Hi all,
My Omni VI has a cyclical drift problem. It sounds like a PLL drifting
away from lock and then being pulled back into lock over and over again.
My first guess was that one of the crystals or other components on the
XTAL OSC. - L.O. MIXER BOARD had aged to the point where it was
difficult to keep it locked. I was hoping that a minor tweak to the
appropriate slug tuned inductor would bring that oscillator back to a
consistent lock. Then I discovered that it happens on all bands. It is
beyond reason to believe that all ten of the band select crystals and
associated components have simultaneously aged to the point where they
all require an adjustment. So, I must conclude that something common to
all bands has changed.
The problem does not change using different modes (CW, USB, LSB, FSK) ,
so I must conclude it is not a BFO problem (the BFO does not have any
PLL circuitry anyway.
The rate of the cyclical "drift and pull back into lock" rate does
change depending on the band selected. The cyclical rate ranges all the
way from once every 12 seconds (on 40 meters), to nearly two times per
second (on 80, 20 and 15 meters. When I listen to the transmit signal,
it has the same cyclical drift. When I listen to the 20 MHz crystal
oscillator it is solid and stable. When I disconnect the cable from
connector 84 on the LOGIC BOARD, the "drift and pull back into lock"
action stops, and of course the frequency shifts a bit and the XTAL OSC
is no longer locked to the 20 MHz master reference oscillator.
It seems like I could make the problem go away by adjusting all the
coils for each of the band select crystals, however I think there must
be a common fault that is really the cause of this problem.
Anyone had a similar problem with an Omni VI? How did you fix it? Where
is the XTAL OSC. - L.O. MIXER BOARD located. It is not visible from the
top of the rig. Is it on the bottom side, or is it inside that box
sandwiched between top and bottom?
DE N6KB
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