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@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
>
>
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> TenTec@contesting.com
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