[TenTec] Omni VI+ Intermittent Power Amp?

[John T. Fleming]

Peter,

I have two things to suggest, but you may have already tried them.

When I had my Omni D, I had trouble with an intermittent power level
problems.  First, I took two pliers and made sure that all of my coax
connectors were tight.  I was surprised, some were not.  The second item was
the center conductor on the SO-239 on the back of the rig.  I don't know if
I had used a fat soldered PL-259 center pin, but the prongs on the SO-239
center conductor were spread.  I used a jeweler's small screw driver and
bend the prongs back toward the center.  The rig is still running great
today and I grandson is using it.

Good luck and 73,
John

-----Original Message-----
From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
On Behalf Of Peter Hoon
Sent: Sunday, March 11, 2007 8:55 PM
To: Discussion of Ten-Tec Equipment
Subject: [TenTec] Omni VI+ Intermittent Power Amp?

Fellows,

Have you got suggestions for the case of intermittent power out from an Omni
VI Plus?

First year (May 2006 - March 2007) since I am the second owner, no
intermittent noticed; always got full 100 watts on all bands (10 M a little
low, around 90 W out).

Now in second year of ownership.  Very clean unit; complete and successful
receiver alignment matches ARRL MDS.

Suddenly, while operating on 40M CW, into perfectly 1:1 tuned loop via
Dentron tuner, can only get 7 to 9 watts out max on all bands.

Next day, try again, and get full power again on all bands for next 5 days.
Completely normal operation.

Hook to 300 W dummy load on bench.

Adjust bias pots to confirm linear class AB  output on SSB; Speech sounds
fine on adjacent receiver after adjustment; normal full power out after bias
pot adjustments.

All of a sudden, with no changes anywhere, can only get 7 to 9 watts out
again for next 24 hours.

Thinking it might be thermal, wait overnight for cold transceiver.  In
morning, cold, only 7 to 9 watts out. Two tries, same low power result.

Remove power amp module from rear.  Remove blue T wire and coax input from
jack 79. Careful inspection of top circuit board, shows no loose screws,
finals are clean, no obvious cold solder joints; replace blue wire and coax
input.

I have MRF 454 finals.  Throughout testing, heat sink is hardly even warm to
touch.  Power meter on Dentron tuner and on Omni VI Plus match each other;
not a measurement problem.

Turn power out-put pot, front panel,  from min to max, and only 7 to 9 watts
out.

Turn power output pot back to min again, move up to max, and bingo,
completely normal 100 watts out on all bands!

There were no changes.  What the heck is going on!

Would like to know if anyone elase has experienced this kind of transmit
intermittent with an Omni VI plus.  What did you find was the cause?

Am about to go back up and wiggle some more components and wires.

May also remove power amp circuit board and check the underside for cold
solder joints.

Thanks for suggestions and ideas; will report findings for posterity.

Peter
VE1CHS
Nederland, Colorado

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