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K2 PLL reference oscillator range is zero

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David Johnson-4

K2 PLL reference oscillator range is zero

Hello and Happy New Year to everyone.

I have owned K2 serial no. 3980 for about five years and it has worked flawlessly. A couple of days ago it stopped tuning properly. Instead of tuning across a signal, it now acts like a crystal controlled radio that tunes in discrete steps of approximately 10 khz as the knob is rotated.

This same problem was described on this list just last month by Jon, KB1QBZ, and he said that he solved it by redoing the alignment and test steps, part II. So I began by redoing the 4 MHz Oscillator Calibration, which gave me a frequency of 12.086 Mhz.

The next step is the PLL Reference Oscillator Range test, but I got no change in the 12.086 Mhz indication by tapping either the Band + or Band - switch.

So I measured the voltages on U6, and got 0 volts on pins 2, 3 and 4 at all times, with no change as I tapped the Band + and Band - switches. I also got a steady 2.0 volts on pin 7. I know these voltages are supposed to change as you tap the Band + and Band - switches, but is this something that you can see on a digital voltmeter, or is it something instantaneous that you need to view with an oscilloscope?

I backed up and measured voltages on U5. I got 5V on pin 1, and 0 volts on pins 3 and 4, all opposite of what the voltage table lists. I also got 0 volts on pin 7 continuously even when I tapped the Band + and Band - switches.

Finally I looked at the thermistor board, but I wasn't sure quite how to investigate it. I have 1.2 volts at the junction of RA/Rt/RB and 0 volts at the junction of RB and RC.

Are my symptoms consistent with a bad thermistor, or is this more likely to be a failure within U5 or U6?

Sorry for taking up all this bandwidth but I am not sure what my next step should be.

Thank you for any and all suggestions on how to proceed.

-- Dave WB4JTT

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Don Wilhelm-4

Re: K2 PLL reference oscillator range is zero

Dave,

Yes, do check U5, but ignore the voltages on pins 1, 2 and 3 because
they are digital and the active state may not correspond with the
voltage measured with a DMM.
U5 pin 8 must have 5 volts DC for the chip to work - if that is not
true, stop (all other tests are futile).

Next monitor the voltage at U5 pin 7 while tapping BAND+ and BAND-. the
voltage should go to 4 volts or more when BAND+ is tapped and to nearly
zero volts when BAND- is tapped. If that is true, then U5 and its
driving digital signals are OK.

Next thing to check is U6 - check at pin 1. The voltage when BAND+ is
tapped should be near 8 volts and when BAND- is tapped should be near
zero volts. If U5 pin 7 was OK, but this test fails, the fault is
likely with U6 or the thermistor board.

To give a quick check on the thermistor board, measure the voltage at U6
pin 5 - it should be 4 volts (or more precisely, 1/2 of the 8 volt
regulator voltage.

If the U6 pin 1 output is correct, there is not much more to check. R19
should have a similar voltage swing (between BAND+ and BAND-), and the
voltage on varactors D16 and D17 cathodes should be similar.

If all checks out so far, blame X1 or L31.

Remember that since this K2 worked properly before, there should be only
a single failure. Your challenge is to find the source.

73,
Don W3FPR

David Johnson wrote:

> Hello and Happy New Year to everyone.
>
> I have owned K2 serial no. 3980 for about five years and it has worked flawlessly. A couple of days ago it stopped tuning properly. Instead of tuning across a signal, it now acts like a crystal controlled radio that tunes in discrete steps of approximately 10 khz as the knob is rotated.
>
> This same problem was described on this list just last month by Jon, KB1QBZ, and he said that he solved it by redoing the alignment and test steps, part II. So I began by redoing the 4 MHz Oscillator Calibration, which gave me a frequency of 12.086 Mhz.
>
> The next step is the PLL Reference Oscillator Range test, but I got no change in the 12.086 Mhz indication by tapping either the Band + or Band - switch.
>
> So I measured the voltages on U6, and got 0 volts on pins 2, 3 and 4 at all times, with no change as I tapped the Band + and Band - switches. I also got a steady 2.0 volts on pin 7. I know these voltages are supposed to change as you tap the Band + and Band - switches, but is this something that you can see on a digital voltmeter, or is it something instantaneous that you need to view with an oscilloscope?
>
> I backed up and measured voltages on U5. I got 5V on pin 1, and 0 volts on pins 3 and 4, all opposite of what the voltage table lists. I also got 0 volts on pin 7 continuously even when I tapped the Band + and Band - switches.
>
> Finally I looked at the thermistor board, but I wasn't sure quite how to investigate it. I have 1.2 volts at the junction of RA/Rt/RB and 0 volts at the junction of RB and RC.
>
> Are my symptoms consistent with a bad thermistor, or is this more likely to be a failure within U5 or U6?
>
> Sorry for taking up all this bandwidth but I am not sure what my next step should be.
>
> Thank you for any and all suggestions on how to proceed.
>
> -- Dave WB4JTT
>
>

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David Johnson-4

K2 PLL reference oscillator range is zero

Don,

Thanks for the quick response!

I do have the 5 volts on pin 8 of U5, but a constant 0 volts on pin 7 even when tapping the Band + and Band - switches. But I'm just looking at it with a Digital Voltmeter, not a scope so maybe I'm missing it.

Pin 5 of U6 is 4 volts, so at least that data point is OK.

Should I suspect U5 at this point? What can I do to verify that U5 is being properly triggered at its input when I tap the Band + and Band - switches?

Thanks again.

-- Dave WB4JTT

--- On Wed, 12/31/08, Don Wilhelm <[hidden email]> wrote:

> From: Don Wilhelm <[hidden email]>
> Subject: Re: [Elecraft] K2 PLL reference oscillator range is zero
> To: [hidden email]
> Cc: [hidden email]
> Date: Wednesday, December 31, 2008, 2:56 AM
> Dave,
>
> Yes, do check U5, but ignore the voltages on pins 1, 2 and
> 3 because they are digital and the active state may not
> correspond with the voltage measured with a DMM.
> U5 pin 8 must have 5 volts DC for the chip to work - if
> that is not true, stop (all other tests are futile).
>
> Next monitor the voltage at U5 pin 7 while tapping BAND+
> and BAND-. the voltage should go to 4 volts or more when
> BAND+ is tapped and to nearly zero volts when BAND- is
> tapped. If that is true, then U5 and its driving digital
> signals are OK.
>
> Next thing to check is U6 - check at pin 1. The voltage
> when BAND+ is tapped should be near 8 volts and when BAND-
> is tapped should be near zero volts. If U5 pin 7 was OK,
> but this test fails, the fault is likely with U6 or the
> thermistor board.
>
> To give a quick check on the thermistor board, measure the
> voltage at U6 pin 5 - it should be 4 volts (or more
> precisely, 1/2 of the 8 volt regulator voltage.
>
> If the U6 pin 1 output is correct, there is not much more
> to check. R19 should have a similar voltage swing (between
> BAND+ and BAND-), and the voltage on varactors D16 and D17
> cathodes should be similar.
>
> If all checks out so far, blame X1 or L31.
>
> Remember that since this K2 worked properly before, there
> should be only a single failure. Your challenge is to find
> the source.
>
> 73,
> Don W3FPR
>
>
> David Johnson wrote:
> > Hello and Happy New Year to everyone.
> >
> > I have owned K2 serial no. 3980 for about five years
> and it has worked flawlessly. A couple of days ago it
> stopped tuning properly. Instead of tuning across a signal,
> it now acts like a crystal controlled radio that tunes in
> discrete steps of approximately 10 khz as the knob is
> rotated.
> > This same problem was described on this list just
> last month by Jon, KB1QBZ, and he said that he solved it by
> redoing the alignment and test steps, part II. So I began
> by redoing the 4 MHz Oscillator Calibration, which gave me a
> frequency of 12.086 Mhz.
> >
> > The next step is the PLL Reference Oscillator Range
> test, but I got no change in the 12.086 Mhz indication by
> tapping either the Band + or Band - switch.
> >
> > So I measured the voltages on U6, and got 0 volts on
> pins 2, 3 and 4 at all times, with no change as I tapped the
> Band + and Band - switches. I also got a steady 2.0 volts
> on pin 7. I know these voltages are supposed to change as
> you tap the Band + and Band - switches, but is this
> something that you can see on a digital voltmeter, or is it
> something instantaneous that you need to view with an
> oscilloscope?
> >
> > I backed up and measured voltages on U5. I got 5V
> on pin 1, and 0 volts on pins 3 and 4, all opposite of what
> the voltage table lists. I also got 0 volts on pin 7
> continuously even when I tapped the Band + and Band -
> switches.
> >
> > Finally I looked at the thermistor board, but I
> wasn't sure quite how to investigate it. I have 1.2
> volts at the junction of RA/Rt/RB and 0 volts at the
> junction of RB and RC.
> > Are my symptoms consistent with a bad thermistor, or
> is this more likely to be a failure within U5 or U6?
> >
> > Sorry for taking up all this bandwidth but I am not
> sure what my next step should be.
> >
> > Thank you for any and all suggestions on how to
> proceed.
> >
> > -- Dave WB4JTT
> >

