785G Off-Highway Truck Systems Caterpillar

Illustration 1	g01944888
Interface module fiber optic connector (disconnected)

Illustration 2	g01944435
Phase module low voltage connector and the mating harness connector (1) Alignment posts that are used to aid in the alignment of the connectors. The posts are not used for electrical connection. (2) Four fiber optic circuits in the upper half of the connector body (3) Four copper wire low voltage power supply and temperature sensor circuits in the lower half of the connector body

For specific connections to each phase module, refer to the complete machine electrical schematics.

At the interface modules, each fiber optic circuit is individually connected using single fiber optic connectors.

At the phase module connector, the fiber optic circuits are terminated in a round 28 contact connector. The connector also contains the low voltage power and temperature sensor circuits.

The interface module converts the voltage signal to a light pulse that is sent to the phase module through single plastic fiber optic conductors. A diagnostic feedback light pulse is sent back through a separate fiber optic feedback circuit to the interface module. The interface module converts this feedback light pulse to a low voltage signal that is sent back to the specified ECM through a copper wire circuit. This feedback signal allows the ECM to monitor the transistors for correct operation.

Fiber optic circuits are used for the following reasons:

• Electrical Isolation

The use of the fiber optic driver and feedback circuits insures that an internal short circuit that could allow a high-voltage circuit to come into contact with a low voltage circuit cannot occur

• High-Speed Operation

Fiber optic circuits are easily capable of handling the high speed switching signals.

• Resistance to Electronic Interference

Fiber optic circuits are not as susceptible to the electromagnetic interference that can be created during the high-voltage switching operation.

Connection, Disconnection, Cleaning, and Routing of the Fiber Optic Circuits and Connectors

The fiber optic circuits and connectors require special handling to ensure proper operation. Mishandling of the circuits or connectors can result in either poor circuit operation or a complete failure of the circuit.

The fiber optic circuits and the fiber optic connectors are not serviceable.

If a fiber optic harness circuit or a fiber optic harness connector is damaged or has failed, the complete harness for the involved phase module will have to be replaced.

If a fiber optic connector on an interface module or on a phase module is damaged, the interface module or the phase module that has the damaged connector will have to be replaced.

Disconnecting and Connecting the Fiber Optic Connectors

In general, do not disconnect or handle the fiber optic connectors unless a problem is suspected or you are instructed to disconnect the connectors while performing a service procedure. Minimal handling of the fiber optic connectors will help to prevent the potential for damage or contamination.

When a disconnect is necessary for a fiber optic connector, the following guidelines should be followed:

Note: Do not use excessive force when disconnecting or reconnecting the fiber optic connectors. Do not use any type of tool to disconnect or reconnect the fiber optic connectors to the interface modules or to the phase modules. The use of hand tools on the connectors will cause damage the fiber optic circuit connectors.

Connect or disconnect the fiber optic connectors using hand pressure only. These connectors should never require more than a small amount of force to be used for disconnection or reconnection. Do not force the connection of the fiber optic connectors. If a greater amount of force is required for disconnection or connection, there is a problem that could result in replacement of either the wiring harness, an interface module, or a phase module.

Disconnecting an Interface Module Fiber Optic Connector

Illustration 3	g01944948
Disconnecting an interface module fiber optic connector

1. Place your thumb and forefinger on the grooved retaining collar. Exert gentle pressure to push the collar straight inward against the spring force.

2. Once the collar is pushed in, rotate the collar counterclockwise to the stop. Pull the connector straight out to clear the retaining posts and the female connector.

3. Do not touch the exposed end of the optical conductor. Position the connector a clean dry surface. If work is performed in the area of the disconnected fiber optic connector, protect the connector from damage or contamination.

Connecting an Interface Module Fiber Optic Connector

Illustration 4	g01945071
Interface module fiber optic circuit connection assignments

Illustration 5	g01944432
Interface module fiber optic circuit connection

1. Do not touch the exposed end of the optical conductor. Verify that the exposed end of the fiber optic cable is clean and in good condition.

2. Line up the alignment tab on the single fiber optic connector with the alignment slot on the interface module connector. The interface module driver circuit connectors have the alignment slot facing upward. The interface module feedback circuit connectors have the alignment slot facing downward.

3. With your thumb and forefinger on the grooved retaining collar, rotate the collar to the position where the slots line up with the retaining posts. Exert gentle pressure to push the collar straight inward against the spring force and turn the collar clockwise to lock the connector in place.

