Ken,
There are some SMD op-amps in the Omni VI ALC circuit that are very
susceptible to static damage. When there is static damage the symptoms can
be similar you yours. Also PIN switching diodes can be damaged by static
and affect the receiver sensitivity.
As I recall it is an easy fix to replace the op-amp but the SMD traces are
VERY fragile. Finding the damaged PIN diodes is a little more challenging
and requires a lot of trouble shooting to determine what band(s) are
affected.
If you are not a DIY kind of guy than Ten Tec factory service is quick and
top-notch.
Good Luck,
Bill - K6WLM
----- Original Message -----
From: "Ken Brown" <ken.d.brown@hawaiiantel.net>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Thursday, May 15, 2008 12:02 AM
Subject: [TenTec] Omni VI problems, need help
> 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.
>
> 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,
>
> DE N6KB
>
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