David Johnson-4

Re: K2 PLL reference oscillator range is zero

In reply to this post by David Johnson-4

Don and the group,

I have not yet solved this problem, but upon further troubleshooting a recurrent theme seems to be that the clock signal (SCK), which appears at pin 18 of MCU U6, pin 6 of EEPROM U7 and pin 10 of U8 on the control board, as well as pin 1 of DAC U5 on the RF board is constantly 5 volts when, according to the voltage charts, it should be 0 volts.

Further, the /DAC2CS value at pin 19 of the MCU U6 (control board), which is also at pin 3 of U5 (RF board) is 0 volts when it should be 5 volts.

The only other anomalous voltage values on MCU U6 are 0.1 volt on SRDIN pin 33 instead of the listed 5 volts, and 0.2 volt on /SR RD pin 38 instead of the listed 1.2 volts in the chart.

So my question is, what controls the SCK value on pin 18 of the MCU U6? In other words, I assume that there is another pin on U6 that controls whether pin 18 is high or low. If not, should I assume that the MCU is bad because it always reads high?

Many thanks to anyone willing to wade through all this!

-- Dave WB4JTT

--- On Wed, 12/31/08, Don Wilhelm <[hidden email]> wrote:

> From: Don Wilhelm <[hidden email]>
> Subject: Re: [Elecraft] K2 PLL reference oscillator range is zero
> To: [hidden email]
> Date: Wednesday, December 31, 2008, 1:53 PM
> Dave,
>
> Yes, you should suspect U5 (or one of the digital signals
> going into it). No need to look at pin 7 with a scope - the
> output at pin 7 is analog and should remain a steady
> voltage.
>
> Check the soldering of U5 and the /DAC2CS signal path back
> to Control Board U6 pin 19 (there are connectors in the path
> that could also be suspect. The inputs on pin1 and pin 2
> are shared with other digital devices on the Control Board,
> and if you have checked for things like the presence of
> sidetone, those signals (SCK and SDO) are working at their
> source so should be OK although there are also the RF Board
> to Control Board connections to consider as possible faults.
>
> 73,
> Don W3FPR
>
> David Johnson wrote:
> > Don,
> >
> > Thanks for the quick response!
> > I do have the 5 volts on pin 8 of U5, but a constant
> 0 volts on pin 7 even when tapping the Band + and Band -
> switches. But I'm just looking at it with a Digital
> Voltmeter, not a scope so maybe I'm missing it.
> >
> > Pin 5 of U6 is 4 volts, so at least that data point
> is OK.
> >
> > Should I suspect U5 at this point? What can I do to
> verify that U5 is being properly triggered at its input when
> I tap the Band + and Band - switches?
> >
> > Thanks again.
> >
> > -- Dave WB4JTT
> >
> >
> > --- On Wed, 12/31/08, Don Wilhelm
> <[hidden email]> wrote:
> >
> >
> >> From: Don Wilhelm <[hidden email]>
> >> Subject: Re: [Elecraft] K2 PLL reference
> oscillator range is zero
> >> To: [hidden email]
> >> Cc: [hidden email]
> >> Date: Wednesday, December 31, 2008, 2:56 AM
> >> Dave,
> >>
> >> Yes, do check U5, but ignore the voltages on pins
> 1, 2 and
> >> 3 because they are digital and the active state
> may not
> >> correspond with the voltage measured with a DMM.
> >> U5 pin 8 must have 5 volts DC for the chip to work
> - if
> >> that is not true, stop (all other tests are
> futile).
> >>
> >> Next monitor the voltage at U5 pin 7 while tapping
> BAND+
> >> and BAND-. the voltage should go to 4 volts or
> more when
> >> BAND+ is tapped and to nearly zero volts when
> BAND- is
> >> tapped. If that is true, then U5 and its driving
> digital
> >> signals are OK.
> >>
> >> Next thing to check is U6 - check at pin 1. The
> voltage
> >> when BAND+ is tapped should be near 8 volts and
> when BAND-
> >> is tapped should be near zero volts. If U5 pin 7
> was OK,
> >> but this test fails, the fault is likely with U6
> or the
