[TenTec] Omni VI audio problem

[Bob McGraw K4TAX]

Stan:

First I suggest turning the speech processor OFF and forever leave it 
OFF.    If you want to use it, just remember,  more is worse.

Even though the mikes worked on the TR7, I view this is no indication 
the wiring is correct for the Omni VI.  I suggest checking the manual 
for the correct mike wiring and physically confirm the mike of choice is 
wired correctly.    I find mike wiring standards to be as varied as dust 
particles in a Texas sandstorm.

Pin #1 is mike high or mike audio

Pin #2 is ground and shield.  Be sure the shield of the mike cable also 
folds back into the Amphenol cable connector to make contact with the 
shell.

Pin #3 is PTT

Pin #4 is  +4 DCV for use with an Electrect mike.

Check the plug in filters on the bottom to see they are seated correctly 
and correct location.  Again, contact cleaning of their pins might be in 
order.

One other test, disconnect the mike, turn the MIC gain fully 
counterclockwise {off}, transmit and listen to the radio.  With the 2nd 
receiver, tune across the frequency and listen for carrier.  In general 
all should be quiet.  If you hear significant carrier, there is a 
procedure to null the carrier.  Probably need an oscilloscope and dummy 
load to do that.

Next would be to check the frequency of the BFO crystals.  Again there 
is an alignment procedure.  This must be adjusted in the exact steps 
outlined in the manual as there is interaction between the adjustments.  
Repeat the procedure a couple of times.   A frequency counter is 
required for this adjustment.  Don't skip one step just because you 
don't intend to use that mode.  There is interaction between the 
adjustments.

And of course my last suggestion, which normally is my first 
suggestion..........take time to pull each cable, using a Q-Tip 
moistened with contact cleaner, scrub the male pins of each and every 
connector.  Then plug and unplug the connector  a couple of times so as 
to wipe the female contacts. Do this one at a time and double check to 
see each connector is inserted fully and correctly.

NEVER NEVER NEVER spray anything into the radio.   {One fellow I know 
[not me] removed the plugin IC's, sprayed into their sockets, and now he 
has a radio full of issues and weirdness.   Remember contact cleaner is 
used to promote the flow of current.   Imagine what takes place in a 
logic IC socket that is wet with cleaner. ugh!!!! }

With a radio of that age, it not at all unusual for the electrolytic 
caps in the audio stage to deteriorate.  One issue which can exist is 
the output of a stage can drift negative a few millivolts.  In effect it 
will reverse polarize the coupling capacitor.  The result is after time 
the 1 MFD cap will migrate to about 0.01 MFD.  Not a good path for audio 
in these circuits. Makes the radio sound funny too.     I always replace 
the audio coupling capacitors with nonpolar electrolytics of the same 
voltage and C value.   There is no need to change parameters. Problem 
solved.  I had a lengthy discussion with Tentec management and 
engineering on the subject some years ago.   It almost caused me to not 
buy a new Omni VI Plus.    Finally, I did and loved it.

Hope this helps.

73

Bob, K4TAX


On 9/17/2018 8:00 PM, Stan Gammons wrote:
> Hi All,
>
> I was tinkering with an old D-104 T-UG8 that I had put a Heil 
> conversion kit in since the original element bit the dust. I ask for 
> an audio report from some of the locals that know what I sound like 
> and they said I sounded terrible.  So, I switched to the Ten-Tec 707 
> mic, same report. So, I tried my trusty old EV-638. Same story.  I 
> didn't try it with the converted D-104 to see what it sounds like. 
> They initially told me it sounded like the mic was picking up 
> something like a fan maybe, so turning the gain down helped a little 
> but not a lot. SO, today I decided to put the Omni VI on a dummy load 
> and listen to it with my Drake TR7.  Yuck! The Omni VI sounds 
> terrible!  It's almost like there is a little bit of a carrier and it 
> has what sounds like digital hash on it. It gets worse the higher the 
> mic gain is cranked. When I modulate, the audio sounds all distorted. 
> Even without modulation, if I turn the processor on and crank it up, 
> the digital hash in the audio seems to get even worse. SO, just to 
> make sure it wasn't something weird going on, I did the same thing 
> with the TR7.  I put it on a dummy load and listened to it with the 
> Omni VI. I tried it with the same mics and the audio is clean. No hash 
> or anything.  Anyone heard of a problem like this with an Omni VI?
>
>
> 73
>
> Stan
> KM4HQE
>
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