subject:"\[Elecraft\] K2 VCO Alignment only 0.02V @ R30"

So this morning I started rechecking everything. I've found that the 5V on
U4 pin 5 is intermittent. Not in a way that would indicate a loose or poor
connection, but either that it is there, or it isn't (mostly isn't) when
powering up the unit. U7 always has the 5V on pin2. I checked the
resistance between U7 pin2 and U4 pin 5 and found about 300k. Looking at
the schematics however, it looks like U4 pin5 is actually connected to U7
pin5 (SDO). There is less than 1 ohm of resistance between U4 pin5 and U7
pin5, so it would appear that U7 may have an issue.

The other odd thing is that even when there is 5V coming into U4 pin5, the
symptoms at R30 (0.020V) and the low band frequencies are still there. It
looks like U7 may provide U4 a clock signal as well.

I was seeing the 8V at R30 after reflowing all of the joints near the PLL
Reference. Could the increase in temperature in the are have triggered the
thermistor?

The only thing changed between having the 8V at R30 last night and then
losing it was the rewinding of T5 to bring it back up to 16 turns of red.
The continuity checks are good through it, and L30 still changes the
frequency when adjusted.

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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

U7 pin 2 and U4 pin 5 are both the SDO signal which comes from the 
microprocessor over on the control board.
If you have 300k resistance between those two points there is a break 
between them.


I don't know why you mention U7 pin 5 (unless it was a typo) because 
that pin is connected to ground.


U7 feeds U6A which in turn controls the voltage on the PLL varactors. 
Your PLL is working just fine, so there is no problem there.
Recheck the resistance between U4 pin 5 and U7 pin 2, or better yet 
between U4 pin 5 and pin 24 of U6 over on the Control Board - you should 
have close to zero ohms.


73,
Don W3FPR

On 2/3/2013 10:51 AM, JeremyJones wrote:

So this morning I started rechecking everything.  I've found that the 5V on
U4 pin 5 is intermittent.  Not in a way that would indicate a loose or poor
connection, but either that it is there, or it isn't (mostly isn't) when
powering up the unit.  U7 always has the 5V on pin2.  I checked the
resistance between U7 pin2 and U4 pin 5 and found about 300k.  Looking at
the schematics however, it looks like U4 pin5 is actually connected to U7
pin5 (SDO).  There is less than 1 ohm of resistance between U4 pin5 and U7
pin5, so it would appear that U7 may have an issue.

The other odd thing is that even when there is 5V coming into U4 pin5, the
symptoms at R30 (0.020V) and the low band frequencies are still there.  It
looks like U7 may provide U4 a clock signal as well.

I was seeing the 8V at R30 after reflowing all of the joints near the PLL
Reference.  Could the increase in temperature in the are have triggered the
thermistor?

The only thing changed between having the 8V at R30 last night and then
losing it was the rewinding of T5 to bring it back up to 16 turns of red.
The continuity checks are good through it, and L30 still changes the
frequency when adjusted.




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Looking over the board I did find that I had U8 C45 connected to pin7 instead
of pin6.  That has been corrected.

U6 pin 24 to U4 pin5 is less than 1 ohm, however U6 pin24 to U7 pin2 is 300k
ohm.  I don't see any damage on the board.

I also noticed going back to the beginning for the resistance checks on the
control board that Q1 collector should be great than 1M, but is reading 5k.



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Jeremy,

Do I recall correctly that you had a good PLL range? If so, I have
trouble believing there would be 300k resistance from CB U6 pin 24 to RF
U7 pin 2 while you have zero ohms to U4 pin 5. Are you certain you
counted the pins correctly? Pin 1 has a circular solder pad and the
rest are rectangular.

If you want to check the operation of RF board U7, monitor the DC
voltage at pin 7 while rotating the VFO knob - the voltage should change
gradually while tuning through a 10 kHz range and then jump back to its
lowest (or highest depending on which way you rotate the knob) at the
end of each 10 kHz interval.

Did you remove the Control Board when you made the measurement on the
collector of Q1? If not, then somewhere in the vicinity of 5 k is not
unreasonable.

73,
Don W3FPR

On 2/3/2013 12:41 PM, JeremyJones wrote:

Looking over the board I did find that I had U8 C45 connected to pin7 instead
of pin6. That has been corrected.

