[TenTec] Delta Transmit Problems

[MadScientist]

The only boards with band sensitive components are the bandpass filter 8056, the low pass filter 80561 and the crystal oscillator board 80563. 

On 80561, the same tuned elements are shared between 12 meters and all 10 meter positions. Thus a single point failure on this board could not cause the three bands you observe to fail to fail.

On 80562, the same tuned elements are shared between all 10 meter positions. Thus a single point failure on this board could not cause the three bands you observe to fail to fail.


On 80563, none of the crystals are used on more than one band. However, for 160, 80 and 40 meters, Q2 is the crystal oscillator with Q3 operating as the buffer output stage. On all of the remaining bands, Q1 is the oscillator with Q3 operating as the buffer output stage.  Thus a single point failure on this board could not cause the three bands you observe to fail to fail either.

This leaves you with either multiple failure points (likely relays) or a common PC board trace that is shared by tuned elements only on 20, 17 and 12 meters. This is indeed a possibility since Ten Tec did what they could to optimize board space (as did all good manufacturers) but this sometimes required some rather odd signal trace paths. That, combined with often very thin traces could bring a multi band failure to the foreground.

In addition, severe contamination of band switch contacts can cause multiple band failures but these are usually less predictable in their appearances.

If you chose to clean the switches as a diagnostic, use care, quick and light applications because the plastic used in these switches is pretty solvent sensitive. What solvent you DO apply needs to be injected into the round holes of the rotors of the switches to do any good, especially if used lightly as I recommended.

If you have a scope, finding which point of signal loss is the issue should be fairly straightforward.

Gary 

W0DVN


> On Dec 30, 2018, at 2:51 PM, john marks via TenTec <tentec at contesting.com> wrote:
> 
> Old Delta will not transmit on on 20,17, or 12 meters, everything else is working fine. 
> Any ideas before I crack it open?
> JohnKM4CH
> 
> 
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec