日期︰ 2014年05月12日 (週一) 11:59 AM
主題︰ Re: [Elecraft] [K2] VCO Not Oscillating
Hey,
I wanted to let you guys know that the root cause has been found. I asked
Don to look at the radio and the root cause was that I had misplaced a 1pF
cap at C68 which was labeled 1D. C68 was supposed to be 10pF. It
Hey,
I wanted to let you guys know that the root cause has been found. I asked
Don to look at the radio and the root cause was that I had misplaced a 1pF
cap at C68 which was labeled 1D. C68 was supposed to be 10pF. It was a
stupid construction mistake after all. Perhaps this can serve as a ni
P.S. I really would like to thank you all for your help.
--
View this message in context:
http://elecraft.365791.n2.nabble.com/K2-VCO-Not-Oscillating-tp7588086p7588438.html
Sent from the Elecraft mailing list archive at Nabble.com.
__
Don, Matt,
It is possible that I've mislabeled things, though I was trying to follow
the diagram they have before the schematics that describes each part.
Really I've not got a lot of experience with electronics beyond a couple of
classes in college. It's not something they stressed in the physi
Joseph,
I don't know if you are mislabeling the leads of Q18 or not, but those
voltages and the leads do not make sense.
The Drain of Q18 is connected to the 8B voltage rail through a 33 ohm
resistor and should have almost 8 volts on it.
The Gate is biased by the rectification of the RF voltage
Ok, that makes more sense now, although we now have the Drain of Q17
at 0.08V connected to the Source of Q18 at 6.64V via the primary
(green) winding of T5. I would hazzard a guess that there is also a
clerical error with the Q18 voltages, and that the Source is at 0.08V,
same as the Drain of Q17,
Matt,
My reason for asserting that the VCO is not oscillating is two-fold. One,
there is no frequency at TP1 when I touch it with the probe, but there is
when I touch TP2 and TP3. Both of these test points show a correct
oscillation of 4.9MHz and 12.09MHz respectively. Second, when I applied my
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
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 t
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 boa
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
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
Joseph,
Yes, leads 1 and 3 should be coming out of the top of the core, but the
leads must look like the illustration on page 56 of the manual, the
green wires must not cross over each other, but be wound between the red
wires.
You can check with the internal counter probe or the RF Probe to
Yes, leads 1 & 3 should come out the top of the core. However, you also need to
make sure the windings are in the same direction, like in figure 6-16,
otherwise you are applying negative instead of positive feedback, and the VCO
won't oscillate.
Also, make sure leads 1 & 2 are both red, and go
Don,
Thanks for the reply. I should have mentioned that I checked the windings on
T5. Pins 1 and 3 should be coming out of the top of the core, no? That's what
I have. I also used the yellow core for the transformer.
Thanks,
Joseph
On Monday, April 28, 2014 8:43 PM, Don Wilhelm-4 [via Ele
Joseph,
The first thing to check is T5. The direction of the windings is
critical, and the leads must be in the proper holes as shown in the
diagrams in the manual. In other words, the sense (direction) of the
green wire turns on T5 must be the same as the direction of the red wire
winding.
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 0. Also the voltage on R30 was 7.87V.
This is consistent with the VCO not oscillating. The reference osci
17 matches
Mail list logo