U6 pin 24 to U4 pin5 is less than 1 ohm, however U6 pin24 to U7 pin2 is 300k
ohm. I don't see any damage on the board.

I also noticed going back to the beginning for the resistance checks on the
control board that Q1 collector should be great than 1M, but is reading 5k.

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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Rechecked the resistance, and indeed there is 300k from U6 pin 24 to U7 pin2. 
Looking at the schematic in the manual, it shows U6 pin24 connected to U7
pin5 and U8 pin11.  At this point I do have less than 1 ohm.

The schematic shows U6 pin23 connected to U7 pin2 which is reading less than
1 ohm.

The control board was removed when checking Q1, and it is showing 4.2k to
ground.



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

I am sorry, I had the wrong IC,  RF board U5 pin 2 should be connected 
to Control Board U6 pin 24.  Yes, it also connects to Control Board U7 
pin 5 and Control Board U8 pin 11, as well as RF board U4 pin 5.


73,
Don W3FPR

On 2/3/2013 3:45 PM, JeremyJones wrote:

Rechecked the resistance, and indeed there is 300k from U6 pin 24 to U7 pin2.
Looking at the schematic in the manual, it shows U6 pin24 connected to U7
pin5 and U8 pin11.  At this point I do have less than 1 ohm.

The schematic shows U6 pin23 connected to U7 pin2 which is reading less than
1 ohm.

The control board was removed when checking Q1, and it is showing 4.2k to
ground.



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

No problem Don, you've been a huge help. 

So I went back to the beginning and did all resistance checks in the manual
up to this point and everything is good. 

PLL range test @ 7100.00khz gives me 12099.13 high and 12086.33 low. 
VCO @ 4000.10 gives me 7840.33

I do still have some bad voltages on U4 and U6 which I'm tracing now to see
where everything goes to and comes from. 





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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

So I really thing that U4 is faulty. It's putting out 5.029V on pin13 when
that should only be 4V. All the components surrounding it seem to have the
correct voltages according to the manual.  I think I'll replace that and see
how things look after. 



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

5.029 volts at U4 pin 13 means that the PLL synthesizer IC is working.  
Remember that the manual voltages are for a properly working K2 that has 
the PLL IC in lock with the VFO frequency.  Your voltage only indicates 
an out of lock condition.


What is the R30 voltage now with that 5.029 volts at U4 pin 13?  You 
should now have some voltage there.  Can you adjust that voltage with 
L30?  If so, you should now be able to get everything within the normal 
range.


If you are still seeing zero volts at the left side of R30, then U6B or 
its components is at fault, not U4.


73,
Don W3FPR


On 2/3/2013 8:31 PM, JeremyJones wrote:

So I really thing that U4 is faulty. It's putting out 5.029V on pin13 when
that should only be 4V. All the components surrounding it seem to have the
correct voltages according to the manual.  I think I'll replace that and see
how things look after.



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[Elecraft] K2 VCO Alignment only 0.02V @ R30

I'm in the process of building a K2 and am having trouble at the Alignment
and Test part 2.  I've gone through at ton of previous posts here an have
been talking with Gary at Elecraft but no luck so far.  The main issues are
C22 only has adjustment less than 1khz (12085-12086) @ TP3, and R30 which
should have 6V only has 0.02V. 

Below is the email chain (bottom to top) with the trouble shooting Gary and
I went through.  Wonder if anyone has any ideas of what the issue might be,
or further trouble shooting steps to isolate the problem.

Thanks, 
Jeremy


From Jeremy
To Gary
Adjusting the windings on T5 and moving the slug in T30 up has given me
11914khz on 40m. The other bands are still way off. Cal PLL still gives
error 232. I've tried running it at 7000, 7050, and 7100khz. Checked the
diodes and all are correct and in the right spot. 

Oddly enough I was able to get it to run Cal PLL by turning T30 until I got
12003khz at TP1.  Came across this by forgetting the probe in TP3 and
running Cal PLL. Moved the probe to TP1 and adjusted T30 and Cal PLL ran. 

C22 only has an adjustment of less than 1khz (12085-12086) @ TP3. 
R30 which should have 6V only has 0.02V. 

