I am having some difficulties with my Omni VI. The first noticed problem
is low TX power, particularly on 160 meters.
The power is near enough to 100 watts on 80, 40, 30, 20 meter bands that
I would probably not have noticed the problem if I did not operate 160
meters regularly. Even on 160 meters, the power output is nearly full
100 watts above 2.3 MHz, but down around 1800 kHz, where I operate, I
can scarcely get 55 watts out. The power is also low on the higher (15
meters and up) bands. The DC supply to the rig checks out fine, dropping
to about 13.2 VDC after the fuse during key down, and about 12.8 at the
PA supply lead during key down with PWR pot at max.
The ALC LED turns on even with the TX PWR pot set to minimum. It does
this on all bands. The ALC LED remains on at any PWR setting, except on
160 meters it goes out at the high end of the PWR pot range. Due to this
anomalous action of the ALC LED I am suspecting the low TX power may be
due to a malfunction in the ALC.
The T voltage on the Low Level Driver Board is only about 9.7 V to 10.1
V (depending on PWR setting), versus 12.5 V the manual says it should
be. R is about 8.3 V (manual says 8.5 V) and +REG is 9.6 (manual says it
should be 8.5 V). These voltages are off enough that I wonder if the low
level drive stages aren't working up to par because of it, or the ALC
circuit is not working right because of it.
I am reading the circuit description of the L.L. Driver board, where
these voltages come from, and the description of the +REG supply circuit
just can't be right. Says it uses U1 and Q19. Looks like U4 and Q19,
except there are two U numbers inside the dashed lines for that IC. Then
it says something about Q11, but must be a typo, because Q11 is part of
the NB circuit, not part of the regulator. Maybe the voltages listed are
typographical errors too. I also do not see a single ground reference
lead to this board, other than coax shields. I have tightened the
mounting screws on this board. Is the mounting screws and the coax
braids the only way a ground reference is provided to this board?
Anyone out there poked around in these circuits, and know what the
voltages really should be?
Thanks for any help,
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