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[TenTec] Comments on "Repairs"

To: Tentec <tentec@contesting.com>
Subject: [TenTec] Comments on "Repairs"
From: Robert & Linda McGraw K4TAX <RMcGraw@Blomand.Net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Sun, 27 Nov 2005 22:44:25 -0600
List-post: <mailto:tentec@contesting.com>
Here goes........have patience with my probing.

What type of power supply you using?  It should current limit at about 20 
amps. A 30 to 40 amp or higher rated supply can allow the radio PA to draw 
excessive current and damage will result under certain condition where the 
PA load impedance is very low.  Fuses simply aren't fast enough to protect.

Is your power supply protected for over voltage?   It should be and should 
shut down at 15.0 volts.

Is the power supply negative connected to the chassis of the Omni via a 
separate ground and not just the negative power lead?  It should be.

Is the power supply negative connected to chassis of the power supply?  Some 
power supplies {name with held} float the negative and are prone to RF 
getting into the voltage sense circuit and allowing an oscillation to take 
place in the supply.  Can spell trouble for the radio.

Are all pieces of station equipment connected together back to a common 
point such as the power supply via separate dedicated ground  cables. 
Should be.

Regarding the tuner, do you use the radio to adjust the match or do you have 
a bridge like and Autec or MFJ to set the match?
{The best antenna tuner that money can buy, used incorrectly, is no better 
than a cheap tuner.}

Is the meter used to measure SWR in the tuner, or an external meter, or the 
one in the radio.  Coax cables between the devices can cause the SWR to look 
good at one place and produce a very poor match at another location in the 
system.  This can be due to a bad cable or poor connector installation or 
loose connector on the SO-239.

In my case I use a 238 tuner with its internal SWR/Power meter, a Daiwa 
CN-801 SWR & Power meter, and the SWR meter in the radio.  In adjusting the 
tuner I switch in and use an MFJ antenna bridge.  Then switch the radio into 
the system.  In all cases, with power, all three SWR indicating devices will 
show the same and correct SWR reading.  I have seen installations where SWR 
at 3 places will be different.  This indicates circulating RF and that can 
give false SWR indications.  Hope you don't have this condition.

Parts for the Omni VI and VI Plus are basically "off the shelf" parts.  Be 
assured that Tentec Service is fixing the radio, taking it through a 24 hr 
burn-in and it is working when it gets to you.  Hate to say it, but 
something in your station or your method of tune-up is causing a problem.

Get me some more information and I'll dig into it further.

73
Bob, K4TAX
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