problem while building his K2. Someone suggested to him to move
the RIT control and try again. Now, I confirmed that my RIT wasn't on so I
figured that it would have nothing to do with this issue. I was wrong. I
twisted the RIT knob a few times back and forth and then retested the PLL
range. Now everything works! It seems that even with RIT off, the CPU still
sends data to the DAC because of RIT. If the RIT control was a little noisy
and was right in between two readings it would cause the CPU to constantly
update the PLL reference oscillator DAC.

CAL PLL worked great, the BFO adjustments are done and the radio is working
great now.
Thanks for your help Don!
Mike M.
KU4QO

On Mon, Oct 16, 2017 at 8:11 AM, Don Wilhelm <[hidden email]> wrote:

> Mike,
>
> Record your current filter settings and other menu settings, and then do
> a Master Reset (hold the 4, 5 and 6 buttons in while powering on).
>
> There is a convenient form to record the menu settings in the K2 A to B
> instructions which you can download from the Elecraft website.
>
> You may have to replace the firmware (to be determined later), but perhaps
> RF board U7 is not receiving as it should. If you have a 'scope, you
> should be able to see pulses on U7 pins 1, 2, and 3 as you rotate the VFO
> knob. If all 3 pins show pulses, then most likely U7 is not working
> properly. U7 pin 7 should move from 5 volts to zero volts in CAL FCTR when
> you tap the BAND+ and BAND- buttons. If it does, then U7 is operating
> correctly.
>
> Also make a quick check on the Thermistor board - a quick check is to
> measure the voltage at U5 pin 5 - it should be 4 volts or 1/2 the 8 volt
> supply. If not, check the Thermistor board for solder bridges. You can
> see the back of the Thermistor board if you remove the Control Board and
> Front Panel.
>
> 73,
> Don W3FPR
>
>
>
>
> On 10/15/2017 10:02 PM, Mike Maiorana wrote:
>
>> Since fixing my BFO range issue I started going through a full alignment.
>> I
>> roughly set the BFO for all the filters. I noticed my frequency display
>> was
>> off about 1500 Hz, so I re-set the 4MHz oscillator, then tried to run CAL
>> PLL. The CAL PLL started, but never finished. It just sat right around
>> 12.1MHz.
>>
>> I went back and tried the "PLL Reference Oscillator Range Test", which had
>> passed the first time I went through calibration. Now, it is "stuck" on
>> 12.097MHz. What is strange is that it will jump briefly when I press Band+
>> and Band-, but it settles back to 12.097MHz.
>>
>