PRODUCT SUPPORT PROGRAM FOR REPLACING GENERATOR DIODES ON CERTAIN 794 AC OFF-HIGHWAY TRUCKS Caterpillar

PRODUCT SUPPORT PROGRAM FOR REPLACING GENERATOR DIODES ON CERTAIN 794 AC OFF-HIGHWAY TRUCKS

Usage:

TEBE5748-00

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30Jan2017

U-54

A-35

D-42

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Before/After	PRODUCT SUPPORT PROGRAM FOR REPLACING GENERATOR DIODES ON CERTAIN 794 AC OFF-HIGHWAY TRUCKS
4450 4473		PS45369

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NOTE:

Caterpillar’s obligations under this Service Letter are subject to, and shall not apply in contravention of, the laws, rules, regulations, directives, ordinances, orders, or statutes of the United States, or of any other applicable jurisdiction, without recourse or liability with respect to Caterpillar.

NOTE:

This Program must be administered either before or after failure. In either case the decision whether to apply the Program is made by the dealer. When reporting the repair, use "PS45369" as the Part Number and "7755" as the Group Number. If administered before failure, use "56" as the Warranty Claim Description Code and "T" as the SIMS Description code. If administered after failure, use "96" as the Warranty Claim Description Code, and "Z" as the SIMS Description Code.

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NOTE:

The information supplied in this service letter may not be valid after the termination date of this program. Do not perform the work outlined in this Service Letter after the termination date without first contacting your Caterpillar product analyst.

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TERMINATION DATE

31Jan2019

PROBLEM

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The existing Generator Didoes can fail on certain 794 AC Off-Highway Trucks. If the existing Generator Diodes fail it will cause unplanned downtime.

AFFECTED PRODUCT

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Model	Identification Number
794 AC	MN500052-00056 MT500100-00101, 108-111

PARTS NEEDED

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Qty	Part Number	Description
3	2D6235	LOCKNUT
6	4N3884	WASHER-SPRING
3	5P2675	BOLT
6	7X0623	WASHER-HARD
9	8T4205	WASHER-HARD
6	2643617	LOCKWASHER
3	4889244	DIODE-STANDARD
3	4889245	DIODE-REVERSE
6	4889246	SLEEVE-DIODE
In order to allow equitable parts availability to all participating dealers, please limit your initial parts order to not exceed 32% of dealership population. This is an initial order recommendation only, and the ultimate responsibility for ordering the total number of parts needed to satisfy the program lies with the dealer.

ACTION REQUIRED

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Refer to the attached Rework Procedure and replace diodes proactively every 5000 hours.

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SERVICE CLAIM ALLOWANCES

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Product smu/age whichever comes first	Caterpillar		Dealer Suggested		Customer Suggested
Product smu/age whichever comes first	Parts %	Labor Hrs%	Parts %	Labor Hrs%	Parts %	Labor Hrs%
0-10000 hrs, 0-72 mo	100.0%	100.0%	0.0%	0.0%	0.0%	0.0%

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NOTE: This is a 6.0-hour job If there has been a previous repair, part age/hours will apply. Retain a copy of the previous repair invoice in the dealer's records for audit purposes, and specify repair date and machine hours in the "Additional Comments" section of the warranty claim.
Replace diodes proactively every 5000 hours.

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PARTS DISPOSITION

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Handle the parts in accordance with your Warranty Bulletin on warranty parts handling.

Rework Procedure

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Refer to the Service Manual if/as necessary.

NOTE: The 390-2031 and 390-2032 Diodes will no longer be used in 390-2000 Generators.

Before performing this procedure, the Power Train Electrical System Service Shutdown procedure must be performed to verify that the voltage in the system components is discharged.

Refer to the Troubleshooting, "Electrical Shutdown and Voltage Discharge" section of the manual in order to perform the Power Train Electrical System Service Shutdown procedure.

Before performing this procedure, ensure that the Engine Lockout Control is in the ON position (lock out) and the Battery Disconnect Switch is in the OFF position (battery negative disconnected). Lock and tag both of the disconnects.

Note: This procedure will require manual rotation of the truck engine in order to rotate the Generator Rotating Rectifier Assembly. A manual 279-3473 Barring Device tool or an air powered 329-3831 Barring Group tool should be used to rotate the Engine and the Rotating Rectifier Assembly during this procedure. Install the barring tool according to the installation and operating instructions that are provided with the tool.

Image1.1.1

At the bottom of the Generator housing at the non-drive end, remove the access cover for the Rotating Rectifier Assembly.

INSPECTION

Image1.2.1

Image1.2.2

1. Disconnect one of the two Main-Rotor (field) and Ring-Resistor connections (A) from the Rotating Rectifier. Separate the larger Main-Rotor (field) lug from the smaller Ring-Resistor ring terminal. Check the resistance of the Ring-Resistor (E). Connect one lead of the ohmmeter to Ring-Resistor ring terminal and the other lead to the second DC connection on the Rotating Rectifier. The resistance should be approximately 5 ohms.