4. When released, the collar and the connector should remain in place in the interface module connector.

Disconnecting a Phase Module Low Voltage Connector

Illustration 6	g01944952
Disconnecting a phase module low voltage connector that contains fiber optic circuits

Note: To loosen the connector retaining collar from the phase module connector, a full hand grip may be required to move the retaining collar from the detent position. Do not use hand tools on the connector. A positive pressure in the counterclockwise direction will be sufficient to loosen the collar.

1. Use one hand to steady the wiring harness in place. Place your thumb and forefinger or a hand grip on the grooved retaining collar. Rotate the collar in the counterclockwise direction to overcome the detent position.

2. Rotate the collar counterclockwise until the connector can be pulled straight out. Carefully pull the connector straight out and away from the mating phase module connector.

3. Do not touch the exposed ends of the optical conductors. Position the connector a clean dry surface. If work is performed in the area of the disconnected fiber optic connector, protect the connector from damage or contamination.

Note: Once a fiber optic connector has been disconnected, inspect the exposed ends of the fiber optic cable for damage or contamination. Clean the ends of fiber optic cables using the process that is presented in the "Cleaning Fiber Optic Connectors" section that follows this section.

Connecting a Phase Module Low Voltage Connector

Mishandling of the low voltage harness connector for the phase module during the connection process can cause the fiber optic cables to be pushed back into the harness connector body or the mating phase module connector body. This condition will cause the circuits to be inoperable. This condition is not repairable. This condition requires replacement of either the complete wiring harness or replacement of the phase module.

The following procedure provides instruction on the correct steps to follow when connecting the low voltage harness connector to the phase module.

Illustration 7	g01945142
The low voltage and fiber optic phase module connector (top) and the mating harness connector (4) The top mounted alignment tab and alignment slot.

For specific fiber optic circuit connections to each of the drive motor phase modules, refer to the "System Schematics" pages in the back of this manual.

Illustration 8	g01945181
Connecting the low voltage and fiber optic harness connector to the phase module connector

1. Do not touch the exposed end of the optical conductors on the connectors. Verify that the exposed ends of the fiber optic cables and the power circuit contacts are clean and in good condition.

   Note: In the next step, when the harness connector is in the alignment position and is moved into the mating connector, no resistance to the inward movement should be encountered. If any resistance is felt while moving the harness connector into the mating connector, the connector is not properly aligned. Carefully pull the connector back and start the process over. Ensure that the harness connector is in the correct alignment position before the inward movement is initiated.

2. To align the tab with the slot on the mating connector, use both hands to hold the harness in a vertical position. Move the harness connector in and lightly contact with the phase module mating connector. While holding the harness vertical and maintaining light contact with the mating connector, rotate the grooved outer shell to line up the alignment tab with the slot. Move the harness into a position where the alignment tab on the harness connector can be aligned with the alignment slot on the phase module connector. Once the alignment tab is in the proper position, carefully move the harness connector straight into the mating connector while rotating the collar clockwise to a position where the collar slots line up with the retaining posts.

3. While holding the harness connector steady in the straight alignment position, continue to rotate grooved collar clockwise. Apply slight inward pressure as the rotation of the locking collar pulls the harness connector straight into the mating connector. Rotate the locking collar clockwise until you feel the collar move into the locked detent position.

4. When released, the collar and the connector should remain securely in place in the phase module connector.

Cleaning Fiber Optic Connectors

Dust, dirt, or other forms of contamination that are present on the connector ends of a fiber optic cable can decrease the light transferring ability of the optical conductor. In extreme cases, intermittent problems or possibly a failure of the circuit can result.

Maintain the Inverter Cabinet Clean Air System

The Cabinet Pressurization Filter is in place to allow cooling air to circulate through the Inverter Cabinet. The filter will keep dirty or contaminated air out of the cabinet. Check and replace the cabinet pressurization filter at the recommended interval or sooner if required.

The cabinet compartment cover seals are designed to maintain the positive air pressure in the Inverter Cabinet and keep outside contaminates from entering the cabinet. When a cabinet compartment cover is removed for service or maintenance, ensure that the sealing material is intact and in good condition. Replace any worn or damaged seals. When a compartment cover is installed back on the cabinet, ensure that all the cover bolts are properly installed and tightened against the seals.

Contamination of the fiber optic cable ends should not be a common problem in the Inverter Cabinet when the compartment cover seals and the air pressurization filter system are properly maintained. However, the following cleaning procedure should be followed if a problem with a fiber optic circuit is suspected or when a fiber optic conductor is determined need cleaning.

