Posted by
Don Wilhelm on
Jan 18, 2019; 3:33pm
URL: http://elecraft.85.s1.nabble.com/K2-VCO-Alignment-T5-L30-tp7648249p7648250.html
Tom,
Normally I would say to spread or compress the turns on T5, but Elecraft
encountered a batch of J310 FETs that do not work very well at Q19 - the
PLL reference oscillator. These troublesome FETs have now been purged
from the Elecraft stock, that the problem should go away going forward.
I am not sure that is your problem, but it is worthy of checking.
First question is - did you get good frequency readings for the PLL
Reference Oscillator range? If it fails, you see a strange frequency
reading at the high frequency end (when BAND+ is tapped).
Now, the other "funny" thing is that it sometimes checks OK with the
internal counter probe plugged into TP3, but fails when the probe is
removed.
Under those conditions, the PLL and VFO do not lock together
So the first thing to try is to solder a 10 to 15pF capacitor between
the source of Q19 and ground. Then between a combination of adjusting
the red turns on T5 and L30 see if you can obtain the correct R30 voltage.
If that is successful, then all should be well.
If not successful, get a replacement Q19 from Elecraft. Send the part
number and description to
[hidden email] and ask for a replacement.
If that does not correct things, then email me and we can go through
some other checks to determine the source of the failure.
73,
Don W3FPR
On 1/18/2019 8:48 AM, K2bew wrote:
> Don et al,
>
> Since I know Don monitors the reflector as well as the support emails,
> rather than email Don directly I thought I would ask the question on here
> because I know I always find it helpful to read other peoples questions on
> here and Don's answer.
>
> Building the K2 I am at the VCO Alignment voltage check on R30 and
> adjusting L30.
> VFO frequency set at 4000.00 kHz
> I initially got 3.5 volts and bottomed out L30 to get it to 5.5 volts, and
> then I over screwed it to try to get that last half a volt and ended
> damaging it, so, then I carefully took out L30 and put in a new one.
>
> I also took out T5 and rechecked all the ends for continuity, rewound the
> green wire to space it exactly in the middle of the red winding and spaced
> everything evenly. I confirmed it is the large yellow core, I have 16 on
> the red wire and 4 on the green (by the way the illustration shows 14 turns
> of red) . I verified I have R30 as Br-R-Br 120 ohms with both my DVM and by
> color, and I verified C72 is 271, and I reflowed the solder on both.
> With a new 4.7 inductor (large slot, no red mark) in L30 I now get 2.75
> volts on the left side of R30 to start with and it bottoms out at 4.5 volts
> (I was very careful to not bottom it out too hard this time and damage this
> one, and I have already ordered a couple new ones from Elecraft).
>
> What else can I do to increase that voltage? Would changing the number of
> windings on T5 change it enough to get to 6 volts?
>
> Thank you and 73,
> Tom Bewick K2BEW
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