Sent from my iPad

On 2013-02-01, at 5:11 PM, Gary Surrency g...@elecraft.com wrote:

The freq. is still too low at TP1. The PLL cannot lock and the VCO will not
be on freq. unless it can tune to approximately the freq.'s shown in the VFO
Table. Err 232 is what you will see when the TP1 freq. is not close enough
for the PLL/VCO to lock onto the expected freq.

Something still seems to be wrong too, with the VCO freq.'s on the upper
bands. Too low of freq. means there is either too much inductance or too 
much capacitance in the T5 circuit. If it is not T5 and some bands are OK or
close to OK, then it is likely that for some reason, there is too much C in
the circuit still. This could be from an incorrect cap, a VCO relay is not
releasing some of the caps, or the varactor diodes are of the wrong type or
are in the wrong places. Check to see if maybe you mixed up the MV209
diodes with the 1SV149 diodes.

Try expanding the red turns on T5 as much as possible, and turn the slug in
L30 so it is near the top of the coil. See if then the VCO freq. will come
close enough to the stated freq.'s for the PLL to lock when you do CAL PLL
which is done only on 40m. If it is not within about 5-10kHz, CAL PLL will
not succeed.
--
73, Gary AB7MY

=
supp...@elecraft.com
Elecraft Technical Support  
  
On 2/1/2013 4:52 PM, Jeremy Jones wrote:
Understand totally on the capability of the radios. We're going to be using
them as an easy way to practice and test improvised antennas. And if all
goes well ill be passing my civilian amateur exam next week. 

Did the hard reset. 
U6 pin1 checks out good. 
U6 pin 5 is 4v. 
RFC 15 shows 2.3ohms. 
No marks on any relays. 
Removed 1 turn from T5. VCO test now gives 8040khz, which is now in spec. 
Still only 20mV on R30. 
All capacitors correct according to the VCO table. 
Still get error 232 when trying Cal PLL. 

New VCO freqs
3500khz = 8067
7000khz = 11734
10100khz = 13820
14000khz = 16559
18068khz = 18407
21000khz = 14847
24890khz = 16558
28000khz = 18405

Those are up from what you said was already high. 
What next :)


Sent from my iPad

On 2013-02-01, at 3:38 PM, Gary Surrency g...@elecraft.com wrote:

Hi Jeremy,

OK on the civilian call sign. Note that our radios are primarily intended to
cover the US ham bands, and there is limited freq. coverage outside of those
ranges due to the design of the VCO/PLL. The K2 is not general coverage.

You might first try doing a hard reset by holding down the 4,5,6 buttons all
at the same time when the power is turned on. This ensures the IOC sets the
freq. boundaries correctly and all of the defaults are set. Release the
buttons in 2-3 seconds and then wait about 10 seconds for the INFO 201
initialization to complete normally. This is usually done the first time the
rig is turned on, but if it was interrupter or did not complete for some
reason, the rig could be in an indeterminate state.

The VCO frequencies you stated are too high. Try expanding the red turns on
VCO inductor T5, or if necessary - remove a turn.

Use care to not damage the plated through holes if you do need to remove T5
to rewind it.

 Be sure there is no mistake in ID-ing the caps in the VCO circuit too, and
make sure none of the VCO relays have any soldering iron burns to their
case, they are not reversed on the PCB, and the pins are well soldered. See
the VCO Table again for which caps are used on which bands, and verify those
are all correct, and they are well soldered, as well as the VCO relays that
switch them. Check each and every part and soldered connection in the VCO /
PLL area.

Check that U6 pin 1 (LMC662) on the RF Board moves between 0VDC and about
7.5VDC when you do the PLL range test. If not, there is probably a problem
with the little PLL reference oscillator thermistor board, usually a

Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

I have read your exchanges with Gary,

First, don't bother with the C22 setting - just set it to the midpoint 
(slot parallel with the long edge of the board) and leave it there until 
you have the rest of the K2 receiver working on all bands, and then go 
to my website www.w3fpr.com and do the procedures stated in the K2 Dial 
Calibration article there.


Taking things one step at a time - is the PLL Range correct at TP3? Tap 
BAND+ to bring it to the highest frequency (about 12100 kHz) then tap 
BAND- to get to the lower limit (about 12087 kHz)  Those frequencies can 
vary by 2 to 3 kHz from the target values and still be OK.


