Phil
Do NOT attempt to realign those passband filters! Normal aging will not
give you a 20 dB signal loss. Alignment can mask other problems and can
compound finding a resolution for your problem. Realignment would problem
require a sweep generator, or at worst, hours of tedious stagger tuning
while manually sweeping the response curves.
A high Z scope is fine, since you are tracing 50 ohm signal paths it will
not load the circuits.
Getting back to your problem: do what Gary suggested. Carefully resolder
all of the connections for the components in that particular filter. You
might want to first verify that the associated switching diodes are indeed
being forward biased when that band range is selected! It could be as
simple as the diodes not being switched on.
I had a similar passband filter failure in LO system. No fun.
regards
Peter k1zjh
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