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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