Union Switch & Signal DIGITAIR 6695 Operation and maintenance manual

MN-99-006
645 Russell Street
Batesburg, SC 29006
MAINTENANCE NOTICE
DIGITAIR® End-of-Train Telemetry
SBU Model 6695 End Unit
Solid-State Motion Detector Modification
(P/N: N24610101)
July, 1999
© 1999, Union Switch & Signal Inc.
Printed in USA
UNION SWITCH & SIGNAL
An Ansaldo Signal Company

MAINTENANCE NOTICE
July, 1999 MN-99-006
DIGITAIR® SBU Model 6695 End Unit
Solid-State Motion Detector Modification
Equipment Affected
This Maintenance Notice applies to SBUs
equipped with BOTH of the hardware items listed
below, or SBUs receiving either of these items
as replacement spare parts:
1. A Solid-State Motion Detector (MD), US&S
p/n: N24610101 as shown in Figure 1, and;
2. A Pressure Transducer date coded in 1998
(e.g., G0198-046, H0798-038)
or later
as
shown in Figure 2.
SBUs with Pressure Transducers date coded
prior to 1998 should not be affected.
Figure 1 – Solid-State Motion Detector
Figure 2 – Transducers (showing date code)
Reason for Modification
US&S has learned that the manufacturer of the
Pressure Transducer implemented a design
change in 1998 that causes an increase in the
startup current when the transducer is powered-
on. The SBU routinely turns the transducer on
and off to conserve battery capacity. The
increased transducer startup current causes a
transient on the power line feeding the Solid-
State Motion Detector’s processor chip which in
turn may cause it to output false motion status.
The problem is clearly visible when observing the
motion indicators on an EOT Front End Unit
such as the CDU Model 6696. With air pressure
applied to the SBU while it is standing still, the
CDU motion indicators will typically cycle from
STOPPED to MOVING (while also showing
either FORWARD or REVERSE), and then back
to STOPPED.
Corrective Action
The problem is corrected by reducing the
transient level as seen by the MD’s processor.
This involves soldering a surface mount
technology (SMT) diode and capacitor to the
backside of the MD board as shown in Figure 3.
The diode and capacitor are available from
US&S as listed below:
1. SMT Schottky Diode (P/N: J726102-0015).
2. SMT Cap, 22uF, 20V (P/N: J709153-0024).
Figure 3 – Parts Soldered to Back of MD Board
Capacitor
Diode

MAINTENANCE NOTICE
July, 1999 MN-99-006
Installation Procedure
Prior to performing the installation procedure,
observe the following:
The SBU contains static sensitive
components. Prior to removing the SBU’s
Rear Panel, or while working on the internal
electronics, always follow proper ESD
handling practices, otherwise equipment
damage may result.
The Solid-State Motion Detector Board is
manufactured using Surface Mount
Technology (SMT) components. Only
technicians experienced in SMT rework
should attempt to perform this modification.
1. Remove the SBU’s Rear Panel.
2. Confirm that the SBU is equipped with a
Solid-State Motion Detector and a Pressure
Transducer as stated in the “Equipment
Affected” section. If the date code on the
transducer is not easily visible, use a small
mirror to check it.
3. Remove the Motion Detector Assembly from
the Electronics Cage by unplugging the ribbon
cable from the Processor Board and
unscrewing the two mounting bracket screws.
Set the screws, flat washers, and lock-
washers aside for reinstallation later.
4. Use an appropriate scraping tool (i.e., a
Single Sided Razor Blade or Exacto Knife) to
remove the conformal coating and solder
mask in the areas identified in Figure 4.
5. Cut the trace as shown in Figure 4.
6. Tin the scraped copper traces with solder.
Figure 4 – Areas to be Scraped & Cut
7. Hand solder the SMT diode and capacitor as
shown in Figure 5.
Figure 5 – SMT Components Soldered to Board
CAUTION
NOTE
Scrape & Cut
Trace Here
Scrape Trace
Here Scrape Ground
Plane Here
Cut Trace Here
CLOSE UP
Diode Cathode Stripe
This Side
Capacitor

MAINTENANCE NOTICE
July, 1999 MN-99-006
8. When soldering the diode, ensure that its
cathode (marked with a white line) is oriented
as shown.
9. When soldering the capacitor, ensure that
the positive side (marked with a line) is
oriented as shown. Also take care not to
short the plus side of the capacitor to the
ground plane.
10. Clean excess flux from reworked area and
touch up conformal coating, if possible.
11. Reinstall the Motion Detector using the
screws and washers that were set aside in
Step 3. When plugging the Ribbon Cable
back into the Processor Board (J5), ensure
that the Red wire is facing upwards towards
Pin 1.
12. Reinstall the SBU’s Rear Panel.
End of Procedure
Technical questions or information regarding the
contents of this Maintenance Notice should be
directed to the
R.A.I.L. Team via telephone at
1-800-652-7276 or via Internet e-mail at:
[e-mail].