Once assured that the PLL Range is correct, then tackle the VFO frequencies.
You do have something wrong there because your frequencies are too low 
on all bands.  That indicates either too much capacity or too much 
inductance is present in the VFO circuit.  Look at the schematic for RF 
Board sheet 1.  The area in question is in the upper right corner - the 
input side of Q18 - as well as the VFO range Select components.


Is T5 wound on a yellow core?  If wound on a red core, it will have too 
much inductance.  Does L30 have a slot across the entire diameter of the 
tuning slug?  It should.
Look at the tops of D23, D24, D25 and D26.  They should have a top shape 
like Q18 and about the same size.  D21 and D22 should have a smaller 
body profile when viewed from the top.  The wider flat side of all those 
varactors should be facing toward the rear of the RF Board.


Your next step is to check the relays K13, 14 and 15.  The white stripe 
should be on the end toward the rear of the RF board.


Examine the bottom of the board for the soldering of those components in 
the VFO and VFO Range Select areas to be certain there are no tiny 
solder bridges.


If everything is correct, it *should* have close the frequencies listed 
in VCO Table on the Schematic Key page - within 3 to 5 kHz when 
everything is correct.


73,
Don W3FPR



On 2/2/2013 9:43 AM, JeremyJones wrote:

I'm in the process of building a K2 and am having trouble at the Alignment
and Test part 2.  I've gone through at ton of previous posts here an have
been talking with Gary at Elecraft but no luck so far.  The main issues are
C22 only has adjustment less than 1khz (12085-12086) @ TP3, and R30 which
should have 6V only has 0.02V.

Below is the email chain (bottom to top) with the trouble shooting Gary and
I went through.  Wonder if anyone has any ideas of what the issue might be,
or further trouble shooting steps to isolate the problem.

Thanks,
Jeremy




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Hi Don,

I set C22 to midway. 
PLL @ TP3 is 12099.12 - 12086.32. 
T5 is a yellow core, wound with 15 turns red and 4 green. I had to bring it
down to 15 turns as recommended by Gary to get 8253.86khz @ TP1 when tuned
to 4000.10 for the VCO test.  It was around 7694.39 with 16 turns. 
L30 is the correct part, and all diodes have been checked to ensure the
correct part and placement. 
Soldering has been checked. 
Verified C67, C65, C64, C68, D13, Q18 for value and orientation. 
Relays click when changing bands. 

Still getting the following readings. 
3500 = 8248.42
7000 = 12010.78
10100 = 14157.67
14000 = 16976.67
18068 = 18878.23
21000 = 15211.55
24890 = 16977.38
28000 = 18878.84

I am at a loss for what to look for next. Everything seems to check out, but
my readings are still off. Anyway I can try to isolate a faulty component?



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

Unless you have a typo, the 40 meter VFO frequency is too high while all 
the rest of the bands is too low.

Make certain that the value of C71 is 82 pF and re-flow its soldering.
Set the K2 to 7000 kHz and re-measure the VFO frequency - probe in TP1
Next (while you are still in CAL FCTR, turn the slug on L30 Without 
moving the VFO knob) to see if the frequency moves.  If it does not, 
re-flow the soldering on the pins of L30.  If the frequency does move, 
then T5 and L30 are properly connected, and that is what I wanted you to 
check.
Go to the secondary menu (tap DISPLAY) and check the parameter for D19 - 
it must be n.


When re-flowing the solder, use a hot (750 degF) iron and add just a 
tiny dab of solder - you actually only need to add a bit of flux.
Watch the solder to be certain it flows out fully onto both the solder 
pad and the lead.  If you can see a distinct edge to the solder on the 
pad, that connection is suspect - it did not receive enough heat or was 
not heated long enough.


If all was as expected for the tests above, inspect the pins of relays 
K13, 14 and 15 carefully - you are looking for any whisker of solder 
that would form a bridge between two pins.


Next, move your search to the left of the VFO on the schematic, and 
check all the components in the U6B circuit for correct values and good 
soldering.  Make certain all components are in the proper holes - 
sometimes there is a via hole next to a solder pad and the component 
lead can be placed in the via hole instead of the solder pad.  When you 
have finished that inspection, power on and check the voltage at U6 pin 
5.  If it is not 4 volts, you have a problem on the small thermistor board.


