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K2 Alignment and Test Part II: VCO Test fails

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Matthew Ellis

K2 Alignment and Test Part II: VCO Test fails

Hi,

I'm struggling to track down an issue with the VCO test in part 2 of the
alignment for my K2 (page 64 in my manual).

The 4MHz Oscillator calibration looks OK as the frequency on TP3 shows
as 12096hz stable (both on the internal test probe and an external freq
counter). The PLL test is in range as well. But I get nothing (0hz) on
TP1 for the VCO test with both the internal probe and a standalone
frequency meter.

I've checked and re-wound/re-fitted Transformer 5, gone over my assembly
with a magnifying glass a few times (both top and bottom side of the
pcb), confirmed all the components in the VCO area are present and
correctly oriented. I've also used a signal scanner on the i2c lines to
confirm the pll ic is getting the 'change freq' instructions. Most
voltages appear good compared to the manual, although the voltage on Q16
C and Q17 G is off (initially 8v then dropped to near 0v after i
re-soldered the joints of resistor R9). I have shorted C60 to
completely bypass the VFO ALC (suggestion from Elecraft).

All prior tests were fine, everything in expected range. Also the
correct frequency shows on pins 1 and 2 of U4 (MC145170), and voltages
look good on U3,4 & 6.

I'm in the UK, so sending it back to Elecraft is not my preferred option
(time/cost).

Has anyone got experience of issues in this area?

Thanks,

Matthew

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Don Wilhelm-4

Re: K2 Alignment and Test Part II: VCO Test fails

Matthew.

Zero Hz. says that Q18 is not oscillating.
To help you visualize a little better, forget about the PLL part and
concentrate on Q18 only. That is just a Hartley oscillator.

You have already shorted out the VFO ALC with the short across C60 - and
that is a good debugging step. The tuned circuit inductance consists of
L30 in parallel with the red winding of T5 and the capacitance is made
up of the varactors and capacitors switched in and out of the circuit by
K13, K14 and K15. That is really all there is to it as far as basic
oscillation is concerned.
Once it oscillates, then you can consider the other "appendages" like
the R30 voltage and the VFO ALC.

So, go over the circuit once again with that in mind. There is a reason
Q18 is not oscillating - Several possibilities: the green winding of
T5 is wound backwards, the diodes are oriented backwards, The varactors
are mounted backwards, Q18 is oriented incorrectly, Q18 is damaged,

Note also that the path to TP1 includes U3 (which also could be
failing). Since you have an external frequency counter, check for
oscillation at the source or Q18 rather than just at TP1.

You should first be trying to just get Q18 to oscillate. Once that is
working, the other parts come into play to make the frequency of
oscillation correct.

73,
Don W3FPR

On 7/15/2012 3:44 AM, Matthew Ellis wrote:

> Hi,
>
> I'm struggling to track down an issue with the VCO test in part 2 of the
> alignment for my K2 (page 64 in my manual).
>
> The 4MHz Oscillator calibration looks OK as the frequency on TP3 shows
> as 12096hz stable (both on the internal test probe and an external freq
> counter). The PLL test is in range as well. But I get nothing (0hz) on
> TP1 for the VCO test with both the internal probe and a standalone
> frequency meter.
>
> I've checked and re-wound/re-fitted Transformer 5, gone over my assembly
> with a magnifying glass a few times (both top and bottom side of the
> pcb), confirmed all the components in the VCO area are present and
> correctly oriented. I've also used a signal scanner on the i2c lines to
> confirm the pll ic is getting the 'change freq' instructions. Most
> voltages appear good compared to the manual, although the voltage on Q16
> C and Q17 G is off (initially 8v then dropped to near 0v after i
> re-soldered the joints of resistor R9). I have shorted C60 to
> completely bypass the VFO ALC (suggestion from Elecraft).
>
> All prior tests were fine, everything in expected range. Also the
> correct frequency shows on pins 1 and 2 of U4 (MC145170), and voltages
> look good on U3,4 & 6.
>
> I'm in the UK, so sending it back to Elecraft is not my preferred option
> (time/cost).
>
> Has anyone got experience of issues in this area?
>
> Thanks,
>
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html

