[TenTec] Omni C question

[Dr. Gerald N. Johnson]

On 5/10/2010 9:16 PM, Jeramy Ross wrote:
> I'd like to thank everyone for their replies.  Loads of good
> information, ranging from there will be minimal issues to there are
> some parts that will fail and you need to start stocking up on those
> parts now.  Quite a range!  A few trends seem to have emerged when
> combining this with posts in the list archive and various sources on
> the net.
>
> 1)  If you operate this rig conservatively, then everything should
> hold up quite well over time, and you should have a great rig that
> will probably out last the majority of people on this list.  If you
> operate this rig like a DX crazed contester, slamming the switches and
> spinning the knobs like a wildman in a DX induced fit of madness,
> things will wear out, break, etc.  The same goes for abusing the rig
> in any way.  (this pretty much goes without saying for any rig out
> there)
>
> 2)  There are some problem areas that seem to pop up with a bit of frequency:
>
>       A)  The Resonate control (RX preselector) seems to become loose
> and "wobbly" with time and use.  I am unsure of the mechanism of wear
> here as the fixes are as varied as the symptoms mentioned.  From
> fitting with felt washers, to actually going in and "rebuilding" the
> control (which unfortunately there were no details in this "rebuild"
> with that post on the internet so that didn't shed any light on
> things.
>
>       B) Obvious risks of PA damage from either not using a ps designed
> to work with this rig or not using an alternative protection device
> (fast acting circuit breaker or other current limiting circuit).  All
> examples of PA failure I have drug up from the depths of the internet
> involved failure that would, it seems, have been prevented had the
> operator had one of the aforementioned protection mechanisms in place.
>   Also, the PA transistors and drivers are still available, and for
> reasonable prices from many vendors and Ten-Tec themselves.

All the more reason to have some on hand because such parts tend to not 
be made anymore and so to go out of stock.
>
>       C) Bandswitch components are getting hard to find, and with
> abuse, can become loose, worn, and inoperable with time.  A parts rig
> or two with good bandswitch components should mitigate this failure
> for a very long time.  Also, again, this seems to be an area where the
> type of use was directly proportional with the failure rate.  Ten-Tec
> themselves mentioned that wear in this area of the radio was mainly
> seen in rigs that were "used hard."  Being a former Kenwood Hybrid man
> (collected, restored, repaired, and sold them), the bandswitch in
> those rigs (except for the section in the PA cage) seemed to be of a
> more delicate design and had issues of a different sort (dissimilar
> metal junctions that caused a nearly guaranteed corrosion issue at
> some point in the rigs lifetime and a weak shaft coupler design in the
> later rigs of that series... both easily fixed).  Even with those
> issues in mind, I had never seen nor heard of a worn out bandswitch in
> those rigs (other than from blatant abuse and ignorance when trying to
> work on one).  With that in mind, and those being contemporaries of
> each other, I am not worried about the bandswitch all that much.  I am
> assuming one will see similar lifetime and performance.  Also, have
> not seen any examples of this being a failure mode of these radios
> anywhere on the net, which seems to back up this assumption.
>
>       D)  Display controller chip.  Obsolete and long out of
> production.  However, it, and compatible variants were used in other
> rigs (both Ten-Tec and those of other manufacturers.  Yaesu FT-902DM
> (and 101ZD in later production models) used a similar IC with similar
> issues, and identical lack of availability.  A gentleman in JA land
> was able to produce a replacement with a programmable PIC and a
> handful of parts that assembled on a nice and neat daughter card that
> went into a socket that was put in place of the original chip.  It
> shouldn't be much harder to do the same for the Omni-C.  Even so,
> again, this is a mentioned point of failure, but little mention of
> actual failures in this area out there on the net.  Potentially a
> problem in the future, but not likely on any given rig.  Most mentions
> of failure also came with mentions of over/under voltage conditions or
> some other form of PS issue.  I believe there to be a relationship
> there.

Power supply issues as in dried out electrolytic bypass capacitors near 
the controller chip. A worse problem with a rig that hasn't been used in 
a long time, and keeping electrolytics on hand without using them is 
poor economy. When replacing the original its a good idea to go for the 
lowest ESR and highest temperature rated available from Mouser to get 
better life and performance. Some of the cheapest miniature 
electrolytics won't pass my power factor tests fresh out of the sack.
>
>       So, armed with that knowledge, I believe I have put most of my
> fears at rest, and am satisfied with my rig choice and fully expect it
> to last as long as I do with little issue.  The only area I still have
> questions is the resonate control wear.  It seems to be the most
> common issue.  What is the mechanism of the wear?  Is it merly a issue
> of things getting loose with use and out of adjustment?  Actual part
> wear?  Combination of the two?  What is the best fix?  I'm not a fan
> of the fiber washer fix so often mentioned as it seems like more of a
> band aid if there is an actual way to repair the cause of the problem
> (i.e. adjustment, mechanical parts replacement or refurbishment,
> etc.).  Thoughts, advice, knowledge happily accepted!
>
> Thanks again,
> Jeramy / W5XTL
> _______________________________________________
>
73, Jerry, K0CQ