> >> thermistor board.
> >>
> >> To give a quick check on the thermistor board,
> measure the
> >> voltage at U6 pin 5 - it should be 4 volts (or
> more
> >> precisely, 1/2 of the 8 volt regulator voltage.
> >>
> >> If the U6 pin 1 output is correct, there is not
> much more
> >> to check. R19 should have a similar voltage swing
> (between
> >> BAND+ and BAND-), and the voltage on varactors D16
> and D17
> >> cathodes should be similar.
> >>
> >> If all checks out so far, blame X1 or L31.
> >>
> >> Remember that since this K2 worked properly
> before, there
> >> should be only a single failure. Your challenge
> is to find
> >> the source.
> >>
> >> 73,
> >> Don W3FPR
> >>
> >>
> >> David Johnson wrote:
> >>
> >>> Hello and Happy New Year to everyone.
> >>>
> >>> I have owned K2 serial no. 3980 for about
> five years
> >>>
> >> and it has worked flawlessly. A couple of days
> ago it
> >> stopped tuning properly. Instead of tuning across
> a signal,
> >> it now acts like a crystal controlled radio that
> tunes in
> >> discrete steps of approximately 10 khz as the knob
> is
> >> rotated.
> >>> This same problem was described on this list
> just
> >>>
> >> last month by Jon, KB1QBZ, and he said that he
> solved it by
> >> redoing the alignment and test steps, part II. So
> I began
> >> by redoing the 4 MHz Oscillator Calibration, which
> gave me a
> >> frequency of 12.086 Mhz.
> >>
> >>> The next step is the PLL Reference Oscillator
> Range
> >>>
> >> test, but I got no change in the 12.086 Mhz
> indication by
> >> tapping either the Band + or Band - switch.
> >>
> >>> So I measured the voltages on U6, and got 0
> volts on
> >>>
> >> pins 2, 3 and 4 at all times, with no change as I
> tapped the
> >> Band + and Band - switches. I also got a steady
> 2.0 volts
> >> on pin 7. I know these voltages are supposed to
> change as
> >> you tap the Band + and Band - switches, but is
> this
> >> something that you can see on a digital voltmeter,
> or is it
> >> something instantaneous that you need to view with
> an
> >> oscilloscope?
> >>
> >>> I backed up and measured voltages on U5. I
> got 5V
> >>>
> >> on pin 1, and 0 volts on pins 3 and 4, all
> opposite of what
> >> the voltage table lists. I also got 0 volts on
> pin 7
> >> continuously even when I tapped the Band + and
> Band -
> >> switches.
> >>
> >>> Finally I looked at the thermistor board,
> but I
> >>>
> >> wasn't sure quite how to investigate it. I
> have 1.2
> >> volts at the junction of RA/Rt/RB and 0 volts at
> the
> >> junction of RB and RC.
> >>> Are my symptoms consistent with a bad
> thermistor, or
> >>>
> >> is this more likely to be a failure within U5 or
> U6?
> >>
> >>> Sorry for taking up all this bandwidth but I
> am not
> >>>
> >> sure what my next step should be.
> >>
> >>> Thank you for any and all suggestions on how
> to
> >>>
> >> proceed.
> >>
> >>> -- Dave WB4JTT
> >>>
> >>>
> > _______________________________________________
> > Elecraft mailing list
> > Post to: [hidden email]
> > You must be a subscriber to post to the list.
> > Subscriber Info (Addr. Change, sub, unsub etc.):
> > http://mailman.qth.net/mailman/listinfo/elecraft
> > Help: http://mailman.qth.net/subscribers.htm
> > Elecraft web page: http://www.elecraft.com
> >
> ------------------------------------------------------------------------
> >
> >
> > No virus found in this incoming message.
> > Checked by AVG - http://www.avg.com Version: 8.0.176 /
> Virus Database: 270.10.1/1869 - Release Date: 12/30/2008
> 12:06 PM
> >
> >

Don Wilhelm-4

Re: K2 PLL reference oscillator range is zero

Dave,

Your measurement on SCK is correct - the manual is wrong for that one.
If you look at it with a 'scope, you will see negative going pulses when
the clock is active (turn the VFO knob to generate a few pulses.

