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PLL Reference Oscillator Range and VCO Test

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Dickie M0AUW

PLL Reference Oscillator Range and VCO Test

Hi,
I’m currently assembling my K2 but am stuck on the PLL reference Oscillator test.

In the frequency counter mode with the probe attached to TP3, I get a reading of 12099.03 kHz, when pressing band + I get 1298.99, Pressing band – I only get 00.467 to 00.475 changing rapidly. (Perhaps the probe is playing up but seems to work with other tests?)

However, with an external frequency counter attached I get 12099.00 and no change when pressing band +, but when pressing the – I get 11500 varying to 11700 at high speed.
I’ve checked solder joints around that area in particular at R19, RP2, L31, D16 and D17 and at U6 pin 5 am getting 3.90 volts.

Also on the VCO test I am getting a reading of 7738.64 but I suspect this will be out due to the PPL test?

Any help would be much appreciated – 73s Dick M0AUW

Don Wilhelm-4

Re: PLL Reference Oscillator Range and VCO Test

Dick,

If your internal probe works in TP2, then it is probably OK.

Good on the 3.9 volts at U6 pin 5, that part is encouraging, but it does
not entirely rule out a problem with the Thermistor board.
Skip that for now and first check to see if the problem is in the
digital side or the analog side of the DAC. Try the following tests in
order.

Monitor the voltage at U5 pin 7 while in CAL FCTR. When you tap BAND+
it should go to 4 volts, and when you tap BAND-, it should go to zero
volts. If it does not do that, you probably have a problem on the
digital inputs to U5. Those come from the control board - check the
soldering at U5 pins 1, 2, and 3, and CB U6 pins 19 and 24 as well as U8
pin 10.

If RF U5 pin 7 tests good, move on to monitor U6 pin 1. It should
change from zero volts with BAND- to near 8 volts with BAND+. If it
does not check all the soldering on the back of the Thermistor board,
especially checking for solder bridges.

If U6 pin 1 tests good, take a big step and monitor the voltage at the
anodes of D17 and D17. You should see the same voltage change as you
did at U6 pin 1. If not, check soldering and values for R19 and RP2.

If no problem was found in the tests above, then you have a problem with
the PLL oscillator itself (Q19 circuit). Check resistance to ground
from the source of Q19. If you do not see near 270 ohms, check the
soldering of R20 and the lead stripping and tinning of RFC14.

No problem solved so far? Check capacitors C84 and C85 to be absolutely
certain they are 120 pF (marked 121). The makings on those small blue
bodied capacitors is very difficult to read and you may have to remove
them and check under high magnification and a strong light.

If all the above is good, it should work.

73,
Don W3FPR

On 4/8/2013 6:37 AM, Dickie M0AUW wrote:

> Hi,
> I’m currently assembling my K2 but am stuck on the PLL reference Oscillator
> test.
>
> In the frequency counter mode with the probe attached to TP3, I get a
> reading of 12099.03 kHz, when pressing band + I get 1298.99, Pressing band –
> I only get 00.467 to 00.475 changing rapidly. (Perhaps the probe is playing
> up but seems to work with other tests?)
>
> However, with an external frequency counter attached I get 12099.00 and no
> change when pressing band +, but when pressing the – I get 11500 varying to
> 11700 at high speed.
> I’ve checked solder joints around that area in particular at R19, RP2, L31,
> D16 and D17 and at U6 pin 5 am getting 3.90 volts.
>
> Also on the VCO test I am getting a reading of 7738.64 but I suspect this
> will be out due to the PPL test?
>
> Any help would be much appreciated – 73s Dick M0AUW
>
>

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Dickie M0AUW

Re: PLL Reference Oscillator Range and VCO Test

Hi Don,
Many thanks for your quick reply.

U5 pin 7 good 4.8v at + 0 at -
U6 pin 1 good 7.68v at + 0 at -
D16 and 17 checked, same voltage change as U6 pin1
Q19 I'm getting a reading of 257 ohms
C84 and 85 are checked and correct

While I had the time I removed the thermistor board , all looked OK.
I will double check RFC14 and if necessary rewind and re-tin; I will also go over all the soldering again, 9 times out of 10 its a bridge or a soldering issue but I have to say I can't locate anything yet.
Will let you know how I get on

73s - Dick M0AUW

Don Wilhelm-4

Re: PLL Reference Oscillator Range and VCO Test

Dick,

All that sounds good, and may not be the source of your problem.

You mentioned that you had a frequency counter.
Do the CAL FCTR test with BAND+/- using your external frequency counter
and see if you obtain the expected frequencies.
If so, take a very good look at your internal counter probe, especially
the insertion of the crimp pins into the housing. If those crimp pins
are not inserted correctly (with the crimp pin locking tabs locked in
the rectangular holes of the housing), the signal from the test point
may not be adequate getting to the control board. Also the braid on the
coax must be on the pin closest to the left side panel when the probe is
attached to the Control Board.

I have not seen it lately (in the past 2 or 3 years) but a while back we
had trouble with the frequency response of Q9 and Q10 on the Control
board. If your external counter test is good and the probe is in good
shape, you could try replacing Q9 and Q10 with 2N2222 transistors - they
will work fine up through all the frequencies that internal counter needs.

