[TenTec] Omni VI frequency jumping/drifting

Thu Jun 28 21:14:43 EDT 2018

Hi Bob,

I may go back and do it by the manual, but I used a slightly different 
method to align the trimmers since my counter doesn't seem to want to 
measure the BFO for some reason. It measures the master oscillator fine. 
Don't know why it doesn't measure the BFO.  I used the tones WWV 
broadcast and the WSJT-X waterfall to set the LSB and USB trimmers.  
They aren't "perfect" but they are or were less than 10 hz off from the 
500 hz and 600 hz tones WWV broadcast and voice sounds right, to me 
anyway, on LSB and USB.  I guess time will tell if it's really "fixed" now.

Thanks everyone for your help!

73

Stan
KM4HQE

On 06/28/2018 07:56 PM, Bob McGraw K4TAX wrote:
> Regarding adjusting the BFO oscillators, be sure and follow all of the 
> sequence of steps as outlined in the manual.   There is interaction 
> between the adjustments and the modes, so you may have to adjust  2 or 
> 3 times.    Also be sure the radio is on for at least 1/2 hour.  I 
> generally attach my probe to the test point and to the counter and 
> then lay the cover back in place.   Remove the cover and adjust the 
> trimmer for the frequency and mode and then lay the cover back on and 
> observe the counter.  All of that circuit seems rather temperature 
> sensitive.
>
> 73
>
> Bob, K4TAX
>
>
>
> On 6/28/2018 6:07 PM, Stan Gammons wrote:
>> 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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