[Elecraft] [K2] VCO Not Oscillating

Wed Apr 30 00:57:07 EDT 2014

Joseph,

Blame it on poor lighting at the computer (and my eyes) - yes, C60 is 
the appropriate capacitor.
So the VFO ALC is not the problem - you will have to discover why the 
VFO is not oscillating.  It could be a problem with Q18 or anything in 
its circuit.  Do check Q18 for the correct FET type (J310) and the 
orientation of D13 and D8 - refer to the parts placement diagram in the 
back of the manual for the diode orientation.

73,
Don W3FPR

On 4/29/2014 10:51 PM, Joseph Baxley via Elecraft wrote:
> Don,
>
> Thanks again.  I had one question from your last email.  Did you mean C60?   I couldn't find C50 in the VFO circuit.  I shorted C60 which put the drain to ground.  Still no help.  The BFO is working though, so that's good news.  I also checked D13 and D8.  They match the outline on the board, so they should be good.  I will try again tomorrow when I've had some rest.  Sometimes I've found fresh eyes help me see things I missed the night before.
>
> Joseph
>
>
>
>
> On Tuesday, April 29, 2014 9:15 PM, Don Wilhelm-4 [via Elecraft] <ml-node+s365791n7588159h64 at n2.nabble.com> wrote:
>   
> Joseph,
>
> See if the VFO is oscillating.  Check the internal counter probe by
> plugging it into TP2 and use menu CAL FCTR - you should see a frequency
> near 4913 kHz (the BFO frequency).  If that is good, the counter probe
> should be working.  Then plug the probe into TP1.  The frequency should
> be near the K2 dial frequency plus 4913 kHz.  If you see that frequency,
> all is OK with the VFO.
>
> If you instead see all zeros, the VFO is not oscillating, and you will
> have to figure out why.
> You have already checked the winding of T5, so there may be something
> else.  Check the orientation of D13 and D8 as starters. Then eliminate
> the VFO ALC from the picture by placing a short from the drsin og Q17 to
> ground (a convenient place to do that is to put a temporary solder
> bridge across the leads of C50).  Do you get a VFO frequency reading
> with that in place?  If so check the soldering of the VFO ALC
> components.  Look on the schematic and find on sheet 1 for the RF Board
> all the components in the area labeled VFO ALC and check the soldering
> of all those components - remove the solder bridge from C50 and see if
> it still oscillates.  If it does, you should be on your way to success.
>
> 73,
> Don W3FPR
>
> On 4/29/2014 9:13 PM, Joseph Baxley via Elecraft wrote:
>
>> Don,  Matt,
>>
>> I looked at the transformer and have double checked him.  I saw that there
>> was electrical continuity between leads 1 & 2 and 3 & 4 (i.e. zero Ohm
>> resistance between said leads).  Also, 3 & 4 are the green leads.  I checked
>> that the green wires weren't crossing and that they were spaced each turn
>> between the red wires.  I did notice that they weren't exactly centered,
>> with more red turns before lead three than after lead four.  I pulled the
>> transformer out and rewound the green wires to center them and see if it
>> helped any.  No dice.  Also I checked the number of turns, 16 red and 4
>> green.  I'm intimately familiar with not having properly stripped the wires.
>> That was a problem building my K1!
>>
>> I'm fairly certain then that the transformer is not the problem.  I've been
>> checking things like the diodes that run through the VCO to make sure that I
>> have not put in one backwards.  I've also been looking for cold joints or
>> solder bridges.  Haven't found one yet.
>>
>> Thanks,
>> Joseph
>>
>>
>>
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