73,
Don W3FPR

On 4/8/2013 2:23 PM, Dickie M0AUW wrote:

> Hi Don,
> Many thanks for your quick reply.
>
> U5 pin 7 good 4.8v at + 0 at -
> U6 pin 1 good 7.68v at + 0 at -
> D16 and 17 checked, same voltage change as U6 pin1
> Q19 I'm getting a reading of 257 ohms
> C84 and 85 are checked and correct
>
> While I had the time I removed the thermistor board , all looked OK.
> I will double check RFC14 and if necessary rewind and re-tin; I will also go
> over all the soldering again, 9 times out of 10 its a bridge or a soldering
> issue but I have to say I can't locate anything yet.
> Will let you know how I get on
>
> 73s - Dick M0AUW
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/PLL-Reference-Oscillator-Range-and-VCO-Test-tp7572321p7572344.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Dickie M0AUW

Re: PLL Reference Oscillator Range and VCO Test

Hi Don

I've removed RFC14 and re-tinned.
With an external frequency counter I'm getting a reading of 12099 at + and between 1100.00 and 11.600 at -, but its turning over rapidly. If I finger touch various components example relays 13 14 and 15 the signal will jump up dramatically towards 15/16000, but I suppose that's to be expected.

I checked the internal counter probe all seems correct re connections and I've re-soldered TP3, but any slight movement on the probe and the signal does vary but still around the 00.467 to 00.500 mark.

The only other abnormality is that on switch on I get a "Lo Batt" for a couple of seconds, puzzling as I'm using a 12v 5amp PSU, would this cause any issues?
By chance I do have some spare 2N2222 transistors so if all else fails I can replace Q9 and 10.

73s - Dick M0AUW

Don Wilhelm-4

Re: PLL Reference Oscillator Range and VCO Test

Dick,

Since your external counter fails to give the right frequency range with
BAND-, there is something more than the probe that is not right.
Look at the soldering of L31 and and the PLL crystal - reflow that
soldering as a first measure.
Check the value of RP2 - it should be 10k (last 3 digits 103).
Make certain D16 and D17 are not swapped. D16 should be an MV209 and
when viewed from the top looks about the same as a transistor. D17 is a
1SV149 which has a much thinner body. Check the orientation of D17
carefully too. It has 2 flat sides and the shorter flat side has
chamfered corners (or edges if you prefer). That shorter side is the
rounded side.

Because you have very close to the correct frequency with BAND+, I think
is happening.is the varactors are just fine when the reverse voltage is
high, but when the voltage is low, the capacity presented by the
varactors is too low. That could be caused by D16 and D17 swapped or
D17 in backwards, or not good connections to L31 and the crystal.

Since you may have a potential problem with the probe, check with your
external counter for both the PLL high and low frequencies. There is
nothing magic about the internal probe for that part of the procedure,
it is simply a check that the circuit is oscillating and the crystal and
varactors and L31 are behaving as expected. You have to get that
situation solved before the other tests will be meaningful. After you
have the correct frequencies on your external counter, if the internal
probe does not produce nearly the same frequencies, then you can
investigate the probe.

As for the LoBAtt message, that is likely coming from the plugging of
the 3 pin header P7 on the Control Board. The jumper should be in the
INT position (the 2 pins closest to the center of the board). If it is
plugged correctly, review the soldering on CB P7, R9, R19, and U3.

73,
Don W3FPR

On 4/9/2013 3:46 PM, Dickie M0AUW wrote:

> Hi Don
>
> I've removed RFC14 and re-tinned.
> With an external frequency counter I'm getting a reading of 12099 at + and
> between 1100.00 and 11.600 at -, but its turning over rapidly. If I finger
> touch various components example relays 13 14 and 15 the signal will jump up
> dramatically towards 15/16000, but I suppose that's to be expected.
>
> I checked the internal counter probe all seems correct re connections and
> I've re-soldered TP3, but any slight movement on the probe and the signal
> does vary but still around the 00.467 to 00.500 mark.
>
> The only other abnormality is that on switch on I get a "Lo Batt" for a
> couple of seconds, puzzling as I'm using a 12v 5amp PSU, would this cause
> any issues?
> By chance I do have some spare 2N2222 transistors so if all else fails I can
> replace Q9 and 10.
>
> 73s - Dick M0AUW
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/PLL-Reference-Oscillator-Range-and-VCO-Test-tp7572321p7572398.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Dickie M0AUW

Re: PLL Reference Oscillator Range and VCO Test

Hi Don,

I checked out RP2 and was only getting 9.2K on two pins only, (the two furthest from the dot) When measuring from the dot to the 8th pin nothing was showing on the DMM. So I have removed it but unfortunately it has broken, So I will have to replace.
Does it have to be an 82k or could I get away with 100k? For some reason I'm having problems finding a Sip (network) resistor at 82k in this country!
Also D16 looks suspect so I will replace.

73s - Dick

Dickie M0AUW

Re: PLL Reference Oscillator Range and VCO Test

Apologies, Just realised Its a 10k network resistor!