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This fix, from Peter, KD7MW, worked great on my OmniVI, which now works
like it should do on 30m. 73 de Mike, ZL1MH.
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Message-ID: <35D5437E.2AB@xtra.co.nz>
To: <tentec@contesting.com>
Date: Sat, 15 Aug 1998 20:14:54 +1200
From: mike hutchins <zl1mh@xtra.co.nz>
Reply-To: zl1mh@xtra.co.nz
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To: "Peter A. Klein" <pklein@seattleu.edu>
CC: tentec@contesting.com
Subject: Re: [TenTec] OmniVI 30m freq jump
References: <3.0.5.32.19980813225648.0079d150@chopin.seattleu.edu>
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Peter A. Klein wrote:
>
> Mike Hutchins <zl1mh@xtra.co.nz> wrote:
>
> >My OmniVI jumps fractionally (high) in freq on both tx & rx on 30m only.
> >The jump occurs every couple of seconds (not too regularly), & does not
>
> Mike: I had this problem, and fixed it with the following advice from
> Ten-Tec. Evidently, if some Omni VIs are calibrated perfectly on 30m, the
> crystal is pulled just outside its stable range. So it tends to drift
> towards where it wants to be, and then snap back into "lock." The fix
> involves putting the crystal where it's content to stay on frequency, even
> if it's a few tens of Hz off exact calibration. Here's the procedure, as I
> posted to the list in Feb. 1998. Hope this helps!
> -----------------
>
> Some time back I reported that my Omni VI had a periodic frequency shift
> on 30 meters. Every 25 seconds or so, the received frequency would jump
> about 100 Hz higher in pitch, and then slide back to where it had been.
> Someone else mentioned having seen this tendency in other Omnis, and
> Steve asked me to document how I fixed it.
>
> I finally got to do the procedure that Ten-Tec service recommended, and
> I'm happy to report that it did clear up the problem.
>
> As described by Ten-Tec service, the periodic frequency jump is due to a
> crystal oscillator that has been adjusted a little too far to lock in
> properly. The fix is to tweak L19 on the "Xtal Osc./L.O. Mixer" board
> 1/4 turn in whichever direction eliminates the problem.
>
> Warm the radio up for at least 1/2 hour. Turn it off and remove the top
> cover. Looking down at the top of the Omni VI with the front panel
> toward you, the oscillator board is in the left front quadrant of the
> radio. To get at the oscillator board, you have to remove the aluminum
> cover on which are mounted two other boards.
>
> Disconnect whatever connectors you have to so that the cover can swing
> out of the way. Draw a sketch of what you've disconnected with the
> proper number/letter of the connector to facilitate getting everything
> back together again. The Ten-Tec tech said to "rotate the cover to the
> right." I found it easiest to flip the left edge of the cover up and
> over to the right side of the radio. He also said that I could leave
> the radio on, but I was a bit nervous about having connectors flapping
> about and possibly shorting to ground while I worked.
>
> Once inside, you'll see a bank of crystals along one edge of the
> oscillator board. Each crystal has a small slug-tuned coil next to it.
> L19, the 30m coil, is the third from the right. The diagram is on page
> 4-25 of the Omni VI manual, but the picture is upside down from the way
> you're looking at the board. Turn the coil 1/4 turn clockwise. Replace
> the cover, and reconnect the connectors, but don't screw in the screws
> yet. Turn the radio back on, warm it up for a couple of minutes, and
> see if the problem has been fixed. If not, remove the cover again, put
> the slug back where it was, and turn it a 1/4 turn counterclockwise.
>
> Counterclockwise did the trick for me. I went a little more than 1/4
> turn. The radio now reads 10.000.04 when the carrier is tone-matched
> with the CW sidetone in CW mode, or in SSB mode when the Omni's audio
> tone-matches another receiver tuned to WWV in the AM mode. So I now
> have a 40 Hz error (BIG DEAL!), but the frequency is stable. Next time
> I'm in the radio, I may back the slug off 1/8 turn and see if it stays
> fixed with less error. For now, I'm happy.
>
> The preceding is provided as a helpful hit for fellow Ten-Techies. I am
> not a professional repairman, nor do I play one on TV. Batteries not
> included. Your mileage may vary. Void where prohibited. So there :-)
>
> 73 from KD7MW
>
> : -----==3== --- ---
> - Peter - : | | | | | | | |
> : @| @| @| @| @| @| @| @|
The above fix was done in just a few minutes, and worked great on MY
OmniVI, which is now like it should be on 30m. Good luck, 73, Mike ZL1MH
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