[TenTec] OMNI-C frequency unstable

Mon Aug 22 23:03:30 EDT 2005

RON, The next time it happens spray some non-inductive themo-cool spray on different caps,transistors, components..etc. I bought my last can at radio shack a few years ago. It comes with long small spray nozzle. I have found many problem areas using this technique. The extremely cold spray makes the bad part contract back together and start conducting again. Doesn't always work, but can eliminate some areas.  cul roger w4iv
---------- Original Message ----------------------------------
From: "Ron" <ron at morell.us>
Reply-To: Discussion of Ten-Tec Equipment <tentec at contesting.com>
Date:  Mon, 22 Aug 2005 09:34:56 -0700

>As a further report on this problem, the radio has been operating since this
>last report without a flaw, so last night I installed the top cover on the
>radio and within 30 minutes and shortly after a CW QSO the frequency became
>unstable and the hash box noise on the receiver.  I removed the top cover
>and poked around with my finger for something hot and not finding it, I
>turned the radio off for 5 minutes, turned it back on and it is functioning
>correctly again.  So my problem with this old Omni C seems to be related to
>the top cover and it would seem some heat related problem in an amplifier or
>oscillator.  Guess I'll just run the rig topless and see how it goes.  HI
>73
>Ron
>KA7U
>
>
>-----Original Message-----
>From: tentec-bounces at contesting.com
>[mailto:tentec-bounces at contesting.com]On Behalf Of Ron
>Sent: Sunday, August 14, 2005 8:19 AM
>To: Discussion of Ten-Tec Equipment
>Subject: Re: [TenTec] OMNI-C frequency unstable
>
>
>Thanks Mike for the good leads and the encouragement. I've been up late
>tonight working on her and put it back together and worked PSK31 with it for
>about 30 minutes and it behaved well.  Hmmm... now if I just knew what I did
>that actually solved it I'd tell you.  Any way, I sprayed all the POTS and
>unplugged and plugged in circuit boards, especially the VFO amp and the
>Oscillator boards.  Those have band switches and are harder to remove, but
>all for a good cause eh?  Also unplugged the crystals and stuff.  Checked
>out the diodes in the circuits and generally poked and prodded everything.
>Put the lids on and hooked it up and so far it is behaving nicely.  No noise
>on the receiver and the heat sinks are almost to hot to hold on to.  I just
>don't know what it is that caused the problem, but for now she is up and
>running like a new rig, so if it is working don't fix it, right?
>73 and thanks.
>Ron
>KA7U
>
>
>-----Original Message-----
>From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]On
>Behalf Of Mike Hyder -N4NT-
>Sent: Saturday, August 13, 2005 9:40 PM
>To: Discussion of Ten-Tec Equipment; ron at morell.us
>Subject: Re: [TenTec] OMNI-C frequency unstable
>
>Hi, Ron--
>
>The first thing to do with an Omni-C that has almost any trouble is to
>remove and reseat each printed circuit card (one at a time).  While each
>card is out of the rig, inspect it closely for bad solder joints or other
>obvious trouble.  Then if there is a molex connector with a jumper on the
>rear panel, remove the jumper plug and reinsert it.
>
>If the instability is only on one band, troubleshoot that band's oscillator.
>
>If the instability is on all bands then here are the things I would check in
>the order I'd check them:
>
>1.  There ought to be a potentiometer internal to the radio which sets the
>offset tuning.  This is to balance the control on the front panel.  A dirty
>potentiometer will create trouble for you.
>
>2.  The next thing is to put a frequency counter on the output of the BFO
>crystal oscillator.  This oscillator has detailed instructions in the manual
>about how to align the padder capacitors.  Another fellow suggested using
>DeOxit and I concur with him that the wipers of those padder capacitors
>ought to be treated with DeOxit.  If that BFO oscillator is unstable, you'll
>find it in this step.
>
>3.  About the last thing would be the PTO.  Remember that the PTO has a
>switching voltage applied to it which is used on 10 meters, I think, to move
>its frequency a bit to avoid birdies (at least this is the way the Tritons
>worked).  With your counter, you ought be able to see if the PTO is unstable
>in its frequency output.  If so, then you will want to monitor the different
>voltages applied to the PTO to see if one of them is causing your trouble.
>
>I'd appreciate your telling all of us what you find wrong with that rig.
>
>73, Mike N4NT
>
>----- Original Message -----
>From: "Ron" <ron at morell.us>
>To: "TenTecReflector" <tentec at contesting.com>
>Sent: Saturday, August 13, 2005 12:08 PM
>Subject: [TenTec] OMNI-C frequency unstable
>
>
>OK, I'm stumped.  My OMNI-C lost 4 diodes on the SWR/TR board a while back
>and I replaced them and the AGC circuit works again, but after some use on
>CW the receiver will start to drift up and down in frequency by 100 to 200
>cycles and then it will start to make noise in addition.  During transmit
>this produces a warbly chirp.  Turn the radio off for 10 minutes or so and
>it will start up and run fine for a while.  The power supply seems fine but
>I've tried another and the same effect is occasionally observed.  I have an
>OMNI D that does not seem to have a problem with either power supply.  If I
>connect and use the external VFO, the same problem can occur, so I do not
>believe the PTO needs rebuilt or any of that type of thing.  I'm fairly
>certain the problem is either voltage regulation or an oscillator that warms
>up and becomes unstable, hence the noise.
>
>So any suggestions of what to look for and where to look, in this old but
>beautiful OMNI C ?  I bought her new long ago and now I see it in the Ten
>Tec museum, and some call her vintage, but I hate to let this rig go down.
>Any suggestions of what could cause this anomaly will be appreciated.
>Ron
>KA7U
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