strange tuning effect on k2

[pc5m, Carel]

Hi,  busy building a k2 and have following problem:
 
- Alignment and test part II
 
Performed this alignment (a.o. VCO alignment and VFO linearization),
everthing went well, but:
 
It turned out that that when tuning the frequency the tuning is very
strange, no 10 Hz steps but rather erratic but after every 5-10 KHz it goes
ok. Display gives the idea everything is ok (moves very smoothly) but when
listening with a seperate receiver to the internal RX vfo it is not smooth.
 
Measuring the PLL reference frequency Xtal VCXO: not smooth
Measuring the PLL reference voltage out of the DAC: voltage is jumping !
 
Strange is when I perform the VFO linearization the DAC voltage is very
smooth progressing and also the PLL reference is moving very smoothly. VFO
linearization ends with "end" no error.
 
Anybody an idea what is going wrong ?
 
thanks,
 
Carel, pc5m
 
 
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[pc5m, Carel]

Hi Bob and others who have replied to me (Thanks!)
 
Checked the choke RFC15= ok. I do have 5V on both sides of the choke.
 
One strange behaviour is that when I perform PLL lin. I set the K2 to 7.050
MHz . But when I perform the PLL lin. (by connecting to TP1 and measuring
the VFO freq) it goes to 12.094 MHz, which is 12.094-4.9136 = 7.1804 MHz. So
NOT the 7.050 MHz ! Is that normal behaviour ?
 
I can see that during the PLL lin. the VFO freq drops very smoothly from
12.094 to 12.085 (verified that with an external receiver on 12 MHz) and the
PLL lin. stops with an "end" message.
 
But stil when tuning, the 10Hz steps are not there !. Voltage on D16/D17 and
also the DAC U5 output  goes wild when turning slowly the freq. knob. On the
other hand the VFO voltage (at R30) is very smooth and well in normal range.
So it seems the DAC is programmed with rather erratic data....could it be I
have a defect EEPROM ? (it stores ok other things like S-meter Low/High
though...)
 
Thanks in advance,
 
Carel.

  _____  

From: [hidden email] [mailto:[hidden email]]
Sent: Friday, June 10, 2005 1:04 AM
To: [hidden email]
Subject: Re: [Elecraft] strange tuning effect on k2


Hi Carel,
 
As a start check that the 100uH  choke RFC15 that feeds the 5V supply into
the PLL chip U4 pin 16 is not open circuit. Very easily damaged and gives
some odd effects when broken.
 
Regards,
Bob, G3VVT
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[Don Wilhelm-3]

Carel,

Check the choke RFC15 with an ohmmeter - the voltage check will not suffice.
I haven't investigated why, but the PLL chip shows 5 volts on the pin the
choke is connected to even when the choke is open.

When doing CAL PLL, the frequency count starts from the PLL high frequency
value (seen in CAL FCTR mode after tapping BAND+) and does not depend on any
particular frequency within the 40 meter band.

If RFC15 is open, you can replace it with a jumper until a replacement is
obtained.

73,
Don W3FPR

> -----Original Message-----
>
> Checked the choke RFC15= ok. I do have 5V on both sides of the choke.
>
> One strange behaviour is that when I perform PLL lin. I set the
> K2 to 7.050
> MHz . But when I perform the PLL lin. (by connecting to TP1 and measuring
> the VFO freq) it goes to 12.094 MHz, which is 12.094-4.9136 =
> 7.1804 MHz. So
> NOT the 7.050 MHz ! Is that normal behaviour ?
>
> I can see that during the PLL lin. the VFO freq drops very smoothly from
> 12.094 to 12.085 (verified that with an external receiver on 12
> MHz) and the
> PLL lin. stops with an "end" message.
>
> But stil when tuning, the 10Hz steps are not there !. Voltage on
> D16/D17 and
> also the DAC U5 output  goes wild when turning slowly the freq.
> knob. On the
> other hand the VFO voltage (at R30) is very smooth and well in
> normal range.
> So it seems the DAC is programmed with rather erratic
> data....could it be I
> have a defect EEPROM ? (it stores ok other things like S-meter Low/High
> though...)
>
>

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