TM-9-1200-215-34-P
AUTOMATIC FIRE CONTROL SYSTEM (AFCS)
TECHNICAL MANUAL; DIRECT SUPPORT AND GENERAL SUPPORT MAINTENANCE MANUAL
FEBRUARY 1999
TM-9-1200-215-34-P - Page 141 of 266
TM 9–1200–215–34&P
5–3
Section
IV – MANUAL TROUBLESHOOTING
Page
Page
General
5–3
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Functional Description
5–3
. . . . . . . . . . . . . . . . . . . . .
Manual Troubleshooting Procedures
5–4
. . . . . . . . .
Post Maintenance Test
5–5
. . . . . . . . . . . . . . . . . . . . .
5–8.
GENERAL
This chapter contains information on checks and corrective actions required to isolate defects in the VMS
Modem, and correct the defects by means of maintenance.
The manual troubleshooting shall begin with a fault
or symptom and lead to a single fault isolation of the problem.
In cases where the maintenance must be
performed at a higher level, the description will note “Forward VMS Modem to Depot”.
5–9.
FUNCTIONAL DESCRIPTION
a.
There are two identical VMS Modem assemblies in the AFCS.
The list VMS Modem encodes and modulates the
odometer outputs of the VMS unit into unique frequencies.
These frequencies are transmitted over the slip rings to the
second VMS Modem.
The second VMS Modem decodes the frequencies to their original state for use by the AFCS
and vehicle navigation system components.
Also, the second VMS Modem will encode and modulate the BIT
commands into unique frequencies to be transmitted over the slip rings and decoded by the first VMS Modem.
The
second VMS Modem is additionally controlled by the BIT command and test outputs of the ACU.
VMS
MODEM #2
NAVIGATION
DEVICE
VMS
MODEM #1
VMS
DISPLAY
UNIT
– AFCS COMPONENTS
– NOT PART OF AFCS
SLIP
RINGS
ACU
Figure 5–1.
VMS Modem Block Diagram
b.
The VMS consists of:
D
VMS Modem Circuit Card Assembly
D
VMS Modem Heatsink Assembly Circuit Card
D
Cable Assembly
D
J1 Connector
D
J2 Connector
(1)
The VMS Modem CCA receives frequency lock detect inputs from the transmitting VMS Modem and
generates odometer, bit command, and loopback outputs of various pulse widths.
The time conditioner circuitry
shown in the figure delays the recognition of the lock detect input, filtering out false lock indications from the
transmitting VMS Modem.
The operational interface between the VMS Modem CCA and the AFCS is provided
by the J1 connector.
The J2 connector provides the test interface for the VMS Modem CCA.
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