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K2.Unable to undertake VCO alignment.

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M Bak

K2.Unable to undertake VCO alignment.

Issue. Unable to undertake VCO alignment. Voltage at R30 fixed at 24mV.

The VCO oscillator test (Alignment and test Part II p 63) has passed. Well
the frequency is 7.98MHz rather than 8->10 but that conceivably could be
within the bounds of measurement error.

In the VCO alignment test a DMM (Keysight U1271) clamped onto the left side
end of R30 reads 24mV no matter what the setting of L30.

I have looked everywhere over the appropriate circuitry but can see no
issues. Including triple checking T5 which is 100% wound and fitted
properly.

I made the measurements from troubleshooting (PLL Reference Oscillator and
VCO P 10) and got:-

Reference Oscillator Output 0.72

VCO Output 0.24

VCO Buffer Output 0.59

All measurements are at the low end of the acceptable range but just in
spec.

I measured voltages in the area and have noted the following:-

1. U4 (MC145170) pin 7 CLK/SCK is at 5v as against the specified 0v.

2. U4 pin 13 PDOUT is at 5v rather than 4v. This feeds the inverting
input of U6B causing the output to be low.

3. The gate input of Q18 is 0 rather than -1.

I am at a loss as to what to check next and any suggestions would be most
welcome. BTW I also have a ½ decent scope so can probe with that assuming I
can figure out what I should be seeing. The K2 is a brilliant kit but
seriously different to tube amps. which is my usual playpen.

Thanks
--
If you are afraid you are living in the future. If you are sad you are
living in the past. If you are content you are living in the now.
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Elecraft mailing list

Re: K2.Unable to undertake VCO alignment.

I am suffering from a similar problem in the midst of applying the various upgrades. My BFO test numbers are good,
4917.13 kHz
4912.16 kHz
4.97 kHz range

but when I try the VCO linearization process, I see 11090 flash and then get error 232. I have not checked the VFO against a reference frequency. I have tried two different crystals and several different L31 values.

My planned next step is to assemble the RF probe and see if I can figure out what is going on.

Doug, W0UHU.

> From: M Bak <[hidden email] <mailto:[hidden email]>>
>
> Issue. Unable to undertake VCO alignment.

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Don Wilhelm

Re: K2.Unable to undertake VCO alignment.

In reply to this post by M Bak

What were the results of the PLL Reference Oscillator test - especially
the high frequency at TP3? - the frequencies please.

The 5 volts on the SCK signal is normal.

Do not wear out the slug in L30!

Is this a new build or the result of upgrades to an old K2?
Do you have an oscilloscope with a 10X probe?

73,
Don W3FPR

On 1/27/2021 6:59 AM, M Bak wrote:

> Issue. Unable to undertake VCO alignment. Voltage at R30 fixed at 24mV.
>
>
>
> The VCO oscillator test (Alignment and test Part II p 63) has passed. Well
> the frequency is 7.98MHz rather than 8->10 but that conceivably could be
> within the bounds of measurement error.
>
>
>
> In the VCO alignment test a DMM (Keysight U1271) clamped onto the left side
> end of R30 reads 24mV no matter what the setting of L30.
>
>
>
> I have looked everywhere over the appropriate circuitry but can see no
> issues. Including triple checking T5 which is 100% wound and fitted
> properly.
>
>
>
> I made the measurements from troubleshooting (PLL Reference Oscillator and
> VCO P 10) and got:-
>
>
>
> Reference Oscillator Output 0.72
>
> VCO Output 0.24
>
> VCO Buffer Output 0.59
>
> All measurements are at the low end of the acceptable range but just in
> spec.
>
>
>
>
>
> I measured voltages in the area and have noted the following:-
>
>
>
> 1. U4 (MC145170) pin 7 CLK/SCK is at 5v as against the specified 0v.
>
> 2. U4 pin 13 PDOUT is at 5v rather than 4v. This feeds the inverting
> input of U6B causing the output to be low.
>
> 3. The gate input of Q18 is 0 rather than -1.
>
>
>
>
>
> I am at a loss as to what to check next and any suggestions would be most
> welcome. BTW I also have a ½ decent scope so can probe with that assuming I
> can figure out what I should be seeing. The K2 is a brilliant kit but
> seriously different to tube amps. which is my usual playpen.
>
>
> Thanks
>

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Don Wilhelm

Re: K2.Unable to undertake VCO alignment.

In reply to this post by Elecraft mailing list

Doug,

Are you on 40 meters?

Did you measure the PLL Reference oscillator range (counter probe in
TP3)? What were the frequencies?

Any chance you replaced Q19 during the upgrade process? If so, where
did you get it?

73,
Don W3FPR

On 1/27/2021 12:22 PM, Douglas Hagerman via Elecraft wrote:

> I am suffering from a similar problem in the midst of applying the various upgrades. My BFO test numbers are good,
> 4917.13 kHz
> 4912.16 kHz
> 4.97 kHz range
>
> but when I try the VCO linearization process, I see 11090 flash and then get error 232. I have not checked the VFO against a reference frequency. I have tried two different crystals and several different L31 values.
>
> My planned next step is to assemble the RF probe and see if I can figure out what is going on.
>
> Doug, W0UHU.
>
>> From: M Bak <[hidden email] <mailto:[hidden email]>>
>>
>> Issue. Unable to undertake VCO alignment.