K2 Alignment & Test, Part II PLL problem, Continued

[rootboy-3]

It looks like the original was lost when my Bellsouth email session timed out. Hopefully it won't be posted twice (my apologies in advance).


> Be certain you have correctly installed L31 and that it is the 10 uH
> shielded inductor.  Resistor R115 is about the same size - is there a
> possibility that you exchanged these parts?

> Be certain you have D16, D17 and D18 inserted the proper way around (the
> Parts Placement Diagram is handy for checking diode orientation).  Check the
> soldering on these diodes.

> Be certain R19 and RP2 is well soldered.  While you are checking soldering,
> also check R20 and R21, RFC14 C84 and C85, and Q19.  You can check the
> toroid lead soldering for RFC14 by measuring the resistance to ground from
> the source of Q19 - expect a small bit more than 270 ohms.

> 73,
> Don W3FPR


Thanks for the help Don. :)

I tried your suggestions (and a few others as well) and L31 (which is a 12 µHz inductor on my unit) is the correct part.

Diodes D16, D17, & D18, are in properly and pass their in-circuit tests just fine.

R19, RP2, R20, R21, RFC14, C84, C85, Q19, RFC14, Q19 and the thermistor board are all installed properly and certainly look good.


Scott at Elecraft suggested holding the 4, 5, & 6 buttons while turning the unit on (which showed "INFO 201") to see if that corrected the problem but no luck there either.

I took reading off of U6 while switching between "BAND -" and "BAND +" in "CAL FCTR" mode, and here's what I got:

BAND +, The display reads 488Hz  (Bad)

U6 Readings:
Pin 1 = 7.63V
Pin 2 = 4.09V
Pin 3 = 4.09V
Pin 4 = 0V
Pin 5 = 3.96V
Pin 6 = 4.91V
Pin 7 = .02V
Pin 8 = 7.95V


BAND -, The display reads 12086Hz  (Good)

U6 Readings:
Pin 1 = .00V
Pin 2 = .09V
Pin 3 = .02
Pin 4 = 0V
Pin 5 = 3.96V
Pin 6 = 3.96V
Pin 7 = 1.64V
Pin 8 = 7.95V


Pins 2, 3, 6, especially Pin 6, are out of tolerance.

Taking resistance readings off of the thermistor board looks good.

Pins 6/7 to Pin 8 reads about 5k ohms.
Pins 4/5 to Pin 8 reads about 295 ohms.
Pins 2/3 to Pins 4/5 reads about 1.96k ohms.
Pins 6/7 to Pin 1 reads about 8.76k ohms.
Pin 1 to Pins 2/3 reads about 1.8k ohms.

All of these readings more or less mathematically work out to what the meter says (with the exception of the second reading which is 8V to Ground so no surprise there).

The output from the DAC is 4.092 (4,092 counts), so it's near its top end.


My partner suggests removing R19 and inserting a pot to swing the voltage going into the oscillator circuit from 0 to 7-ish volts to see if that stabilizes.


I got another suggestion to double check D36 for proper installation. It's in correctly, and checks out (in circuit) okay.

Possibly I left a component out, so I'll double check that I didn't skip anything during the installation phase.


Thanks again for all the help,

John

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[Don Wilhelm-3]

John,

For the time being (until you solve the current problem) the only voltages
at U6 that matter are pins 1, 2 and 3 - and those are correct.  The other
pins will likely fall into line after you have this problem fixed and if not
there is another problem with the VCO.

Right now, the voltages being fed out of U6 pin 1 are correct for the
stimulus you provided (CAL FCTR and tapping BAND+ and BAND-).  Now check to
see if that (proper) 0 to 8 volt swing between pressing BAND+ and BAND- is
carried on through R19 and then through the RP2 sections and then onto the
cathodes of D16 and D17.  If you get a decent voltage swing between BAND+
and BAND- (you can expect a bit of voltage drop on the 8 volts end) at the
varactor cathodes, then look for something else wrong in the PLL Reference
oscillator (upper left of the schematic sheet - but only as far to the right
as TP3), the PLL chip does not matter until the PLL Reference oscillator is
functioning properly.

If you do get a good voltage swing at the varactors, then all I can say is
either Q19 oscillations quit when the varactor capacitance is reduced, or
there is something wrong at C84, C85, D17 or D16 which is stopping the
oscillation.  If you suspect Q19 itself, you could try swapping it with one
of the J310s on the Control Board at Q6 or Q7 (these in a less-critical
audio circuit rather than being used as an RF Oscillator).

73,
Don W3FPR

> -----Original Message-----
>
> Thanks for the help Don. :)
>
> I tried your suggestions (and a few others as well) and L31
> (which is a 12 µHz inductor on my unit) is the correct part.
>
> Diodes D16, D17, & D18, are in properly and pass their in-circuit
> tests just fine.
>
> R19, RP2, R20, R21, RFC14, C84, C85, Q19, RFC14, Q19 and the
> thermistor board are all installed properly and certainly look good.
>
>
> Scott at Elecraft suggested holding the 4, 5, & 6 buttons while
> turning the unit on (which showed "INFO 201") to see if that
> corrected the problem but no luck there either.
>
> I took reading off of U6 while switching between "BAND -" and
> "BAND +" in "CAL FCTR" mode, and here's what I got:
>
> BAND +, The display reads 488Hz  (Bad)
>
> U6 Readings:
> Pin 1 = 7.63V
> Pin 2 = 4.09V
> Pin 3 = 4.09V
> Pin 4 = 0V
> Pin 5 = 3.96V
> Pin 6 = 4.91V
> Pin 7 = .02V
> Pin 8 = 7.95V
>
>
> BAND -, The display reads 12086Hz  (Good)
>
> U6 Readings:
> Pin 1 = .00V
> Pin 2 = .09V
> Pin 3 = .02
> Pin 4 = 0V
> Pin 5 = 3.96V
> Pin 6 = 3.96V
> Pin 7 = 1.64V
> Pin 8 = 7.95V
>
>
> Pins 2, 3, 6, especially Pin 6, are out of tolerance.
>
> Taking resistance readings off of the thermistor board looks good.
>
> Pins 6/7 to Pin 8 reads about 5k ohms.
> Pins 4/5 to Pin 8 reads about 295 ohms.
> Pins 2/3 to Pins 4/5 reads about 1.96k ohms.
> Pins 6/7 to Pin 1 reads about 8.76k ohms.
> Pin 1 to Pins 2/3 reads about 1.8k ohms.
>
> All of these readings more or less mathematically work out to
> what the meter says (with the exception of the second reading
> which is 8V to Ground so no surprise there).
>
> The output from the DAC is 4.092 (4,092 counts), so it's near its
> top end.
>
>
> My partner suggests removing R19 and inserting a pot to swing the
> voltage going into the oscillator circuit from 0 to 7-ish volts
> to see if that stabilizes.
>
>
> I got another suggestion to double check D36 for proper
> installation. It's in correctly, and checks out (in circuit) okay.
>
> Possibly I left a component out, so I'll double check that I
> didn't skip anything during the installation phase.
>
>
> Thanks again for all the help,
>
> John
>
>

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