Matthew Ellis

Re: K2 Alignment and Test Part II: VCO Test fails

Don,

Thanks to your pointing me in the right direction I appear to have
tracked down my issue: Capacitor R68 (10pf, next to K15) was duff
(probably damaged when I inserted it as the holes on the pcb are wider
than the lead spacing on the capacitor). The final clue was when I
broke an unrelated capacitor lead off which showed how easily they can
be damaged (I've put hundreds of capacitors into circuits without issue
before), The other clue was that when I touched my frequency meter
probe to TP1 I got a very brief reading before it dropped to zero, and
while it would continue to read zero if I touched tp1 repeatedly, if I
left it for a while (a minute or so) then touched the probe again, I
once again got a brief reading. This suggested to me that T5 was
probably OK (your telling me it was a Hartley oscillator helped there as
I then looked it up to get a better idea of the operation).

Lets hope it doesn't take me two weeks to get each of the various tests
to pass!

Thanks again,

Matthew

On 15/07/2012 14:14, Don Wilhelm wrote:

> Matthew.
>
> Zero Hz. says that Q18 is not oscillating.
> To help you visualize a little better, forget about the PLL part and
> concentrate on Q18 only. That is just a Hartley oscillator.
>
> You have already shorted out the VFO ALC with the short across C60 -
> and that is a good debugging step. The tuned circuit inductance
> consists of L30 in parallel with the red winding of T5 and the
> capacitance is made up of the varactors and capacitors switched in and
> out of the circuit by K13, K14 and K15. That is really all there is
> to it as far as basic oscillation is concerned.
> Once it oscillates, then you can consider the other "appendages" like
> the R30 voltage and the VFO ALC.
>
> So, go over the circuit once again with that in mind. There is a
> reason Q18 is not oscillating - Several possibilities: the green
> winding of T5 is wound backwards, the diodes are oriented backwards,
> The varactors are mounted backwards, Q18 is oriented incorrectly, Q18
> is damaged,
>
> Note also that the path to TP1 includes U3 (which also could be
> failing). Since you have an external frequency counter, check for
> oscillation at the source or Q18 rather than just at TP1.
>
> You should first be trying to just get Q18 to oscillate. Once that is
> working, the other parts come into play to make the frequency of
> oscillation correct.
>
> 73,
> Don W3FPR
>
>
>
> On 7/15/2012 3:44 AM, Matthew Ellis wrote:
>> Hi,
>>
>> I'm struggling to track down an issue with the VCO test in part 2 of the
>> alignment for my K2 (page 64 in my manual).
>>
>> The 4MHz Oscillator calibration looks OK as the frequency on TP3 shows
>> as 12096hz stable (both on the internal test probe and an external freq
>> counter). The PLL test is in range as well. But I get nothing (0hz) on
>> TP1 for the VCO test with both the internal probe and a standalone
>> frequency meter.
>>
>> I've checked and re-wound/re-fitted Transformer 5, gone over my assembly
>> with a magnifying glass a few times (both top and bottom side of the
>> pcb), confirmed all the components in the VCO area are present and
>> correctly oriented. I've also used a signal scanner on the i2c lines to
>> confirm the pll ic is getting the 'change freq' instructions. Most
>> voltages appear good compared to the manual, although the voltage on Q16
>> C and Q17 G is off (initially 8v then dropped to near 0v after i
>> re-soldered the joints of resistor R9). I have shorted C60 to
>> completely bypass the VFO ALC (suggestion from Elecraft).
>>
>> All prior tests were fine, everything in expected range. Also the
>> correct frequency shows on pins 1 and 2 of U4 (MC145170), and voltages
>> look good on U3,4 & 6.
>>
>> I'm in the UK, so sending it back to Elecraft is not my preferred option
>> (time/cost).
>>
>> Has anyone got experience of issues in this area?
>>
>> Thanks,
>>
>>
>

Don Wilhelm-4

Re: K2 Alignment and Test Part II: VCO Test fails

Matthew,

Great that you found the source of your problems. Onward and upward.

When you get all finished with your K2 and want to do a good dial
calibration, take a look at the K2 Dial Calibration article on my
website www.w3fpr.com and you should be able to get it "right on" with
that procedure. I do several every week, and I can tell you that the
method does work and works quite well.

