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TM-9-1200-215-34&P Technical Manual for M109 Automatic Fire Control System (AFCS) Download

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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.