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K-2 Part II test and alignment problem

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Larry Wright

K-2 Part II test and alignment problem

Hi All,

I am at the Alignment and Test Part II.

Minor problems with direct freq entry were resolved by resoldering connections, but having difficulty described below.

PLL Reference Osc Range Test yields 12.099 - 12.086 = 13 Khz range. But the VCO Test yields 5.535 Mhz instead of the expected 10 to 12 Mhz reading.

The K-2 receives every 5 Khz . The problem seems to me to involve the 12 Bit DAC (U5). Have resoldered the pins to it. Pin 8 is 5v, but pin 7 stays at 3.4v at all times. Pin 1 on U6 stays at 7.6v. (the 8v Regulator output is 7.6v) The 7.6v output is present to the PLL ref. osc circuit. Turning the dial has no effect on the output of the DAC. The PLL Reference osc stays at 12.099 Mhz.

BFO appears to be working fine. Sensitivity appears good as I can easily hear a 1 uv signal.

I have thought of putting say, a 5 K resistor across the output of pin 1 (or from the 2.7K R19 to ground) on U6 to change the 7.6v to something lower to see if that changes anything, but not have not tried that yet. I'm trying to think of a way to test the 12 Bit DAC to see if it is good.

Any suggestions or help will be greatly appreciated.

Larry

N4QY

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David Woolley (E.L)

Re: K-2 Part II test and alignment problem

Larry Wright wrote:
>
>
> PLL Reference Osc Range Test yields 12.099 - 12.086 = 13 Khz range.
> But the VCO Test yields 5.535 Mhz instead of the expected 10 to 12 Mhz
> reading.

That suggests a band switching problem, or problems with the VCO band
range capacitors or varicaps. Could you possibly have spun the dial to
get on band, rather than used the bandswitches. If so, you may need to
do a direct frequency entry.

>
> The K-2 receives every 5 Khz . The problem seems to me to involve the

What do you maan by that (although it may be a symptom of not having
calibrated the reference oscillator)?

> 12 Bit DAC (U5). Have resoldered the pins to it. Pin 8 is 5v, but
> pin 7 stays at 3.4v at all times. Pin 1 on U6 stays at 7.6v. (the 8v
> Regulator output is 7.6v) The 7.6v output is present to the PLL ref.
> osc circuit. Turning the dial has no effect on the output of the DAC.
> The PLL Reference osc stays at 12.099 Mhz.

But you previously said that the reference oscillator range check
passed, which indicates that control voltage is being varied. I think
this symptom arises from a failure to calibrate.

--
David Woolley
"The Elecraft list is a forum for the discussion of topics related to
Elecraft products and more general topics related ham radio"
List Guidelines <http://www.elecraft.com/elecraft_list_guidelines.htm>
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Don Wilhelm-4

Re: K-2 Part II test and alignment problem

In reply to this post by Larry Wright

Larry,

Have you run the CAL PLL routine from the menu yet? If not, you do not
have valid data in the EEPROM and that prevents tuning.

If you wish to check the DAC, monitor the voltage at U5 pin 7 while the
menu is set to CAL FCTR - when you tap the BAND+ button, the voltage
should go to about 4 volts, and when you tap the BAND- button it should
go near zero volts. If that check passes, the DAC is capable of
working, so run CAL PLL and see if the K2 tunes afterward.

Having done that, you can then check the VCO voltages at R30 and check
the VCO frequencies. If either of these are incorrect, check the
capacitors and varactors in the VFO Range Select area.

73,
Don W3FPR

Larry Wright wrote:

> Hi All,
>
> I am at the Alignment and Test Part II.
>
> Minor problems with direct freq entry were resolved by resoldering
> connections, but having difficulty described below.
>
> PLL Reference Osc Range Test yields 12.099 - 12.086 = 13 Khz range.
> But the VCO Test yields 5.535 Mhz instead of the expected 10 to 12
> Mhz reading.
>
> The K-2 receives every 5 Khz . The problem seems to me to involve
> the 12 Bit DAC (U5). Have resoldered the pins to it. Pin 8 is 5v,
> but pin 7 stays at 3.4v at all times. Pin 1 on U6 stays at
> 7.6v. (the 8v Regulator output is 7.6v) The 7.6v output is present
> to the PLL ref. osc circuit. Turning the dial has no effect on the
> output of the DAC. The PLL Reference osc stays at 12.099 Mhz.
>
> BFO appears to be working fine. Sensitivity appears good as I can
> easily hear a 1 uv signal.
>
> I have thought of putting say, a 5 K resistor across the output of pin
> 1 (or from the 2.7K R19 to ground) on U6 to change the 7.6v to
> something lower to see if that changes anything, but not have not
> tried that yet. I'm trying to think of a way to test the 12 Bit DAC
> to see if it is good.
>
> Any suggestions or help will be greatly appreciated.
>
> Larry
> N4QY
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