[Elecraft] [K2] VCO Not Oscillating

[Matt VK2RQ]

Hi Joseph,

Just taking a closer look at the voltages you reported on Q16, Q17 & Q18:
Q17 should be a 2N7000 MOSFET, but the measurements you provided talk about Base, Emitter and Collector (rather than Gate, Source and Drain).

Also, the Drain of Q17 has a DC connection to the Source of Q18. You report the Source of Q18 as being 6.64V, but if there is no oscillation then this isn't consistent with the voltages you reported on Q17.

Can you maybe check you have used the right transistors, verify the orientation/pin outs, and recheck that the voltages you are reporting against each transistor and each transistor terminal are correct? Somehow something doesn't quite seem to add up with what you reported below :-)

Another obvious thing is to verify is the orientation of ICs U3 and U4.

73,
Matt VK2RQ

> On 29 Apr 2014, at 10:22 am, Joseph Baxley via Elecraft <elecraft at mailman.qth.net> wrote:
> 
> Hi,
> 
> I've been trying for the last four days to figure out what is wrong with my
> rig.  I'm at Phase 2 Test and Alignment and got to testing the frequency of
> the VCO.  It had a reading of 00000.  Also the voltage on R30 was 7.87V. 
> This is consistent with the VCO not oscillating.  The reference oscillator
> works fine and was within the expected ranges when I looked at it.  What I
> was able to notice was that U4 on the RF board has two pins with voltage
> values that are out of spec.  Pin 1 has 0.9V and pin 13 has 0V.  If I read
> the table they should be 2.1 and 4V respectively.  It also seems that the 0V
> on pin 13 is causing a 0V reading on pin 6 of U6.  Otherwise U6 is in spec. 
> I got out my oscilloscope and got a Vrms of 1.13V on U4 pin 1.  There wasn't
> anything on pins 3 or 6 of U3.  The voltages for Q17, Q16, and Q18 are as
> follows:
> 
> Q17   E: 0V
>         B: 7.13V
>         C: 0.08V
> 
> Q16   E: 0V
>         B: 0V
>         C: 7.13V
> 
> Q18   G: 0.08V
>         S: 6.64V
>         D: 0V
> 
> I have been measuring and testing voltages and components for the last four
> days and have run out of things to look at for the moment.  If any of you
> can help me with what my problem is, I would be most grateful.
> 
> Sincerely,
> Joseph 
> KI4ITG
> 
> 
> 
> --
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