73,
Don W3FPR

On 7/17/2012 3:35 PM, Matthew Ellis wrote:

> Don,
>
> Thanks to your pointing me in the right direction I appear to have
> tracked down my issue: Capacitor R68 (10pf, next to K15) was duff
> (probably damaged when I inserted it as the holes on the pcb are wider
> than the lead spacing on the capacitor). The final clue was when I
> broke an unrelated capacitor lead off which showed how easily they can
> be damaged (I've put hundreds of capacitors into circuits without
> issue before), The other clue was that when I touched my frequency
> meter probe to TP1 I got a very brief reading before it dropped to
> zero, and while it would continue to read zero if I touched tp1
> repeatedly, if I left it for a while (a minute or so) then touched the
> probe again, I once again got a brief reading. This suggested to me
> that T5 was probably OK (your telling me it was a Hartley oscillator
> helped there as I then looked it up to get a better idea of the
> operation).
>
> Lets hope it doesn't take me two weeks to get each of the various
> tests to pass!
>
> Thanks again,
>
> Matthew
>
> On 15/07/2012 14:14, Don Wilhelm wrote:
>> Matthew.
>>
>> Zero Hz. says that Q18 is not oscillating.
>> To help you visualize a little better, forget about the PLL part and
>> concentrate on Q18 only. That is just a Hartley oscillator.
>>
>> You have already shorted out the VFO ALC with the short across C60 -
>> and that is a good debugging step. The tuned circuit inductance
>> consists of L30 in parallel with the red winding of T5 and the
>> capacitance is made up of the varactors and capacitors switched in
>> and out of the circuit by K13, K14 and K15. That is really all there
>> is to it as far as basic oscillation is concerned.
>> Once it oscillates, then you can consider the other "appendages" like
>> the R30 voltage and the VFO ALC.
>>
>> So, go over the circuit once again with that in mind. There is a
>> reason Q18 is not oscillating - Several possibilities: the green
>> winding of T5 is wound backwards, the diodes are oriented backwards,
>> The varactors are mounted backwards, Q18 is oriented incorrectly,
>> Q18 is damaged,
>>
>> Note also that the path to TP1 includes U3 (which also could be
>> failing). Since you have an external frequency counter, check for
>> oscillation at the source or Q18 rather than just at TP1.
>>
>> You should first be trying to just get Q18 to oscillate. Once that
>> is working, the other parts come into play to make the frequency of
>> oscillation correct.
>>
>> 73,
>> Don W3FPR
>>
>>
>>
>> On 7/15/2012 3:44 AM, Matthew Ellis wrote:
>>> Hi,
>>>
>>> I'm struggling to track down an issue with the VCO test in part 2 of
>>> the
>>> alignment for my K2 (page 64 in my manual).
>>>
>>> The 4MHz Oscillator calibration looks OK as the frequency on TP3 shows
>>> as 12096hz stable (both on the internal test probe and an external freq
>>> counter). The PLL test is in range as well. But I get nothing
>>> (0hz) on
>>> TP1 for the VCO test with both the internal probe and a standalone
>>> frequency meter.
>>>
>>> I've checked and re-wound/re-fitted Transformer 5, gone over my
>>> assembly
>>> with a magnifying glass a few times (both top and bottom side of the
>>> pcb), confirmed all the components in the VCO area are present and
>>> correctly oriented. I've also used a signal scanner on the i2c
>>> lines to
>>> confirm the pll ic is getting the 'change freq' instructions. Most
>>> voltages appear good compared to the manual, although the voltage on
>>> Q16
>>> C and Q17 G is off (initially 8v then dropped to near 0v after i
>>> re-soldered the joints of resistor R9). I have shorted C60 to
>>> completely bypass the VFO ALC (suggestion from Elecraft).
>>>
>>> All prior tests were fine, everything in expected range. Also the
>>> correct frequency shows on pins 1 and 2 of U4 (MC145170), and voltages
>>> look good on U3,4 & 6.
>>>
>>> I'm in the UK, so sending it back to Elecraft is not my preferred
>>> option
>>> (time/cost).
>>>
>>> Has anyone got experience of issues in this area?
>>>
>>> Thanks,
>>>
>>>
>>
>
>