Jack,
It's a few months since I had the same problem with my Omni VI on 160m.
If I remember correctly I was able to unbolt the FM and Driver boards
and flip them carefully to one side to get access to the mixer board. I
put a piece of thick paper under them to prevent shorts to the chassis
in their temporary position. I believe there was also at least one lead
I left disconnected from these boards to allow them to "flip" out of the
way, but which had no effect on the basic functioning of the Tx/Rx. It
should be obvious which they are.
There was a useful posting a few months ago on the list about how to
adjust the Crystal. It involved monitoring the pulse width on the PLL
chip. I did mine by monitoring the PLL control voltage, but I did find
that setting it mid-way between the 2 lock points didn't always give
best results. So the pulse width method is probably the way to go.
And as others have said, be careful of those cores - I cracked one, and
then the whole board has to come out!
73,
Steve G3TXQ
Jack Mandelman wrote:
> 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.
>
> If the problem starts occuring more frequently I may want to slightly adjust
> L19 on the L.O. mixer board. 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 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 did
> access the L.O. mixer board to fix an earlier problem related to an L.O.
> output filter, but totally removed the board at that time.
>
> 73 Jack K1VT
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>
>
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