There is a CW wave shape adjustment on the bottom side. That might be
adjusted incorrectly. It really takes a scope to do this but it seems you
have the knowledge and equipment to do so.
As to the RF distorted audio, sounds like RF into the audio. Works OK at
low levels but distorted at 100 watts. I seem to recall that the Heil mod
adds gain to the mike circuit. This make it more susceptible for RF in the
audio issues.
This Aux audio input is really just another input to the mike audio circuit.
Don't try to use both at the same time. Only use/connect one input at a
time. Also, attenuate the level at the radio and not at the soundcard end
so the level on the cable is as high as possible. Then attenuate at the
radio. I've found this method to work better.
Be sure there is a hard ground between the radio and the power supply
ground. Do not rely on the DC power cable and connectors for ground between
the radio and power supply. Also check to see that the ground terminal at
the radio, specifically inside is tight. The DC connector negative is
connected to this terminal inside the radio.
Be sure the Speech Processor is OFF.
I might have more notes in my service manual, but for now, this is all I can
think of.
73
Bob, K4TAX
----- Original Message -----
From: "Mike" <mike@n1mb.com>
To: <tentec@contesting.com>
Sent: Thursday, June 20, 2013 12:23 PM
Subject: [TenTec] Omni 6 Plus Distorted Audio
Hello Everyone,
I researched all of the threads before posting. I recently purchased an
Omni VI Plus that has the SMT boards. It has the 2.8 Khz Inrad Filter as
well as ALL of the other filters for CW.
When I got it there was severe chirp and key clicks. I spoke with TenTec
about this and they suggested that I look at the DC board which I did and
found connector 5 unplugged. I reattached this connector and 95% of the
chirp was gone as was the key clicks. I looked at the cw waveform before
and after and the difference was substantial.
TenTec had worked on this unit a month before I bought it and gave it a
clean bill of health and indicated that there is a Heil mod on the TX
Audio board. I looked at the schematic for the 564 which indicates that
resistor R54 should be 47k and that R55 should be 100k. TenTec said the
Heil mod changes the resistors R54 to 22k and R54 470k. My unit has the
factory resistor values of 47k and 100k. So it really didn't have the Heil
mod after all. They recommended a 330 k for R55. If you look at the 563
model it has the 330k resistor but not the 564. So I wonder if there was a
reason for dropping the value of R55 from 330k to 100k between models?
On the 9Mhz filter board there is a mod changing C37, C47 and removing the
2.2M resistor. It looks like a suggested mod from W9AC. I changed these
values back to factory specs and the only thing that changes was the CW
waveform wasn't as nice as was with the mod, so I went back with the mod
components. I do not physically see other modifications to the unit.
The signal coming out of connector 79 from the low level driver board
monitored on a second receiver and scope indicates clear undistorted
audio. However, when I reconnect to the finals everything is distorted. I
tried both methods of adjusting the bias, the one in the 564 manual and
then the VE1CHS method to no avail. The PA will produce full 100 watts of
power into a dummy load and the CW mode seems to be working fine with only
a faint hint of chirp when tuned to the 16th octave.
Is there anyone familiar enough with this particular model that could shed
some light on the distorted audio given that I have the mic gain set to
just below where the ALC light flickers and have tried all power settings
and mic settings and a total of 3 different mics. I also connected it to
FLDIGI to see if I could work PSK31 with another ham a few miles away and
he could not decode. He further indicated that it looked like I was over
driving the audio. I placed a voltage divider of 100k inline and 10k to
ground to the sound card audio and varied the audio with the sound card
control as well as the Omni 6 + audio gain control. It was still distorted
even when the output was all the way down to 5 watts.
I would appreciate any information.
Thanks,
Mike
N1MB
ps I have owned several of these units and this is the only one that
exhibits this problem.
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