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

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] OmniVI+ 30M L.O. instability
From: Steve Hunt <steve@karinya.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 31 Aug 2008 08:38:06 +0100
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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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