[TenTec] Omni VI+ Intermittent Power Amp?

[Denton]

Check the dc power plug...and the dc B+ path...fuse, wiring, etc..to the 
finals.
----- Original Message ----- 
From: "Peter Hoon" <peter at nednet.net>
To: "Discussion of Ten-Tec Equipment" <tentec at contesting.com>
Sent: Sunday, March 11, 2007 5:55 PM
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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