PRODUCT IMPROVEMENT PROGRAM FOR REPLACING THE GENERATOR DIODES ON CERTAIN 795F AC OFF-HIGHWAY TRUCKS Caterpillar

PRODUCT IMPROVEMENT PROGRAM FOR REPLACING THE GENERATOR DIODES ON CERTAIN 795F AC OFF-HIGHWAY TRUCKS

Usage:

REBE7967-00

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31Jan2012

U-55

A-47

D-49

O-52

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*Priority*	PRODUCT IMPROVEMENT PROGRAM FOR REPLACING THE GENERATOR DIODES ON CERTAIN 795F AC OFF-HIGHWAY TRUCKS
4473		PI31986

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NOTE:

This Program must be administered as soon as possible. When reporting the repair, use "PI31986" as the Part Number and "7751" as the Group Number, "56" as the Warranty Claim Description Code and "T" as the SIMS Description code. Exception: If the repair is done after failure, use "PI31986" as the Part Number, "7751" as the Group Number, "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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COMPLETION DATE	TERMINATION DATE
31Jul2012	31Jan2013

PROBLEM

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The 123-3460 and 123-3461 Diodes need to be replaced on certain 795F AC Off-Highway Trucks. The existing diodes can fail, resulting in an open circuit, which can render the truck inoperable.

AFFECTED PRODUCT

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Model	Identification Number
795F AC	ERM00151-00191

PARTS NEEDED

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Qty	Part Number	Description
3	3857084	DIODE-STANDARD
3	3857097	DIODE-REVERSE
In order to allow equitable parts availability to all participating dealers, please limit your initial parts order to not exceed 40% 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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Remove the 123-3460 Standard Diodes and replace them with the new 385-7084 Standard Diodes. Remove the 123-3461 Reverse Diodes and replace them with the new 385-7097 Reverse Diodes.

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OWNER NOTIFICATION

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U.S. and Canadian owners will receive the attached Owner Notification.

SERVICE CLAIM ALLOWANCES

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Caterpillar		Dealer Suggested		Customer Suggested
Parts %	Labor Hrs%	Parts %	Labor Hrs%	Parts %	Labor Hrs%
100%	100%	0%	0%	0%	0%

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NOTE: This is a 6.0-hour job

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PARTS DISPOSITION

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

MAKE EVERY EFFORT TO COMPLETE THIS PROGRAM AS SOON AS POSSIBLE.

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COPY OF OWNER NOTIFICATION FOR U.S. AND CANADIAN OWNERS

XYZ Corporation
3240 Arrow Drive
Anywhere, YZ 99999

PRIORITY - PRODUCT IMPROVEMENT PROGRAM FOR REPLACING THE GENERATOR DIODES ON CERTAIN 795F AC OFF-HIGHWAY TRUCKS

MODELS INVOLVED - 795F AC OFF-HIGHWAY TRUCKS

Dear Caterpillar Product Owner:

The generator diodes need to be replaced with new, improved diodes on the products listed below. The existing diodes can fail and may render the truck inoperable. You will not be charged for the service performed.

Contact your local Caterpillar dealer immediately to schedule this service. The dealer will advise you of the time required to complete this service.

Please refer the dealer to their Service Letter dated 31Jan2012 when scheduling this service.

We regret the inconvenience this may cause you, but urge you to have this service performed as soon as possible to prevent unscheduled downtime.

Caterpillar Inc.

Identification #(s)

Attached to 31Jan2012 Service Letter

Rework Procedure

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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 front lower right-hand side of the Generator housing, remove the access cover for the Rotating Rectifier Assembly.

Image1.2.1

One of three connections points that are used to connect the positive lead of one diode, the negative lead of another diode and one exciter armature lug to the rotating plate.

(10) Red positive diode flying lead

(11) Diode base lead connection to the DC rotating plate

(12) Mechanical connection that passes through the insulated hole in the DC rotating plate (the insulation provides electrical isolation from the rotating plate)

(13) White sheathed exciter AC input lead

(14) Black negative diode flying lead

Image1.3.1

Detail view of the hardware that is used to connect a black/blue negative diode flying lead, a red positive diode flying lead, and the white sheathed exciter armature lug to the plate. Three of these connection points are located on the Rotating Rectifier Assembly.

(15) 1/4-20 inch nut

(16) Belleville washer

(17) Flat washer

(14) Black negative diode flying lead

(10) Red positive diode flying lead

(18) White sheathed exciter armature lug

(19) Flat washer

(20) Rotating plate

(21) Flat washer

(22) Belleville washer

(23) 6.4 mm (0.25 inch) x 31.8 mm (1.25 inch) hex head bolt

Image1.4.1

The positive lead of one diode and the negative lead of the other diode removed from the connecting bolt. The exciter armature lug, the connecting bolt, and the back side washers remain in place (arrow).

(10) Red positive diode flying lead

(14) Black/Blue negative diode flying lead

Image1.5.1

Torque Specs (See Illustration)

1/4-20 inch nut (15) ............. 8.1 +/- 1.4 N.m
(72.0 +/- 12.0 lb in)

3/8-24 inch nut (24) ............. 10.0 +/- 1.0 N.m
(88.5 +/- 8.9 lb in)

Follow this procedure in order to replace the diodes.

Note: Before proceeding with this procedure, mark the flying leads on the six new diodes. Mark the leads to separate the new diodes from the diodes that will be removed and replaced.

1. Use the barring tool to rotate the Rectifier to a point where one of the three diode flying lead connections to the rotating plate can be accessed. Remove the 1/4-20 inch locknut and the washers that are used to secure the two diode flying leads to the exciter armature plate.

2. Disconnect the blue/black negative lead of one diode and disconnect the red positive lead of the other diode from the connecting bolt. Do not remove the exciter armature lug, the hex head connecting bolt,or the back side washers from the rotating plate.

3. Use the barring tool to rotate the Rectifier to a point where the base lead of one of the diodes that has the flying lead disconnected can be accessed.

4. Remove the 3/8-24 inch nut and washer from the threaded diode base stud. Remove the diode from the mounting hole. Removal of the nut from the base stud will damage the threads on the diode stud. A new nut will be supplied with the new diode.

5. Place the base lead of a new diode in the hole on the DC plate. Carefully install the washer and the new nut on the base lead stud of the new diode. Tighten the new 3/8-24 inch nut according to the torque specifications that are listed at the start of this procedure.

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

6. Use the barring tool to rotate the Rectifier to a point where the base lead of the other of the diode that has the flying lead disconnected can be accessed.

7. Repeat step 4 and step 5.

8. Use the barring tool to rotate the Rectifier to the point where the disconnected flying leads for the two new diodes can be accessed.

9. Connect the flying leads of the two new diodes to the exciter armature plate connection. Install the hardware in the same original order. Tighten the 1/4-20 inch nut according to the torque specifications that are listed at the start of this
procedure. Do not overtighten the nut.

10. Use the barring tool to rotate the Rotating Rectifier Assembly to the point where another of the three diode flying lead connections can be accessed. Repeat these steps in order to change the two diodes.

11. 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 all of the diode leads 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.