I believe your problem is with the /DAC2CS signal which I just verified
as 5 volts when measured as a DC signal, but like the SCK signal has
negative going pulses when the VFO knob is turned. Since your K2
/DAC2CS is at zero volts, the DAC is being gated for data-in at all
times, so when the data is not being clocked to the DAC, it thinks the
data bits in the data stream are all inactive, and the analog output
goes to zero volts.

Your readings at U6 pins 33 and 38 are in the range of normal readings.
Pin 38 is active positive and is normally low with frequent positive
going pulses, so the DC voltage measured can vary depending on the time
constant of the meter used, and pin 33 is also active high, being
normally low and having less frequent positive pulses than those on pin
38 - so its DC average voltage will be less than that on pin 38 - how
much depends on your meter.

I don't know if your digital skill level was adequate to follow all of
that explanation, but the bottom line is that something is not working
between the microprocessor (Control Board U6) pin 19 and RF Board U5 pin
3. Go back to CB U6 pin 19 and measure the voltage there - if the
voltage is 5 volts there while being 0 volts at RF U5 pin 3, there is a
break in the path - that includes the CB to RF board connectors - find
the break and fix it (you can verify the fix with a continuity check on
your DMM).
OTOH, if the voltage is zero at both places, the problem is *either* a
bad microprocessor output or a shorted RF Board U5 pin 3. The best way
to determine which it is requires removing U5. If the voltage goes to 5
volts with U5 removed, the microprocessor is good and U5 is bad - but if
it stays at zero volts, then the microprocessor needs to be replaced.

There is another way to check if you do not have de-soldering equipment
and cannot easily remove U5. Remove Control Board U6 from its socket
and insert the ends of a resistor (470 ohms to 2,2k will do nicely for
this check) between U6 pins 11 and 19 (count carefully). Then power the
K2 on (do not expect a display or anything else to happen), then measure
the voltage at RF Board U5 pin 3 - if it is 5 volts, U5 is OK, get a new
K2 firmware chip - but if the voltage is zero at U5 pin 3, replace U5.

73,
Don W3FPR

David Johnson wrote:

> Don and the group,
>
> I have not yet solved this problem, but upon further troubleshooting a recurrent theme seems to be that the clock signal (SCK), which appears at pin 18 of MCU U6, pin 6 of EEPROM U7 and pin 10 of U8 on the control board, as well as pin 1 of DAC U5 on the RF board is constantly 5 volts when, according to the voltage charts, it should be 0 volts.
>
> Further, the /DAC2CS value at pin 19 of the MCU U6 (control board), which is also at pin 3 of U5 (RF board) is 0 volts when it should be 5 volts.
>
> The only other anomalous voltage values on MCU U6 are 0.1 volt on SRDIN pin 33 instead of the listed 5 volts, and 0.2 volt on /SR RD pin 38 instead of the listed 1.2 volts in the chart.
>
> So my question is, what controls the SCK value on pin 18 of the MCU U6? In other words, I assume that there is another pin on U6 that controls whether pin 18 is high or low. If not, should I assume that the MCU is bad because it always reads high?
>
> Many thanks to anyone willing to wade through all this!
>
> -- Dave WB4JTT
>
>
> --- On Wed, 12/31/08, Don Wilhelm <[hidden email]> wrote:
>
>
>> From: Don Wilhelm <[hidden email]>
>> Subject: Re: [Elecraft] K2 PLL reference oscillator range is zero
>> To: [hidden email]
>> Date: Wednesday, December 31, 2008, 1:53 PM
>> Dave,
>>
>> Yes, you should suspect U5 (or one of the digital signals
>> going into it). No need to look at pin 7 with a scope - the
>> output at pin 7 is analog and should remain a steady
>> voltage.
>>
>> Check the soldering of U5 and the /DAC2CS signal path back
>> to Control Board U6 pin 19 (there are connectors in the path
>> that could also be suspect. The inputs on pin1 and pin 2
>> are shared with other digital devices on the Control Board,
>> and if you have checked for things like the presence of
>> sidetone, those signals (SCK and SDO) are working at their
>> source so should be OK although there are also the RF Board
>> to Control Board connections to consider as possible faults.
>>
>> 73,
>> Don W3FPR
>>
>