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HP Scitex FB500 Industrial/FB700 Printer - Resolving Error Code E-MM-52 "Invalid Belt Encoder Ratio Calculated"

Environment
HP Scitex FB500 Industrial Printer
HP Scitex FB700 Printer
Control Panel
Media Drive System
Questions/Symptoms
E-MM-52 Invalid belt encoder ratio calculated
Cause
Dirty high-resolution encoder hub
Media drive motor encoder cable connection
Answer/Solution
The media drive system of the FB500 and FB700 printers uses a pair of encoders to control motion of the media belt. A standard-resolution encoder on the media drive motor measures motor velocity; a high-resolution encoder on the drive roller itself measures movement and position. When the belt is in motion, the printer software compares the feedback from these two encoders. If the feedback from the two encoders produces a result that is outside of what is acceptable, the software displays the message E-MM-52 Invalid belt encoder ratio calculated.

Feedback from the encoders may be disrupted by an accumulation of foreign debris on the high-resolution encoder, or by a poor cable connection to the motor encoder. The remainder of this support article describes how to address each of these possible causes of the error.
To access the encoders, the endcap enclosures of the printer must be removed. Figures 1 and 2 describe the orientation of the printer and the location of the endcap fasteners.

Figure 1 Printer orientation vocabulary
Input Side - where media is loaded
Output Side - where completed prints exit
User End - where the control panel is located
Service End - where the service station is located


Figure 2 Location of fasteners for the user-end and service-end endcap enclosures
1 - Fasteners for the service endcap (9 locations)
2 - Fasteners for the user endcap (9 locations)
PWR - Location of the printer power switch (shown for orientation)

Using a #2 Phillips screwdriver, remove all fasteners from all locations shown in Figure 2 and set them aside. To fully remove each endcap from the printer, lift the endcap up and then pull away from the printer. Each endcap will remain attached to the printer by cables, but there is enough slack to move the endcaps out of the way for the rest of the procedure. Ensure that the cables do not create a tripping hazard.

Follow the remaining steps below to address the possible causes of the error.

Reseat the media drive motor encoder cable
1. Remove the service endcap as described above.
2. Power off the printer.
3. Locate the media drive motor, found at the service end of the main drive roller for the media belt, which is located on the output side of the printer.
4. The encoder is located at the outermost end of the drive motor. See Figure 3.


Figure 3 - Media drive motor encoder and encoder cable
1 - Encoder
2 - Encoder cable connection

5. With the printer powered off, disconnect the encoder cable fully from the motor encoder. Inspect the connectors to verify there is no other issue, then carefully reconnect the cable to the encoder, ensuring that it is fully seated.
6. Power on the printer and observe to see if the error has been corrected and no longer appears on the control panel.
7. If the error does not appear, the endcap(s) may be reattached to the printer and normal operation resumed.
8. If the error does appear, continue to the next section below.

Clean the high-resolution encoder hub
To clean the high-resolution encoder hub, end users will need one or both of the following:
- canned compressed air
- a long-handled (approximately 10 cm or 4") cleaning swab. For cleaning the hub, HP recommends using HP service tool CQ114-67181 SERV_TOOL,RENISHAW_RING,CLEANER,U. If CQ114-67181 cannot be obtained, use a long-handled cleaning swab moistened with 99% denatured ethyl alcohol.

NOTE: Part numbers can change without notice, please verify the part numbers from HP PartSurfer website. Click here to view HP PartSurfer website.

1. Remove the user-end endcap as described above.
2. Leave the printer powered on.
3. Locate the user end of the media drive roller, found at the output side of the printer. The end of the roller is covered by an additional metal enclosure, which must be removed to gain access to the high-resolution encoder hub. See Figure 4.

Figure 4: Fasteners for the output side, user-end belt enclosure. Note that in this Figure the user endcap is shown as installed; this endcap will already have been removed in the present procedure.
1 - Belt enclosure fasteners (3 locations)

With the belt enclosure removed, the end of the main drive roller with the high-resolution encoder hub will be exposed. The hub is a precision-etched ring attached to the flat end of the drive roller. Figure 5 identifies the encoder hub itself.

Figure 5: The high-resolution encoder hub. In this illustration, many components have been removed to allow clarity of viewing and identification. It is not possible in real life to expose the hub fully as shown in this figure. See Figure 6, below, for the real-life appearance of the hub area.
1 - High-resolution encoder hub. The red-colored band, visible in this illustration only on the left area of the teal-colored hub, is the etched encoder surface that requires cleaning

4. Using canned compressed air, blow out the area of the encoder hub to dislodge any accumulated dust, media particles, or other foreign debris that might have contaminated the hub.
5. If the printer is currently displaying the E-MM-52 error, press the Retry button. The printer will again attempt to move the drive roller and get feedback from the encoders. If the compressed air has removed the contaminants that were causing the error, the error will clear.

End users may be able to press the Retry button multiple times until the software gives up and continues with initialization. Initialization may complete, but if the problem has not been corrected, the printer will still show error messages when end users attempt to move the belt using the buttons on the control panel. If the error condition persists after using compressed air, continue to the next steps.

6. Using the long-handled swab described above, clean the encoder hub as shown in Figure 6. Have an assistant press the control panel buttons to nudge the roller forward to allow access to the entire hub for cleaning.

Figure 6: Cleaning the high-resolution encoder hub. Note well the surface that is actually being cleaned.
1 - Encoder hub surface being cleaned

7. Continue cleaning until the entire circumference of the hub has been cleaned.
8. When complete, shut down the printer using the main power switch. Wait for two full minutes, and then turn the printer on again. Allow the printer to initialize and observe to see if the error has been resolved.
9. If the error does not appear, reinstall the belt enclosure and reattach the endcap(s) to the printer, and normal printer operation may be resumed.
10. If the error does appear, repeat the cleaning and verify that the motor encoder cable (described above) is still connected securely.

If the error persists after performing these procedures, contact an authorized HP reseller or contact the regional HP Customer Care Center for further assistance.

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