K2 KSB2: Signal Loss through SSB filters

[Lambs, Dick & Judy]

I'd appreciate help diagnosing loss of signal apparently through the  
SSB filters in the KSB2 board.

Everything was working fine with my K2 Serial # 2195 until I upgraded  
it with new crystal filters and the SSBCAPKT mod to increase the SSB  
bandwidth to 2.6 KHz.

I first replaced the crystal filters in the SSB board and tested it.  
Everything still worked fine.

Then I replaced the caps for the values for the 2.6 Khz bandwidth.  
Upon completion, following alignment with Spectrogram,  I found t I  
lost roughly 40 db when using the SSB OPT filter.  The CW filters  
still work OK.

Other than the signal loss, everything works properly.  On  
Spectrogram, after alignment the graph looks just like the one in the  
instructions "K2 Filter Alignment Procedures" (from the N0SS site).  
I verified that I have the BFO on the correct side of filter center  
for both USB and LSB, SSB signals sound good (but are very weak), and  
the dial frequency is correct.  There is no transmit output on SSB,  
but CW works OK.

I checked many times that I put the correct value caps in the correct  
slots and that there are no poor solder joints or bridges.

I checked resistance to ground around the filter circuits, and there  
are no shorts at crystals or caps.

I verified voltages on U1 as shown in the KBS2 manual,  
troubleshooting section, for both transmit and receive, and all  
values are reasonably close, with one probably not important  
exception.  The exception is U1-28 on  receive/transmit is 5.70/5.64,  
whereas the chart shows it should be 5.6/2.4.

The diode cathode voltages shown in the troubleshooting section also  
agree for CW and SSB filters.

I found an email from Don dated 28 Dec 2006 that indicated low gain  
is likely due to diode switching problems.  Don suggested looking at  
voltage on U1 pins 21 and 22.  My values are correct: With the SSB  
OPT filter, Pin 21 is 6 V and Pin 22 is 0.  For the CW filters, Pin  
21 is 0 and Pin 22 is 6 V.  In SSB mode I do have 6 V on the cathodes  
of D6, D9, D10, D13, and D14.

So I'm thinking the problem is in a crystal or cap.  The only  
practical solution I can see is replace the caps, and if that doesn't  
work, replace the crystals.   Unfortunately, I didn't check the caps  
before I installed them, and it's just about impossible to get them  
out without destroying them.

Thanks for any help.

Dick, K0KK


Dick & Judy Lamb
44 Post RD
Iowa City  IA  52245
Phone [phone]


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[Don Wilhelm-4]

Dick,

If I understood correctly:  You changed the crystals and checked it and
found all was OK.  Next, you changed the caps and afterward it was not good.

If the above is correct, then there is a problem with the caps or your
installation of the caps.  Check them again.

If the diode switching worked before, it should be working now, and the
fact that the CW filters are OK says that at least half of the switching
mechanism is working.  You did not change any of the diodes - but you
did make changes *near* the diodes, so check the entire filter end of
the board for something that you may have inadvertently disturbed.  You
could check the small toroidal RF Chokes, but usually if they are a
problem they will kill receive through both the CW and SSB filters.

It might be wise to have someone else check the capacitor values for you
- often a new set of eyes will find things that you may have overlooked.

73,
Don W3FPR

Lamb, Dick & Judy wrote:

> I'd appreciate help diagnosing loss of signal apparently through the SSB
> filters in the KSB2 board.
>
> Everything was working fine with my K2 Serial # 2195 until I upgraded it
> with new crystal filters and the SSBCAPKT mod to increase the SSB
> bandwidth to 2.6 KHz.
>
> I first replaced the crystal filters in the SSB board and tested it.  
> Everything still worked fine.
>
> Then I replaced the caps for the values for the 2.6 Khz bandwidth.  Upon
> completion, following alignment with Spectrogram,  I found t I lost
> roughly 40 db when using the SSB OPT filter.  The CW filters still work OK.
>

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[Tom Arntzen-2]

Did you remember to take out CB and CN to leave "open"?
If you have the 2,2Khz BW board the shall be removed.
73 LA1PHA Tom

----- Original Message -----
From: "Lamb, Dick & Judy" <[hidden email]>
To: "elecraft post" <[hidden email]>
Sent: Friday, August 10, 2007 11:47 PM
Subject: [Elecraft] K2 KSB2: Signal Loss through SSB filters

