[TenTec] Please help with touchy OMNI - D

[Dr. Gerald N. Johnson]

On Thu, 2010-01-14 at 12:16 -0600, Virginia Smith wrote:
> Hi All,
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> I've had this OMNI - D since 1998, bought from the original owner who had had it serviced prior to sale, however all the time I've had it, the rig has been very "touchy"  The circuit breaker on the 252M power supply trips often.  I was told by a couple of local TenTec users to consult this list, and that it could be an issue with the power supply or the ALC circuitry - which I have never quite understood how to set.  
> 
As posted, could be an overly sensitive breaker, or alc that lets you
over drive the PA resulting in excess collector current, or something of
a mismatch in the output section that lets the PA draw excess current.
Its not out of the question for there to be a bad PA transistor drawing
excess current or a PA bias setting that has the idling collector
current too high. Testing into a dummy load would be a prime test as
that would separate the tuner and its swr meter from the problems. A
faulty SWR meter might present a bad impedance to the Omni D. It may
present the same impedance to the Icom, but because of a different
output filter may not cause the ICOM to draw excess current or the
reflected power protection in the ICOM may make it back off on power to
keep it protected. I can't say what the bad load impedance would be
because its transformed through the low pass filter and other impedance
matching circuitry. And that can be different for different bands and
radios. Its conceivable there is a problem in that circuitry in the Omni
which is why measuring the collector current and testing with a good
dummy load can help separate things as well as allow testing on other
bands to see if its band sensitive.
> 
> FYI, I am on an 88 ft doublet antenna, fed with ladder line on an MFJ antenna tuner.  I can tune at low power, but when I go above a few watts I am operating on the edge of shutdown.  There is no evidence of stray RF, as I get reports of a clean signal when I do get on the air.  
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> Also I am currently using the same antenna/tuner setup on a loner Icom rig, and everything is fine.
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> Any ideas?
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> Thanks
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> 73
> 
> Virginia
> 
> KD5EZN
> 
> ginnieruth at hotmail.com
> 
73, Jerry, K0CQ