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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