[TenTec] OMNI VI+ problem

Don Rasmussen wb8yqj at yahoo.com
Fri Mar 11 11:24:50 PST 2011

Hi Guys,
My OMNI 564 started acting a little odd today, I thought I would see if anyone has any suggestions as far as things to consider before packing the unit up for shipment to the factory for service. 
What happens is, when the radio is started from cold at 28.400 everything is normal listening on SSB. After some time, the VCO will seem to lose lock and we lose receive audio and no transmit. This will come and go for 30 minutes.
If I arrow up 100KHZ the radio will return to a normal state. If I dial back down towards 28.400 the radio will tune normally until it gets somewhere near 28.440 where it will go silent. 
That is to say after the radio went silent at 28.400 and I tune up to 28.480 it would remain silent. However, if it went silent at 28.400 and I arrow up or tune up 150 khz and then tune back down, when I arrive at 28.480 the radio will be working.
I was looking at the L.O Mixer board (page 4-14 in the manual) and I can see where there are 10 crystals and one would be selected at 28.0, 28.5, 29.0 and 29.5 so maybe we have a marginal crystal in the 28.0 position. However I wonder why the crystal is okay at 28.475 all of the time and failing at 28.400. You would assume the crystal would fail up until the 28.500 point where the next crystal in sequence would be selected. 
There is a variable inductor at L17, wondering about that one. 
All of the other bands and frequencies work 100%, just this one small bugaboo in this one spot and so far only when the radio is cold. 
Any ideas on things to check would be welcome. 
Don wb8yqj/6

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