73,
Don W3FPR


On 2/2/2013 11:31 AM, Jeremy Jones wrote:

Hi Don,

I set C22 to midway.
PLL @ TP3 is 12099.12 - 12086.32.
T5 is a yellow core, wound with 15 turns red and 4 green. I had to bring it 
down to 15 turns as recommended by Gary to get 8253.86khz @ TP1 when tuned to 
4000.10 for the VCO test.  It was around 7694.39 with 16 turns.
L30 is the correct part, and all diodes have been checked to ensure the correct 
part and placement.
Soldering has been checked.
Verified C67, C65, C64, C68, D13, Q18 for value and orientation.
Relays click when changing bands.

Still getting the following readings.
3500 = 8248.42
7000 = 12010.78
10100 = 14157.67
14000 = 16976.67
18068 = 18878.23
21000 = 15211.55
24890 = 16977.38
28000 = 18878.84

I am at a loss for what to look for next. Everything seems to check out, but my 
readings are still off. Anyway I can try to isolate a faulty component?

Sent from my iPad

On 2013-02-02, at 10:38 AM, Don Wilhelm w3...@embarqmail.com wrote:


Jeremy,

I have read your exchanges with Gary,

First, don't bother with the C22 setting - just set it to the midpoint (slot 
parallel with the long edge of the board) and leave it there until you have the 
rest of the K2 receiver working on all bands, and then go to my website 
www.w3fpr.com and do the procedures stated in the K2 Dial Calibration article 
there.

Taking things one step at a time - is the PLL Range correct at TP3? Tap BAND+ 
to bring it to the highest frequency (about 12100 kHz) then tap BAND- to get to 
the lower limit (about 12087 kHz)  Those frequencies can vary by 2 to 3 kHz 
from the target values and still be OK.

Once assured that the PLL Range is correct, then tackle the VFO frequencies.
You do have something wrong there because your frequencies are too low on all 
bands.  That indicates either too much capacity or too much inductance is 
present in the VFO circuit.  Look at the schematic for RF Board sheet 1.  The 
area in question is in the upper right corner - the input side of Q18 - as well 
as the VFO range Select components.

Is T5 wound on a yellow core?  If wound on a red core, it will have too much 
inductance.  Does L30 have a slot across the entire diameter of the tuning 
slug?  It should.
Look at the tops of D23, D24, D25 and D26.  They should have a top shape like 
Q18 and about the same size.  D21 and D22 should have a smaller body profile 
when viewed from the top.  The wider flat side of all those varactors should be 
facing toward the rear of the RF Board.

Your next step is to check the relays K13, 14 and 15.  The white stripe should 
be on the end toward the rear of the RF board.

Examine the bottom of the board for the soldering of those components in the 
VFO and VFO Range Select areas to be certain there are no tiny solder bridges.

If everything is correct, it *should* have close the frequencies listed in VCO 
Table on the Schematic Key page - within 3 to 5 kHz when everything is correct.

73,
Don W3FPR



On 2/2/2013 9:43 AM, JeremyJones wrote:

I'm in the process of building a K2 and am having trouble at the Alignment
and Test part 2.  I've gone through at ton of previous posts here an have
been talking with Gary at Elecraft but no luck so far.  The main issues are
C22 only has adjustment less than 1khz

Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

I did some playing with numbers in the VFO resonant circuit, and I am 
coming to the conclusion that L30 and T5 are not connected together.  If 
my speculation is correct, you will find a break in the PC board or 
something not soldered.
With the K2 upside-down, look at the bottom of L30.  There is a row of 3 
pins.  The leftmost pin connects to the adjacent lead of T5.
Solder a wire across those two points as a test.  Then check the 
resistance to ground at the rightmost end of that row of 3 pins - it 
should be zero.


Let me know what you find.

73,
Don W3FPR

On 2/2/2013 2:48 PM, JeremyJones wrote:

Hi Don,

I set C22 to midway.
PLL @ TP3 is 12099.12 - 12086.32.
T5 is a yellow core, wound with 15 turns red and 4 green. I had to bring it
down to 15 turns as recommended by Gary to get 8253.86khz @ TP1 when tuned
to 4000.10 for the VCO test.  It was around 7694.39 with 16 turns.
L30 is the correct part, and all diodes have been checked to ensure the
correct part and placement.
Soldering has been checked.
Verified C67, C65, C64, C68, D13, Q18 for value and orientation.
Relays click when changing bands.

