Elecraft

Re: RE: K2 Alignment & Test, Part II PLL problem, Continued

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rootboy-3

Re: RE: K2 Alignment & Test, Part II PLL problem, Continued

I'm back....

I got the new components (D16, D17, C84, C85, & Q19) from Scott over at Elecraft and installed them. I still got the same readings so I re-read the instructions and checked each and every component to make sure that I had everything installed correctly.

I did find one mistake, I had soldered C88 to pins 11 & 12 of U4 instead of pins 12 & 13. I relocated the cap and the frequency went up slightly (reading 524 instead of 495). The cap measured ~58 picos (in circuit) so it's in the ballpark.

I also touched up a few soldering joints along the way, more for looks than anything else.

The voltage readings on pins 1, 2, & 3 of U6 are the same as before, and both variactors seem to be working just fine.

Any ideas?

Thanks again for all of your help,

John

>
> From: "Don Wilhelm" <[hidden email]>
> Date: 2006/04/11 Tue PM 08:18:46 CDT
> To: <[hidden email]>,
> <[hidden email]>
> Subject: RE: [Elecraft] K2 Alignment & Test, Part II PLL problem, Continued
>
> 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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rootboy-3

Re: RE: K2 Alignment & Test, Part II PLL problem, Continued

Both you and Don made that same suggestion, so I called up Scott today and asked him for another of these as well (the man has the patience of a saint).

For grins I took C87 out so that I could isolate the oscillator section from the PLL section (U4). I ended up seeing 0Hz for the high range (was 450 -550) but still got my trustworthy 12086 for the low end reading. The reason why I yanked C87 was because I was concerned that my mistake with C88 might have damaged U4. This doesn't seem to be the case.

So it looks like U4 isn't causing any trouble, and the other good news is that the list of original parts left to be replaced is dwindling. :)

Thanks again for all the help,

John

>
> From: "k4zm" <[hidden email]>
> Date: 2006/04/19 Wed AM 07:26:45 CDT
> To: <[hidden email]>
> Subject: Re: RE: [Elecraft] K2 Alignment & Test, Part II PLL problem, Continued
>
> John:
>
> The other possibility is a bad X1. Maybe it can't oscillate at that wide a
> frequency range. As stated earlier it has to be in the area of the PLL Ref
> Oscillator because that is all you are looking at in that test. The test is
> to make sure the crystal can be shifted the proper amount so that the PLL
> circuits will work properly.
>
> 73
> Jim Younce K4ZM
>
>
>