[Elecraft] K2 #2740 13 Khz Off Freq UPDATE

Sun Aug 18 22:40:02 2002

I have incorrectly labeled the VCO.

It is actually the PLL Reference oscillator.... X1 & X2, U5, U6A, and Q19
(and associated components)

Sorry for the confusion.

73
Jim W7RY

----- Original Message -----
From: "Jim W7RY" <[email protected]>
To: <[email protected]>
Cc: <[email protected]>
Sent: Sunday, August 18, 2002 7:26 PM
Subject: Re: [Elecraft] K2 #2740 13 Khz Off Frequency

> Well here are more details on my problem with the K2. (VFO reads 13KHz
> higher that actual frequency and images at 1 KHz below)
>
> Measured the DC voltage at pin 1 of U6 on the RF board.
>
> It DOES move smoothly except for 1 instance....
>
> When I use the CAL FCTR and measure TP-3, the frequency changes between
> 12.087.00 MHz (pin 1 measures 1.6 volts) and 12082.40 (pin 1 measures .44
> volts).
>
> The anomaly comes when the VCO frequency reads 12.102.39 MHz, the voltage
is
> 7.17 volts! This reading occurs only within about a 200 Hz change of the
VFO
> knob! ALSO, when the VCO voltage is 7.17 volts and the VCO frequency is
> 12.102.39 MHz, the K2 is within about 1 KHz of being on frequency.
>
> I have checked all of the components for the proper marked value around
the
> VCO circuit. All check out fine. I have also checked the Vcc on both U5
and
> U6.
>
> If I had to guess, I would say that the microprocessor is telling the A/D
> converter to work this way. Small possibility that U5 is defective.
>
> I have also checked for solder bridges on the control board and have found
> none. (This is not my first kit !! ) I have been soldering circuit boards
> for 27+ years. ( I do however make mistakes :)  )
>
> What do you think ??
>
> 73 and thanks
> Jim W7RY
>
>
>
>
> ----- Original Message -----
> From: "Jim W7RY" <[email protected]>
> To: <[email protected]>
> Sent: Friday, August 16, 2002 7:21 PM
> Subject: [Elecraft] K2 #2740 13 Khz Off Frequency
>
>
> > Well... I have # 2740 running as a 40 meter receiver... But, it receives
> > exactly 13Khz off frequency (VFO reads high).
> >
> > There is another peculiar thing.... at 11.5 KHz above the injected
> > frequency, there is a "birdie". The birdie moves much faster than the
> > fundamental at +13 KHz above.
> >
> > I have verified that all of the crystals AS SUPPLIED are installed in
the
> > correct locations...
> >
> > I have also verified that the 4.00 MHz reference is within 1 or 2 Hz.
> >
> > All of the checks and alignments that are shown in "Alignment and Test
> Part
> > II" starting on page 57 are correct and line up perfectly.
> >
> > The parts list spells out  X1 and X2 to be a 12.069 MHz. My kit
contained
> > crystals that are marked  12.09-S.
> > In addition, X5 through X11 are marked 4.9136-S.
> >
> >
> > The receiver works great! Very sensitive.
> > The signal I am injecting is at a level of -105dBm. (Not overloading the
> > receiver).
> >
> > Any ideas ?
> >
> > Thanks and 73
> > Jim W7RY
> >
> >
> >
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> >
> >
>
>
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