On Wed, 2008-05-14 at 22:02 -1000, Ken Brown wrote:
> Hi all,
>
> 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.
Seems like I've heard of a malady with the ALC blamed on the diodes. I
have no personal experience about them.
>
> 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?
I don't know for sure, but that's been a common pair of techniques.
>
> Anyone out there poked around in these circuits, and know what the
> voltages really should be?
>
> Thanks for any help,
>
> DE N6KB
>
73, Jerry, K0CQ
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