[TenTec] Logic Board, inquiring minds want to know

[Dr. Gerald N. Johnson]

On Mon, 2008-06-02 at 08:51 -0400, RLBrannigan wrote:
> I bought the radio, used, in Nov 1998 and had it checked out by Ten-Tec. All 
> OK. In August 1999 I had the display go out and sent the radio to 
> Sevierville. They said  "No problem found on display complaint" and 
> suggested a power supply problem. The Ten-Tec 961 and Pyramid 20A power 
> supplies each have sufficient voltage. In March 2001 I again returned the 
> radio for the same problem. It was returned "Unable to reproduce complaint."
> 
> This year I had the display go out again. After two trips, Paul finally 
> reproduced the display problem. His conclusion is that is the Logic Board 
> and they no longer stock the item. To do the detective work required to find 
> the problem, which I believe to be mechanical, i.e. bad solder joint, 
> defective cap etc. would take too many man hours and cost more than the 
> radio is worth.

So get out the temperature controlled soldering iron and the good solder
with an activated rosin flux and heat every solder joint on the whole
board. And if that doesn't work get out the hot air gun (a hair dryer
works) and the Freeze-mist, and cycle the board temperature from hot to
cold and back to see if that can recreate the fault and its cure, then
split the heated and cooled area into smaller portions until down to the
component level. Replace the bad component(s). Boards act like bad
solder connections, ICs can have bad bonds internally and act the same
way, but both are USUALLY affected by thermal cycling to give up their
location.

If the logic is TTL or at TTL compatible voltage levels, I have an HP
logic comparator that is handy for seeing if a chip is doing the logic
its supposed to do. That's handy too, was a couple hundred bucks new 205
years ago, ought to be far more affordable on the surplus market these
days and far handier than a logic probe or scope for checking out faulty
logic chips. Though with a logic data book in hand, logic can be traced
and checked that way. I've seen opens and I've seen gate inputs shorted
together in the chips which gives strange results, but when logic levels
are examined with a scope, such anomalies show up as not quite full
logic voltage level changes.
> 
> No the radio has not been abused. Even though I live in Florida, the 
> lightning capitol of the world, the antenna is physically disconnected when 
> I am not operating. Mains AC is supplied via Two (2) ganged surge 
> suppressors. Additionally, please check out Jim Bobo post of  8 August 2005 
> wherein he states the Logic Board no longer available. That was 2.5 years 
> ago. I suppose had Ten-Tec repair diagnosed the problem correctly in 1999, I 
> would still be in business, but hindsight is always perfect.
> 
> Further commentary available OFF THE BOARD at W2EJG at ARRL.net. Save the 
> negative comments, I already have enough of a headache.
> 
73, Jerry, K0CQ