Hi Jack
When it is very warm in my shack (~85F) my Omni VI+ has the following problem on 30M only.
Every 35 seconds or so the frequency would jump on the order of 10-50Hz for a
fraction of a second, and then return. The symptoms suggest that the 30 meter
L.O. (on L.O. mixer board) is briefly losing lock with the reference oscillator
(on logic board). At elevated temperature, I suspect that Y4 may drift
slightly out of spec; the DC voltage fed back through connector 84 then
corrects the oscillator frequency and regains lock. Perhaps an adjustment of
30M oscillator coil L19 would mitigate the problem.
The thirty meter oscillator seems to be the one that takes the longest
to get locked when switching to that band, and it the one most likely to
drift out of lock as you are describing. Adjusting the coil is likely to
fix the problem. I can help you with an explanation of what to monitor
with a scope, what to look for and how to make the adjustment. You may
be able to find this in the archives.
However, my question is how to access L19 while keeping the 30M oscillator
active. The L.O. mixer board is located under the FM and LL driver/NB boards,
requiring disconnection of cables to access the board.
I know of no other way to get in there. That is how I did it. Beware of
a couple of things. The order of the coils used for each band is
immediately obvious, partly because a few of the crystals and coils are
used on more than one band. You may end up adjusting ones you would have
rather left alone. It is easy to push too hard on the ferrite (I think)
slugs, making them go to the bottom of the coil, and difficult to get
them to unscrew back out. The PCB does not have holes under each coil
slug, so you cannot push them from the back side of the board. You have
to unsolder and unmount the whole coil and can, if you should need to
get to the opposite end of the slug.
I recall some discussion on the forum a while back about a similar 30M
instability problem. I appreciate any suggestions about how to access the L.O.
mixer board, while at the same time keeping the L.O. active.
I don't recall whether I had all boards powered and connected when I
adjusted mine. I think perhaps the FM board was completely disconnected
and maybe the low level driver board too. You don't need them
functioning to get the adjustment done.
If you can't find my description of how Ten-Tec told me to adjust it in
the archives, ask me and when I get the time I'll find it in my email
archives, maybe.
DE N6KB
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