Still getting the following readings.
3500 = 8248.42
7000 = 12010.78
10100 = 14157.67
14000 = 16976.67
18068 = 18878.23
21000 = 15211.55
24890 = 16977.38
28000 = 18878.84

I am at a loss for what to look for next. Everything seems to check out, but
my readings are still off. Anyway I can try to isolate a faulty component?




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Don,

Checked D19 is n in the secondary menu.  L30 does change frequency. 
Soldering iron is set to 775F.  I'm using one of those illuminated workbench
magnifying lamps to examine my work.  Even still I reflowed the solder on
all joints to be sure.  U6 circuit components are the correct values and
orientation.  U6 pin 5 reads 4V.  Bridged the pins between L30 and T5 and
resistance is 0.  Checked before bridging and it was as well, but wanted to
be sure.

I am at a loss..

Jeremy



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Jeremy,

OK, let's back up to U4 and U6 for a bit. Set the K2 to 7100 kHz and
tell me the voltages at U4 pin 13. U6 pin 6 and U6 pin 7.

You can remove the bridge between L30 and T5.

Also lift one lead of the red winding on T5 and check the resistance
across L30. In the row of 3 pins, resistance between the leftmost pin
and the rightmost pin.

Technical talk - L30 and the red winding of T5 should result in a lesser
inductance than either of them alone. It appears as though you have
only T5 in the circuit. An open winding at L30 would make the frequency
too low - your present condition.
The reason for the request of the DC voltages at U4 and U6 is to
determine if U6 is operating as expected and there is the expected drops
between U4 pin 13 and U6 pin 6.

73,
Don W3FPR

On 2/2/2013 5:46 PM, JeremyJones wrote:

Don,

Checked D19 is n in the secondary menu. L30 does change frequency.
Soldering iron is set to 775F. I'm using one of those illuminated workbench
magnifying lamps to examine my work. Even still I reflowed the solder on
all joints to be sure. U6 circuit components are the correct values and
orientation. U6 pin 5 reads 4V. Bridged the pins between L30 and T5 and
resistance is 0. Checked before bridging and it was as well, but wanted to
be sure.

I am at a loss..

Jeremy

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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

U4 pin13 = 5.029V
U6 pin6 = 5.026V
U6 pin7 = 0.020V

L30 with 1 red lead removed = 0.5ohm



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

That 5 volts at U4 pin 13 is higher than normal, and is the reason you 
do not have any control over the frequency of the VFO.
Make certain the path from the VFO output through C62 to U4 pin 4 is 
intact with good soldering all the way.   Check the value of C62 (0.01 
uF marked 103).  Make certain pins 5, 6 and 7 of U4 are properly 
soldered.  Do the DC voltage checks on U4 and let me know the results.


73,
Don W3FPR

On 2/2/2013 6:42 PM, JeremyJones wrote:

U4 pin13 = 5.029V
U6 pin6 = 5.026V
U6 pin7 = 0.020V

L30 with 1 red lead removed = 0.5ohm



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

C62 is correct, and the path is intact.  Reflowed the solder on all
connections just to be sure.  
U4 readings are as follows
Pin1 = 0.111
Pin2 = 0.339
Pin3 = 0.006
Pin4 = 2.363
Pin5 = 4.99
Pin6 = 4.99
Pin7 = 4.99
Pin8 = 4.99
Pin9 = 0.001
Pin10 = 0.001
Pin11 = 0.000
Pin12 = 0.000
Pin13 = 5.029
Pin14 = 5.029
Pin15 = 5.029
Pin16 = 5.029

Pins 1, 2, 7, 8, 12, and 13 are not within the specs in the manual.  Is this
a bad U4, or should I start tracing backwards?




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

So I started tracing back and checking joints and reflowing solder.  I now
have 0.760 @ pin8, 0.000 @ pin 13, and 0.00 @ pin 15.

R30 is now showing 8.04V, but 40M is reading in the 13000khz range, with L30
able to adjust frequency but not voltage. 

I'm thinking I may need to add back in the turn that was removed from T5
earlier to bring everything into spec? 



