http://elecraft.85.s1.nabble.com/K2-VCO-Alignment-T5-L30-tp7648249p7648312.html
I've got good news. I had the wrong Capacitor in the BFO section and just happened to have a replacement for C169. Whoops I told on myself! Any way at TP2 +4917.74 and -4911.90 for a difference of 5.84. Don struck again. Hi Hi.. I'll check the voltages on RP6 tomorrow.
Ed.. AB4IQ
I tried a 15pf cap ( what I had on hand) at the source of Q19 to ground and I got .025v on R30 that did not change with the adjustment of L30, essentially no voltage.
So, I took it off and it went back to 4.5 volts. So, then I tried Vicenç, EA3ADV's suggestion and I put 17 turns on the red wire of T5.
That got me a voltage of 8.5V on R30 with L30 bottomed out that I was able to easily back off to a stable 6 volts.
I went ahead and did the voltage tests on the other bands and had a nice range of 1.844 to 6 volts as my low and high on the VCO.
However, new problem. I went on to the test the BFO and I have 0000.04 kHz.
I went to the trouble shooting guide and I have 0.058 Vrms on pin 6 of U11 with the RF probe.
Looking at the archives of the reflector that would indicate that U11 is bad and I need a replacement, correct? or are there other things I should look at first?
The good thing is I'm becoming very accustomed to the radio and enjoying the trouble shooting.
> 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
>