Re: [TenTec] Omni C Questions ( Maybe OT )

["Dr. Gerald N. Johnson" <geraldj@weather.net>]

The power switch does nothing in the radio, just goes to the power 
supply connector on the back. Momentary contact switches are unusual on 
the gain control. Might there be a bug in the works literally?
The Omni C oscillator mixer board is mostly equivalent to that for the 
Corsair, but different in the details of filtering, mixer chip, and 
amplification. The same crystal works for 10 and 28.0 MHz bands. Solder 
connections, or crystals having been shaken out of sockets in shipping 
could be the problems. And a strong blow on the gain control shaft from 
inadequate packing could have wrecked the power switch.
If there's no power output on SSB without voice, its not a carrier 
balance problem or audio hum. I don't see any mode dependent connections 
on the PA bias board to make idling current different on SSB than on CW. 
There is a wire grounded only on CW, but its setting time delay on the 
TR relay for external gear. Its more like unbalance in the TX mixer but 
that should not be dependent on mode. Where the mixer drive is higher 
than the output frequency and so blocked between the PA and the antenna 
by the low pass filter. But the bandpass filter should be taking care of 
that unless its bandswitch is in a wrong position, but then SSB and CW 
signals wouldn't get through.
Display not initializing to the band is a hint of bandswitch contact or 
soldering problems on the oscillator/mixer board.
Looks like the bandswitch shaft has to come out, then the osc-mixer 
board has half a dozen mounting screws.
Check all the boards for solid grounding, I've fixed many a radio 
locally and by remote control by tightening the mounting screws to get 
the board grounded again. And in some of those the transmitter would 
oscillate out of band. Screws could have shaken loose in shipping.
73, Jerry, K0CQ

On 2/22/2011 9:47 AM, Curt wrote:
> Thanks for the info.  Yes, the power switch is no big deal, can you
> elaborate further on the "switch pins" would this be on the 80711 Osc-Mixer
> board?  Did you remove it to do the soldering?  How?
>
> Further the high current problem.  On CW, everything seems to work fine and
> high current is not an issue.  On SSB, keying the mike produces 12 amp
> current draw, but no output power until microphone spoken into.    So,
> carrier balance doesn't seem to be the issue.  And, since CW doesn't exhibit
> high current I'll conclude PA isn't an issue.  I'm suspicious about C16 on
> 80718 SSB board, which is a 4.7M electrolytic
>
> ----- Original Message -----
> From: "Al Gulseth"<wb5jnc@centurytel.net>
> To:<tentec@contesting.com>
> Cc: "Curt"<rhulett1@consolidated.net>
> Sent: Tuesday, February 22, 2011 9:24 AM
> Subject: Re: [TenTec] Omni C Questions ( Maybe OT )
>
>
>
> On Tue February 22 2011 8:16:03 am Curt wrote:
> > Having bought an Omni C from a ham in NY who claimed it had no operating
> > issues, found my trust in fellow hams is sometimes misplaced.
> >
> > I have a few questions about the issues identified (so far):
> >
> > Power switch won't stay "on". My Omni D/B is push for "on", which matches
> > the manual's description for this Omni C, this one is pull for "on", but
> > will drop to "off" unless something isn't wedged between the switch knob
> > and panel. Did Ten Tec change the sense of the power switch with the Omni
> > C?
> The switch may have been changed out at some point in its life. They are a
> known trouble spot. The easiest way around it is to put a jumper across the
> switch contacts and use the switch on the PS.
>
> > Only one of the 10M positions ( 28.5) has a crystal. None of the WARC
> > positions has a crystal. My Omni D/B has all 10M positions filled, and 30M
> > functions on receive. More troublesome is that the band switch seems
> > "flaky", with the display changing to 1.0000, requiring rocking the switch
> > to restore normal frequency. Is this a known issue with these rigs?
> > From the www.qsl.net/tentec/specs/546c.jpg Omni C ad: "All 9 hf bands --
> only
> crystals are needed for the 18 and 24.5 MHz bands." I'd say that all of the
> 10M crystals should have been there from the factory as well as the 30M one.
> As to the band switch, rather than cleaning being needed, it could instead
> need resoldering on the crystal section. I went through that a few years
> back
> on a Corsair that would die after it had been operating for a while. (I'm
> guessing here that the physical architecture of the Omni C is very close to
> that of the Corsair in this case.) I called TT repair and they recommended
> checking the solder issue. Sure enough, there were hairline cracks around
> the
> _square_ switch pins of the crystal section which were in _round_ holes on
> the PC board. A quick "slurp" of the pins with the solder sucker followed by
> resoldering cured the problem and the Corsair was still going strong when a
> buddy of mine across town caught me in a weak moment and convinced me to
> swap
> it to him. (The "square [switch/pot/relay] peg in a round [PC board] hole"
> issue is not unique to TT - I've also dealt with it in older automobile
> electronics and test equipment to name just a few other places.)
>
> > Most troublesome, on SB-N, keying the microphone causes the indicated
> > current on the TT-255 to run up to about 12 amps constant, even though the
> > ALC isn't lit and regardless of ALC or drive setting. Talking will cause
> > the ALC to blink on voice peaks but the current rises until the TT-255
> > trips. ( The SWR is 1:1 ) Would this indicate that the carrier isn't being
> > suppressed, problem with the SSB Generator board? Anyone else had similar
> > experiences they successfully solved?
> it might be a carrier suppression issue, but it might be a PA bias issue.
> Or,
> (hopefully not) bad/shorted final(s)?
>
> 73 es GL with this one, Al
>
> > I bought this rig because wanted 30M capability and spare potential. Maybe
> > the rig has too many issues to meet those goals.
> >
> > 73, Curt KB5JO
> >
> >
> >
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