Swann CUBIC ASTRO 102 BX Service Manual page 170

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SUBJECT: ASTRO-102BX EXCITER BOARD
Receiver audio on the ASTRO-102BX and ASTRO-102BXA Transcei vers has been reported
to be distorted on some units. This distortion, if noticed, may be èliminated
by the addition of a ground strap to the exciter board. Strap should be made of
a flat braided strap such as a coaxial cable shield braid (RG-58 type) or
equivalent type conductor. Use the braid only, not the whole cable. This modi-
fication note only applies to the original ASTRO-102BX configuration with the
2 pole CW narrow crystal filter with or without the 6 pole CW narrow crystal
filter -installed on an auxiliary circuit board. Later model circuit boards will
have provisions for the 6 pole filter on the exciter board and will have adequate
grounding installed at the factory.
INSTALLATION PROCEDURE
1. Remove the si x screws whi ch fasten the bottom cover and remove cover.
2. Locate the exciter board (the board in the center towards the rear of the
chassis).
3~ If the exciter board has not had the optional 6 pole CW narrow filter added
to the unit, salder the ground strap between the tops of transformers T104
and T105 and the top of crystal filter FL102. Refer to the attached layout
drawing for locations. Be careful not to overheat either the -transfarmers
or the filter case while soldering.
4. If the exciter board has had the optional 6 pole CW narrow filter installed
on the auxiliary board, salder one piece of the ground strap between the
tops of T104 and 105 and from the top of T105 to the top foil on the
auxiliary board near the filter. Salder a second piece of ground strap
between the top foil of the 6 pole CW narrow filter board near FL102 and
the top of FL 102. Be careful not to overheat either the trànsformers or
the filters while soldering.
5. Turn the transceiver power on and observe audio quality while listening
to a signal. Vary the PASSBAND tuning control while listening to noise.
If an increase in distortion or nulls or peaks in noise areobserved, the
effects are due to phase shift through the filter. In this'case, -try an
alternate position for the ground strap and repeat the observation until
satisfactory performance is obtained.
6. Replace the bottom cover .
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