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

[Don Wilhelm]

Chris,

If it is a EEPROM data problem, then a Master Reset should load it with 
default values - hold the 4, 5, and 6 buttons in while turning power on.

I have not found that the EEPROM has been the source of the problem, but 
rather Q19.
Q19 should oscillate with anywhere between 0 volts and 8 volts on the 
varactors.

Before assuming it is a possible EEPROM problem, add the capacitor I 
indicated and see if it works.  You should still replace Q19.

To further check the EEPROM and U5 DAC

On 5/21/2019 1:21 PM, Chris Smith wrote:
> Hi,
> 
> Thanks for the reply. Much appreciated.
> 
> That’s a bummer. Is there anything I can do here with the current EEPROM? I have a programmer available. I assuming erasing it and letting the K2 reinitialise it a small per earlier steps won’t resolve this?
> 
> Based on looking at it from the outside naively, it feels like theres something up with the VCO linearisation as it’s sending the control word on VFO steps but the same data. I’ll get a bus captures if it helps.
> 
> Assume that performing the VCO linearisation steps later won’t fix it either?
> 
> Hope you enjoy your vacation - sounds nice!
> 
> Best regards,
> 
> Chris M0XTE
> 
> On Tue, 21 May 2019, at 18:11, Dave Van Wallaghen wrote:
>> 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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