Cleaning Supplies Commonly Used for Fiber Optic Cables

• A 10X magnification device - used to inspect the fiber optic conductor ends for contamination and cleanliness.

• Aerosol can of Clean Dry Air (CDA) - must be free of dust, water, or other contaminants. Do not use compressed air from an air hose.

• A 1.25 mm (0.05 in.) Fiber Optic Sleeve Cleaning Swab - A long thin foam tip swab that enables cleaning of the fiber optic camera lenses. The swabs can also be used to clean the conventional connector contacts. Do not use cotton swabs that can leave fiber residue on the optic ends.

• 90 percent or greater Isopropyl alcohol - do not use any other type of solvents or cleaning chemicals.

Fiber Optic Connector Cleaning Procedure

During the cleaning procedure and anytime that the fiber optic connectors are handled, do not touch the exposed end of the optical conductors.

1. Use the 10X magnification device to inspect the exposed fiber optic ends for contamination. At 10X magnification, the optical conductor end should be free of visible dirt, fibers, or any other forms of contamination. If cleaning is required, continue to the next step.
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   Illustration 9	g01945228
   Using an aerosol can of CDA to blow off a typical fiber optic connector

2. Use the CDA and lightly blow on the exposed end of the fiber optic cable to remove larger particles and loose debris.
   Show/hide table

   Illustration 10	g01945259
   Using the fiber optic sleeve cleaning swab moistened with isopropyl alcohol to clean the fiber optic harness connector for the interface module.

3. For the interface module connectors, wet the cleaning tip of the cleaning swab with a small amount of isopropyl alcohol. Use the cleaning swab to clean the fiber optic harness connector and the mating interface module connector. After cleaning each optical conductor end, immediately use a clean, dry cleaning swab to dry the surface to avoid leaving any residue. Use the magnification device to inspect exposed fiber optic ends for cleanliness.
   Show/hide table

   Illustration 11	g01947600
   Using the fiber optic sleeve cleaning swab moistened with isopropyl alcohol to clean the fiber optic connectors for the interface module.

4. For the phase module connectors, wet the cleaning tip of the fiber optic sleeve cleaning swab with a small amount of isopropyl alcohol. Insert the cleaning swab into the recessed fiber optic terminal on the harness connector to clean the fiber optic ends. Use the cleaning swab to clean the fiber optic ends on the phase module connector. After cleaning each optical conductor end, immediately use a clean, dry cleaning swab to dry the surface to avoid leaving any residue. The cleaning swabs can also be used to clean the conventional connector contacts.

5. Reconnect the fiber optic connector using the procedures that are outlined in the previous section. If the connector will not be reconnected for some time, protect the connector to prevent any type of contamination.

Routing the Harness in the Inverter Cabinet

The fiber optic circuits and the fiber optic connectors that are used in the truck electric drive train system are not serviceable.

If a fiber optic harness circuit or a fiber optic harness connector has failed, the complete wiring harness for the involved phase module will have to be replaced.

When a new wiring harness that contains fiber optic circuits must be replaced, special handling of the harness is required to avoid damage to the plastic fiber optic circuits.

The following guidelines must be practiced:

• Do not bend a new harness to an inside radius of less than 51.0 mm (2.0 in.). If the harness was formed into a circle, the minimum inside diameter of the circle that is formed by the harness should not be less than 102.0 mm (4.0 in.). Bending the fiber optic circuits at too small of a radius can damage the circuits.

• When a new wiring harness is received, each of the fiber optic connectors should have a protective cover installed. Individually remove the protective cover and verify that the exposed end of the fiber optic cable is clean, dry, and in good condition. Clean the cable if necessary using the cleaning methods in the previous section. If any type of damage is observed on any of the fiber optic connectors or other circuit contacts, exchange the wiring harness for another new harness.

• Before routing the harness through the cabinet, ensure that the protective covers are in place for each connector. Keep the covers in place as the harness is routed through the cabinet.

• As the harness is routed through the cabinet, do not pull on the harness or force the harness around a corner. Always support the harness and use two hands to feed the harness though openings or around obstacles.

• Rout the harness along the same path that the former harness used. Remember to keep the minimum bend radius of the harness at 51.0 mm (2.0 in.) or greater.

• Securely fasten the harness in place. Avoid overtightening the fasteners to prevent the cables from being crimped. Leave a length of the harness free at each end. The extra length of harness will avoid stress on the cables when the connection is made.

• Connect the connectors at the modules according to the methods that are presented in the previous section.