[Elecraft] K2 PLL reference oscillator problems (DAC side!)

[Dave Van Wallaghen]

Chris,

I have worked on a few late model K2'S of late with the exact same problem. 
The folks in support are currently looking into it to determine the source 
of the problem.

My solution was to replace the Control board EEPROM with a known properly 
initialized one and everything came back to life. I even discussed this 
with Wayne in Dayton. We're looking into whether we have an EEPROM issue or 
a possible programming anomaly with the main PIC MCU.

I'm currently on vacation with my wife 8 miles off the coast of Belize. I 
have limited WIFI but will continue to check in.

Stay tuned...


73,
Dave, W8FGU
On May 21, 2019 10:28:00 "Chris Smith" <me at m0xte.uk> wrote:

> Hi,
>
> I've just completed my K2 up to the PLL reference oscillator.
>
> Initially when I assembled it the PLL reference oscillator would not 
> oscillate at all. No reading on internal counter. I popped it on my 
> external Racal counter and still dead. After tracing the problem out I 
> found that the voltage on input to the varactors was pegged at 7.07V which 
> was too high for the oscillation to carry on. I lifted one end of R19 on 
> the output of U6A and the thing oscillates fine isolating this to a control 
> voltage problem.
>
> Next I checked voltages on the thermistor board and input of the opamp. All 
> good. However the input to U6A pin 3 from the LTC1451 DAC is stuck at 
> 4.095V (top end of DAC range by the looks of it) which is forced up by the 
> opamp. Popped U5 DIN on the scope and spun the VFO and it sends the same 
> data word to the DAC every time regardless of VFO position. The CLK and CS 
> lines are doing their thing correctly.
>
> Anyone got any ideas why the control word is the same? VFO reading on 
> display is changing fine.
>
> What can I do to get out of this hole?
>
> Any help appreciated.
>
> Best regards,
>
> Chris M0XTE
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