MAINTENANCE NOTICE
September, 1998 MN-98-007
DIGITAIR
®
SBU Model 6695, CDU Model 6696, EOT Repeater Model 6680
Transceiver Module Replacement
REASON FOR REPLACEMENT
US&S is now supplying a synthesized radio
transceiver module for the DIGITAIR
®
End-
of-Train product
line. This product line
includes the SBU Model 6695 End Unit,
CDU Model 6696 Front Unit, EOT HOTD
6680, and EOT Repeater Model 6680.
In the past, these models incorporated a
crystal-controlled transceiver (US&S P/N:
N24600004) which is no longer supplied by
US&S. These products are now shipped
with a new synthesized transceiver module
(US&S P/N: N24600007).
When equipment maintenance requires the
replacement of an existing crystal-controlled
transceiver module installed in one of these
products, a Synthesized Transceiver Kit can
be ordered from US&S under part number
X24600011
. This kit includes the following
parts:
1. Synthesized Transceiver Module
2. Metal Shim
3. New FCC/IC Certification Label
4. Quantity 2 Screws (6-32 X 1/2 Pan-Head)
REPLACEMENT PROCEDURE
The new synthesized transceiver module is
fully fit and function compatible with the
SBU Model 6695 End Unit. The metal shim
(item 2) and the screws (item 4) are
required when installing the new transceiver
into the CDU Model 6696, CIU HOTD 6680,
or EOT Repeater Model 6680.
This equipment contains static
sensitive components. Always
work at a grounded workstation
and observe proper ESD handling
practices, otherwise, equipment
damage may result.
Installation into the SBU Model 6695
1. Turn OFF power to the SBU by removing
its batteries.
2. Remove the existing crystal-controlled
transceiver from the SBU by following the
instructions in US&S Service Manual
6497 (aluminum case SBU) or SM 7066
(composite case SBU).
3. Replace with the new synthesized
transceiver module using the existing
fasteners.
4. Per the Service Manuals, adjust the
trimpots on the SBU processor board.
These are trimpot R62 to set RF transmit
power, R50 to set TX deviation, and R43
to set the RX audio level. Refer to the
Operational Test Charts in the manuals.
The new synthesized transceiver does
not require any adjustments for RF
transmitter or receiver center frequency,
however, the transmitter carrier should be
checked to ensure that it is within
specification (+/- 675 Hz). Ensure that
the trimpots are re-locked using Glyptol
(or equivalent) when the adjustments are
complete.
5. Reassemble the SBU as described in the
Service Manuals.
CAUTION
