Low or no output on a band or bands can be dirty switch contacts. 10,
12, and 15 haven't had much use in the past few year. It might be a
quarter drop of deoxit on each contact with some vigorous switch
operation might clean them up, or the problem could be a poor solder
joint that went open or nearly open.
The Omni VI uses diode switching for all of that. I don't think there is
a single mechanical switch contact (besides the band select push button)
involved with the band selection. If it indicates that it has switched
to the band you want, then that pushbutton is working fine. The parallel
band select lines that go to various boards may need cleaning and the
bad solder joint is a possibility.
Its not possible to be more specific because there can be so many ways
to loose a band or bands (and the crystal is not above suspicion nor the
crystal socket when crystals are used to heterodyne the VFO) unless one
has repaired many Omni VI with the same problem. I doubt there's any RF
difference between VI and VI+.
Omni VI does not use crystal sockets. A bad crystal, or misaligned
inductor in the crystal oscillator circuit could be the cause. Don't
mess with those inductors unless you have the right equipment to get
yourself out of the trouble you may cause. The locations of the coils
used for each band is not immediately obvious, and there is a good
chance you'll end up adjusting one that did not need adjusting. Make
sure you use the perfectly shaped soft plastic twiddle stick for the
inductor slug or you will likely break the slug. You will need an
oscilloscope with a high impedance probe (like a 10 X probe that only
loads the circuit with 10 Meg ohms + small capacitance) to monitor the
PLL loop in order to properly set those slugs. And when you have that
equipment, the description of the waveform you are looking for is more
than I'm prepared to put in this message.
DE N6KB
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