[Elecraft] K2 KSB2: Signal Loss through SSB filters

[Tom Arntzen]

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" <rlamb at slamb.org>
To: "elecraft post" <Elecraft at mailman.qth.net>
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 319.338.2721
>
>
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