Posted by
Don Wilhelm-4 on
Jul 17, 2012; 10:49pm
URL: http://elecraft.85.s1.nabble.com/K2-Alignment-and-Test-Part-II-VCO-Test-fails-tp7559122p7559337.html
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,
>>>
>>>
>>
>
>
______________________________________________________________
Elecraft mailing list
Home:
http://mailman.qth.net/mailman/listinfo/elecraftHelp:
http://mailman.qth.net/mmfaq.htmPost: mailto:
[hidden email]
This list hosted by:
http://www.qsl.netPlease help support this email list:
http://www.qsl.net/donate.html