[TenTec] Omni VI frequency jumping/drifting

[Stan Gammons]

Well, after tweaking C31 to try to get the 10 Mhz signal closer; it 
seems to be more or less behaving now...  The jump on 30 meters is gone 
even though I was unable to get the lock signal to match the other 
bands.  The 160 meter coil had to be adjusted in order to get the lock 
signal to be stable.  So far, FT8 signals on 40 meters is decoding every 
time.  Looks like the BFO trimmers need adjusting though.  When I flip 
between LSB and USB while tuned to WWV, the tone changes. Looks like 
it's about 30 hz off on LSB and about twice as much on USB. Adjusting 
those is kind of a pain since they seem to interact with one another :(


73

Stan
KM4HQE


On 06/28/2018 05:23 PM, Stan Gammons wrote:
> Hi Gary,
>
> I have the 10 Mhz signal. It seems to want to flop between 10,000.000 
> and 10,000.001 to 10,000.002 at times.  For some reason it kills the 
> receive when I connect the counter, a Leader LDC-823S, to pin 9 of 
> U12.  I have to turn the rig off and back on to get the receive to 
> work again.
>
> I take it U13 is the MC145170P1 chip next to connector 88?  If so, it 
> looks like I have 160 meter problems since the signal on pin 11 is 
> there for a fraction of a second, then it's disappears and reappears.  
> On all of the other bands, except 30 meters, the waveform looks nearly 
> the same.  On  30 meters the waveform is wider.  I haven't tried 
> adjusting the coil to see if I can get 30 meters to match the other 
> bands.  Strange thing though on 30 meters is FT8 still decodes even 
> though it jumps about 100 hz for a very brief time.  I'll try 
> adjusting the coil and pulling the board to see if it has any bad 
> solder joints.  Still need to clean the connectors like Bob described 
> in another post.
>
>
> 73
>
> Stan
> KM4HQE
>
>
> On 06/28/2018 08:40 AM, k4mt1950 at charter.net wrote:
>> Stan:
>> I have had the exact same problem with my Omni VI. There is a
>> procedure to properly adjust band crystals. It is:
>> Omni VI Lock PulseRig should be on for at least 1/2 hour.Check 10MHz
>> REF at pin 9 of U12.Adjust 10MHz REF with C31.Check for lock pulse at
>> pin 11 of U13, Scope probe on x10 position; .2 volts per div, and .1us
>> time/div.Adjust L12 thru L21 on Xtal Osc. LO Mixer Bd. for the
>> narrowest wave form.
>> I did this but it did not help. I tuned in WWV and watched it on a
>> waterfall and you could see carrier drifting back and forth. I was
>> missing over half of the FT8 decodes as a result.
>> What I found is PLL circuit on logic board is very temp sensitive. I
>> tried to locate a part but the entire thing is that way. I found by
>> putting a very small fin blowing across logic board completely
>> eliminated the drift cycling.
>> FT8 now works perfectly. Put the fan along the right side (looking
>> from front) and not back panel. Back panel heats up during TX and when
>> I put my fan there the problem got worse when I went into TX.
>> Afraid its a design flaw and cant be fixed any other way.
>> Gary K4MT
>>
>>     -----------------------------------------From: "Stan Gammons"
>> To: "Discussion of Ten-Tec Equipment"
>> Cc:
>> Sent: Wednesday June 27 2018 7:38:42PM
>> Subject: [TenTec] Omni VI frequency jumping/drifting
>>
>>   Hi Everyone,
>>
>>   My Omni VI has decided to throw a few more fits. First the frequency
>>   jumped on 30 meters, but FT8 signals still decode fine. So I let it
>> go
>>   and didn't mess with it. Lately 40 meters has started throwing fits
>> and
>>   it's much worse than 30 meters. Looking at the FT8 waterfall, at
>> times
>>   it will drift during the 15 seconds and it's bad enough the FT8
>> signal
>>   won't decode. I sent another email to the list with the waterfall pic
>>
>>   attached, but the message was too large and got rejected. I tried
>>   tweaking the coils on the crystal oscillator board. It might have
>>   helped 30 meters a little. Doesn't seem to have done much/anything
>> for
>>   40 meters though. Crystals gone bad maybe? If so, anyone know a
>> source
>>   now that ICM is no more?
>>
>>   73
>>
>>   Stan
>>   KM4HQE
>>
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