[TenTec] Corsair - blank LED segments

[Dr. Gerald N. Johnson]

Fortunately for fixing but unfortunately for needing fixing, TenTec 
cables have been a weak part of the radios for a long time and still are 
in Orion I and II.

Best I can figure from the manual (which neglects to show the 
interconnects between the display boards) everything on the 68705 board 
is working in binary coded decimal And most of the counting is in a 
string of 74LS390 decade counter chips. Then the 74LS257s act as adders 
or multiplexors, I've not dug out the data further. Then that board with 
two BCD to 7 segment drivers and some logic buffers is where the data is 
converted to 7 segment to drive the segments.

Replacing the 68705 is one of those things we hope never has to happen 
because its custom programmed and TenTec doesn't want to remember the 
code for making more. But we know it goes awry when the electrolytics on 
that board get bad. Probably more true on the decoder/driver board.

A quarter drp of DeoxIT should help keep connections working longer 
between repairs.

Glad to know it fixed. My HP signal generator has starting showing 
similar symptoms since I moved it 25 miles.

73, Jerry, K0CQ

On 4/6/2011 4:55 PM, Barry N1EU wrote:
> On Wed, Apr 6, 2011 at 9:43 PM, Dr. Gerald N. Johnson
> <geraldj at weather.net>  wrote:
>> I expect a bad cable connection rather than a bad IC or
>> resistor.
>>
>
> Wallah.  Good advice.  On a scope, the segment driver line looked
> good.  So I fiddled the cable from the 68075 coming in (probably not
> the problem) and fiddled the board connectors that sandwich the
> driver/display boards together (probably the problem) and all the bad
> segments are back in operation.
>
> Still seems strange that the same segment went out on both the Mhz and
> Khz halves and no other segments were affected.  Glad to be able to
> fix it and glad Ten-Tec made such a serviceable radio!
>
> 73, Barry N1EU
> _______________________________________________
>