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.
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