[TenTec] OMNI VI VXCO help needed DK5AD

[Dr. Gerald N. Johnson]

On 4/4/2010 10:01 AM, knut.baczko at t-online.de wrote:
>
> Hello,
> hopefully somebody is able to help me.
> I have an OMNI VI, model 563. Since some time there was a chirp on 17m
> and 12m did not work at all.
> I checked the 10.000MHZ reference frequency form the crystal oven at
> connector 88 and it seemd  ok.
> Anyhow I wanted to test and turned trimmer capacitor 31. This had no
> frequency effect. At that time I did not know that I have already  the
> VXCO installed by TT when the rig was at the factory several years ago.
> But after changing capacitor 31 the follwing happened what I dont
> understand at all.

Everything is based on the 10 MHz reference directly or indirectly. What 
I think you have done is messed up the 10 MHz multiplier and so killed 
the synthesizer.

What you needed to have done was to have adjusted the individual band 
crystals that were chirping or not working well on the crystal 
oscillator board, but ONLY 17 and 12 meter, no others. Typically there's 
an analog voltage from a pll that you adjust the crystal coil to center 
that voltage in its working range, probably 2 or 3 volts. I don't have a 
563 manual to know what the effect of C31 is. But first you have to get 
the radio back working by finding the original position for C31, and 
then you can fix the individual boards.

73, Jerry, K0CQ

After switching off and on again, no signals could be
> heard on any band. A complete reset did not help. Only when one switches
> the rig and power supply off for several hours and back again the
> receiver seemed to work ok. But on transmitting in CW I got reports that
> my tone was very bad. I checked my transmitted signal with an
> oscilloscop and it looked ok. What I found out later was that the Omni
> was receiving but only on one frequency depending on the band chosen
> despite that the frequency readout changed when turning the VFO knob.
> For more testing  I tuned capacitor 31 again. After that  I am stuck now
> i.e. the receiver wont tune at all to a different frequency even after
> the rig is switched off for longer time.
> For further information it looks like that at TT the original crystall
> oven was disabled by removing resistor R2 (150 OHM) which carries its
> supply voltage. What I dont understand is why capacitor 31 still seems
> to have a fuction though the oven is disabled? Why does it take so long
> that the receiver is working again when the power is swiched off
> completely? Why is the transmitted signal so bad? And off course what
> can be done to have the OMNI working again.
> I still  like the OMNI VI very much because in the past it was the most
> reliable rig especially in contests. Other newer more computerized rigs
> have sometimes problems with the high transmitted HF power present in my
> shack.
> Knut DK5AD/OE2BZL
>
>