2. If the resistance of the Ring-Resistor is far greater than 5 ohms or Open circuit, disconnect the other Main-Rotor (field) and Ring-Resistor connection from the Rotating-Rectifier. Separate the larger Main-Rotor (field) lug from the smaller Ring-Resistor ring terminal. Check the crimp of the ring terminals on the Ring-Resistor leads. Measure resistance of the Ring-Resistor again directly across the ring terminals. If the Ring-Resistor is greater than 5 Ohms, contact Caterpillar Product Support.

3. Check that the cord wrap (B) that secures the three Exciter Armature AC leads to the rotor is still in place. The lacing is required to prevent damage to the leads during operation.

Image1.3.1

One of three AC insulated connection points on Rotating-Rectifier DC plate.

(10) Standard diode positive flying lead

(11) Diode base connection to the DC rotating plate

(12) AC connection - Bolt passes through the insulated hole in the DC Rectifier plate

(13) White sheathed exciter AC lead

(14) Reverse diode negative flying lead

Image1.4.1

Detail view of the new hardware that is used to connect a Reverse diode negative flying lead, a Standard diode positive flying lead, and the white sheathed exciter armature lead to the plate. Three of these AC connection points are located on the Rotating Rectifier Assembly.

(15) Locknut 1/4-20 (2D-6235)

(16) Spring Washer (4N-3884)

(17) Flat Washer (8T-4205)

(14) Reverse Diode negative flying lead

(10) Standard Diode positive flying lead

(18) White sheathed exciter armature lead

(19) Flat Washer (8T-4205)

(20) Insulated hole in Rotating-Rectifier DC Plate

(21) Flat Washer (8T-4205)

(22) Spring Washer (4N-3884)

(23) Bolt 1/4"-20 (5P-2675)

Image1.5.1

Standard Diode - 488-9244 (Red Sleeve) replaces 390-2032 (Blue Sleeve)
Reverse Diode - 488-9245 (Black Sleeve) replaces 390-2031 (Red Sleeve)

NOTE: The 390-2031 and 390-2032 Diodes will no longer be used in 390-2000 Generators.

1. Install a threaded 488-9246 Sleeve on each of the new diodes. The sleeve must bottom out on the base of the diode as shown in Image 1.5.2. The purpose of the sleeve is to center the smaller studded diode in the oversized hole.

Image1.6.1

Image1.6.2

2. Rotate the Rectifier to access one of the three AC connection points. Remove all of the 5/16" hardware that secures the two diode flying leads and armature lead to the rectifier plate. The 5/16" hardware will be replaced with 1/4" hardware.

Image1.7.1

3. Rotate the Rectifier to access the base connection of one of the diodes that has the flying lead disconnected.

4. Remove the M12 nut and washer from the diode base stud. Remove the diode from the mounting hole. All hardware will be replaced.

5. Install one of the new diodes of the same polarity as the removed diode. Insure the sleeve is in place as the stud is inserted thru the hole in the Rectifier plate. Orient the diode base so that the flying lead connection can be made with minimal twist. Secure the base of the diode to the plate using a 7X-0623 Hard Washer, 264-3617 Lock Washer, and 5B-9079 Half Nut. Tighten to 13.5 +/- 1.0 N.m (120 +/- 9 in-lb).

Image1.8.1

CAUTION: The stud on the diode is plated copper - do not over-tighten the nut or the diode can be damaged.

6. Rotate the Rectifier to access the base connection of the other diode that has the flying lead disconnected.

7. Repeat steps 4 & 5 to install a new diode of the opposite polarity.

8. Rotate the Rectifier to access the flying lead AC connection point for the new diodes.

9. Install a new 1/4 inch 5P-2675 Bolt with a 4N-3884 Spring Washer and 8T-4205 Hard Washer thru the insulated hole in the Rectifier plate from the rear. Install a 8T-4205 Hard Washer on the bolt on the other side of the plate, under the Exciter Armature AC lead lug. Check that the bolt passes through the AC lead lug.

10. Install one of the diode flying lead lugs on the bolt, oriented so it lays flat against the Exciter Armature AC lead lug.

Image1.9.1

11. Install the flying lead lug of the other diode on the bolt, oriented so it lays flat against the first diode flying lead lug. Proper diode flying lead orientation is shown in image 1.9.1.

Image1.10.1

12. Install a 8T-4205 Hard Washer, 4N-3884 Spring Washer, and 2D-6235 Locknut. Tighten to 8+/-1 N.m (72+/-12 in-lb). Verify that all three lugs lay flat against each other.

13. Repeat these steps until all six of the original diodes have been replaced with the new diodes.
Once all six of the diodes have been replaced, verify that the diodes connected to each of the three AC connections are opposite polarity. Verify that all of the diode leads and bases are properly installed and tightened. Ensure that no tools, hardware, or other debris is present in the rotating diode assembly area before installing the access cover on the Generator.