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

The DC voltages at U4 pins 1 and 2 are suspicious.  The voltage at pin 5 
is from the MCU digital outputs, so I would not be to concerned about it 
just yet.  However, compare the voltage at U4 pin 5 with the voltage at 
U7 pin 2 - that is the same signal, and the voltages should be the 
same.  If they are not, then there is a connection problem.


If the U7 pin 2 and the U4 pin 5 voltages are the same, I would suggest 
a replacement of U4 may be in order - but first check for a solder 
bridge across C87 - that would drag the U4 pins 1 and 2 voltages down to 
close to zero.


73,
Don W3FPR
On 2/2/2013 7:56 PM, JeremyJones wrote:

C62 is correct, and the path is intact.  Reflowed the solder on all
connections just to be sure.
U4 readings are as follows
Pin1 = 0.111
Pin2 = 0.339
Pin3 = 0.006
Pin4 = 2.363
Pin5 = 4.99
Pin6 = 4.99
Pin7 = 4.99
Pin8 = 4.99
Pin9 = 0.001
Pin10 = 0.001
Pin11 = 0.000
Pin12 = 0.000
Pin13 = 5.029
Pin14 = 5.029
Pin15 = 5.029
Pin16 = 5.029

Pins 1, 2, 7, 8, 12, and 13 are not within the specs in the manual.  Is this
a bad U4, or should I start tracing backwards?




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

You are making progress.
That is a good indication that you have resolved the problem.
Yes, add back turn 16 of T5 and things should come into normal.

Hint - you may still have to spread/compress the T5 windings, but as an 
aide to know which is to be done, tune down from 4000 kHz to where the 
voltage at R30 drops below 8 volts.  Then adjust the turns on T5 to 
reduce the voltage, then re-check 4000 and repeat as necessary.


You will find the maximum voltage will be your 8.04 volts, and you will 
have to change T5 (or readjust L30) to reduce it.  You will not be able 
to see which way to go (compress or spread the T5 turns) with the R30 
voltage at 8 volts, reduce the frequency and then it will become 
apparent whether spreading the turns or compressing them will reduce the 
voltage.  In other words, 'sneak up an getting the 4000 MHz voltage to 
6.00 volts.


Once you have 4000 MHz voltage at 6.00 volts, check the low and high end 
of all other bands.  You may have to make compromises to get all of them 
in range - the 6.00 volts at 4000 kHz is not a hard and fast number, it 
is just a target that usually works.


73,
Don W3FPR

On 2/2/2013 8:52 PM, JeremyJones wrote:

So I started tracing back and checking joints and reflowing solder.  I now
have 0.760 @ pin8, 0.000 @ pin 13, and 0.00 @ pin 15.

R30 is now showing 8.04V, but 40M is reading in the 13000khz range, with L30
able to adjust frequency but not voltage.

I'm thinking I may need to add back in the turn that was removed from T5
earlier to bring everything into spec?




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Thanks Don,

I'll rewind T5 and see where that gets me. 

U4 pins 1 and 2 are still low (no change), and U7 pin2 and U4 pin5 are
equal.  Do you still suspect there may be an issue with U4?



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30


Jeremy,

Since you now have 8 volts at the left end of R30, I would wait and see 
if you can get all the band end R30 voltages into spec with adjustment 
of L30 and the turns spacing of T5.  If so, I would ignore the DC 
voltages at U4 pins 1 and 2.  Those voltages are partially a result of 
just where within the 10 kHz range of the PLL reference oscillator it 
happens to be.


I am glad to hear that you now have it working within a reasonable range 
- good work.


73,
Don W3FPR

On 2/2/2013 9:18 PM, JeremyJones wrote:

Thanks Don,

I'll rewind T5 and see where that gets me.

U4 pins 1 and 2 are still low (no change), and U7 pin2 and U4 pin5 are
equal.  Do you still suspect there may be an issue with U4?




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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30

Rewound T5 and now I seem to be back at square 1.
U4 pin13 is high again @5.029V when tuned to 7100khz.
R30 is back to 0.02V
40M is at 11351.25
L30 still changes frequency.
The VCO test at 4000.10 results in 7794.5 @ TP1.
U7 pin2 and U4 pin5 are both 4.99V.
I think I'll call it quits for tonight and see if tomorrow brings better
luck.  

Thanks for all your help,
Jeremy



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Re: [Elecraft] K2 VCO Alignment only 0.02V @ R30