[TenTec] OmniVI+ 30M L.O. instability

[Steve Hunt]

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 
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
>
>