> I'd appreciate help diagnosing loss of signal apparently through the  SSB
> filters in the KSB2 board.
>
> Everything was working fine with my K2 Serial # 2195 until I upgraded  it
> with new crystal filters and the SSBCAPKT mod to increase the SSB
> bandwidth to 2.6 KHz.
>
> I first replaced the crystal filters in the SSB board and tested it.
> Everything still worked fine.
>
> Then I replaced the caps for the values for the 2.6 Khz bandwidth.   Upon
> completion, following alignment with Spectrogram,  I found t I  lost
> roughly 40 db when using the SSB OPT filter.  The CW filters  still work
> OK.
>
> Other than the signal loss, everything works properly.  On  Spectrogram,
> after alignment the graph looks just like the one in the  instructions "K2
> Filter Alignment Procedures" (from the N0SS site).   I verified that I
> have the BFO on the correct side of filter center  for both USB and LSB,
> SSB signals sound good (but are very weak), and  the dial frequency is
> correct.  There is no transmit output on SSB,  but CW works OK.
>
> I checked many times that I put the correct value caps in the correct
> slots and that there are no poor solder joints or bridges.
>
> I checked resistance to ground around the filter circuits, and there  are
> no shorts at crystals or caps.
>
> I verified voltages on U1 as shown in the KBS2 manual,  troubleshooting
> section, for both transmit and receive, and all  values are reasonably
> close, with one probably not important  exception.  The exception is U1-28
> on  receive/transmit is 5.70/5.64,  whereas the chart shows it should be
> 5.6/2.4.
>
> The diode cathode voltages shown in the troubleshooting section also
> agree for CW and SSB filters.
>
> I found an email from Don dated 28 Dec 2006 that indicated low gain  is
> likely due to diode switching problems.  Don suggested looking at  voltage
> on U1 pins 21 and 22.  My values are correct: With the SSB  OPT filter,
> Pin 21 is 6 V and Pin 22 is 0.  For the CW filters, Pin  21 is 0 and Pin
> 22 is 6 V.  In SSB mode I do have 6 V on the cathodes  of D6, D9, D10,
> D13, and D14.
>
> So I'm thinking the problem is in a crystal or cap.  The only  practical
> solution I can see is replace the caps, and if that doesn't  work, replace
> the crystals.   Unfortunately, I didn't check the caps  before I installed
> them, and it's just about impossible to get them  out without destroying
> them.
>
> Thanks for any help.
>
> Dick, K0KK
>
>
> Dick & Judy Lamb
> 44 Post RD
> Iowa City  IA  52245
> Phone [phone]
>
>
> _______________________________________________
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>
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[Lambs, Dick & Judy]

Problem solved.  I'd like to report the cause and suggest a signal  
tracing method that might be helpful to someone without much test  
equipment.

First, though, I'd like to thank WA6VNN and LA1PHA for their  
suggestions, and of course thank Don, W3FPR, for his customary fast  
response and detailed advice.

The problem was lack of continuity between a trace on the top of the  
circuit board and the pad on the bottom of the board.  I had damaged  
the board when removing the old parts and cleaning the hole, and it  
was not obvious to me from casual visual inspection.  A  short jumper  
on the bottom of the board to parallel the trace solved the problem.

I found the break with the aid of a separate general coverage  
receiver tuned to the K2 IF frequency.  My test probe was a short  
lead on the antenna jack of that receiver.  I fed a strong signal  
from an oscillator into the K2's antenna terminal and tuned the K2 to  
that signal.  Then I put my probe on the input to the KSB2's first  
crystal and adjusted the oscillator output so that I had a near full  
scale S-meter reading on the general coverage receiver.  Next, I  
worked my way with the probe through the filter network, touching  
each coupling capacitor connection between crystals.  I found the S  
meter on the general coverage receiver dropped to about mid scale  
between the input of X3 and the input of X4.  Sure enough, my  
Ohmmeter revealed a break on the trace at the output of X3.

This approach to signal tracing probably is not new to many old  
timers.  However, it is quick and easy, very sensitive, gives both an  
aural and visual indication that you're actually following the  
signal, and works for those lacking test equipment.  For more serious  
tracing with a general coverage receiver it probably would be good to  
make a real probe, use coax to the probe, and put a small (e.g., 5 to  
50 pf) capacitor in series with the line.

BTW, upgrading to the 2.6 KHz SSB bandwidth, from the original 2.1  
KHZ passband in my older K2, made a dramatic difference in audio  
quality.

Dick, K0KK

> I'd appreciate help diagnosing loss of signal apparently through  
> the SSB filters in the KSB2 board.
>
> Everything was working fine with my K2 Serial # 2195 until I  
> upgraded it with new crystal filters and the SSBCAPKT mod to  
> increase the SSB bandwidth to 2.6 KHz.
>
> _______________________________________________
> 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

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