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  • Information
    Information regarding recent vulnerabilities

    HP is aware of the recent vulnerabilities commonly referred to as "Spectre" and "Meltdown". HP has published a security bulletin with patches for these issues and a list of impacted systems. We will continue to update the bulletin as more information becomes available and encourage customers to check the bulletin frequently.

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HP Scitex FB500, and FB700 Printers - Resolving an'A-PR-1 Incorrect Number of Carriage Encoder Pulses' Error Message

This document is for the HP Scitex FB500 and FB700 printers.
This document explains how to resolve the 'A-PR-1 Incorrect Number of Carriage Encoder Pulses' error message and other carriage motion related issues.
The 'A-PR-1 Incorrect Number of Carriage Encoder Pulses' message appears on the control panel when the physical movement of the carriage (location and speed) becomes out-of-sync with the data being sent to the printheads for printing. The causes of the A-PR-1 message and other carriage motion-related errors or message can be grouped into three general areas:
  • Carriage encoder strip and/or carriage encoder reader issues
  • Mechanical or electrical carriage drive hardware problems
  • External interference with data
  note:
The A-PR-1 message often is seen in conjunction with the message E-CN-10 Action item occurred; operation canceled. The A-PR-1 Action, however, is not the only possible cause of the E-CN-10 message, and before undertaking the rest of this document it should be confirmed that A-PR-1 is the true cause of the E-CN-10 message. See HP support article Error Message E-CN-10 "Action item Occurred; Operation Canceled" for complete information on the E-CN-10 message itself.
Carriage encoder strip and/or carriage encoder reader issues
The carriage encoder strip is the clear or lightly gray-colored plastic strip that runs the width of the rail. It is found just above the blue main carriage drive belt.
    Figure : Encoder strip
    Image: Encoder strip
  1. Encoder strip
  2. Main carriage belt
On close inspection the strip can be seen to have an emulsion printing of many fine black lines.
    Figure : Two versions of encoder strips. Both are acceptable.
    Image: Close up of two encoder strips
  1. Older style
  2. Newer style
On the back of the carriage there is an optical sensor that straddles the strip. This sensor is the encoder reader.
    Figure : Encoder reader
    Image: Encoder reader
  1. Bracket attachment screws
  2. Bracket
  3. Encoder reader sensor
As the carriage moves across the encoder strip, the lines on the strip break the beam of the encoder sensor. The printer software and electronics count the number of lines read by the sensor to know the position and speed of the carriage while it is in motion. The data from the strip/reader interaction is referred to as “encoder pulses”.
The printer software expects to receive a certain number of encoder pulses in a specific interval of time when the carriage is in motion. If the software receives a different number than what is expected, it will cancel the current operation (such as printing an image) and show the message A-PR-1 Incorrect number of carriage encoder pulses. An incorrect number of pulses may be received for any of the following reasons related to the encoder strip itself or the carriage encoder reader:
  • Encoder strip is dirty.
  • Encoder strip is damaged.
  • Encoder reader is dirty.
  • Encoder reader is poorly positioned over the strip.
To resolve these possible problems, take the following actions:
  1. Clean the encoder strip. As noted above, the strip is a plastic base with a printed emulsion on one side. When properly installed, the emulsion is on the bottom of the strip. The top of the strip can be cleaned with a 50% solution of isopropyl alcohol (IPA) or a locally-approved substitute; check local regulations. The bottom of the strip with the emulsion may also be cleaned, but must be cleaned gently with no strong solvents or hard physical rubbing, as either of these can remove the emulsion and render the strip useless and requiring replacement. Refer to the HP Scitex FB500 Printer & HP Scitex FB700 Printer User Guide, Chapter 9, “User Cleaning” for instructions for cleaning the encoder strip.
  2. Visually inspect the encoder strip from end to end, including the sections inside the endcaps, such as where the carriage normally parks while idle and the opposite end behind the control panel area. Damage to the strip will typically cause the A-PR-1 or other carriage motion errors to occur when the carriage is at the damaged location. The Carriage Motion Troubleshooter found in the control panel menus, which is described in detail later in this document, can be used to identify specific problem locations on the strip.
  3. Clean the encoder reader using the instructions found in HP support article Cleaning the Carriage Encoder Reader Sensor.
  4. The encoder reader should be placed approximately centered over the strip, so that it does not rub on either the top or the bottom. The sensor gap is only 1.7 mm (0.067 in), so there is not a wide range of placement.
  5. Use the Carriage Motion Troubleshooter found in the control panel menus, which is described in detail later in this document, to test for normal function of the encoder strip/reader system.
Mechanical or electrical carriage drive hardware problems
A problem with the mechanical motion of the carriage will produce an incorrect number of encoder pulses, causing the A-PR-1 error to be displayed on the control panel.
Use the Carriage Motion Troubleshooter to diagnose carriage motion problems that may cause the A-PR-1 message. Use the results from each individual test to find any applicable corrective actions in the Carriage motion Troubleshooter results table.
  1. On the printer's control panel, go to System, then Tools, then User Diagnostics, and then Carriage Motion.
  2. Press Yes to run the troubleshooter.
  3. Run the Electrical Test. This test is a short test of connectivity to the electrical components. In the event that something does not pass, restart the printer and run the test at least two more times to confirm the failure. Many reported electrical failures are false failures that will not repeat.
  4. If all components passed, press Proceed to continue.
  5. Run the Position Test. This test requires an assistant.
    1. One person moves the carriage slowly by hand, the second person observes the number on the control panel.
      The control panel shows a number that represents the count of encoder pulses being detected by the encoder reader. The number should increase/decrease steadily in direct relation to the carriage movement. If there is a dirty or defective area of the encoder strip, the number on the control panel will stop changing, make a big skip, or some other atypical behavior every time the carriage passes over that area of the strip.
    2. Take note of any location where atypical behavior happens and clean the encoder strip in that area.
    3. Evaluate the carriage trolley bearings, the carriage should move freely by hand across the rail.
  6. The control panel will ask to run the Service End Position Test. This test requires an assistant. Select Yes and run this test.
    1. Follow the on-screen directions and take note of the beginning Position value shown.
    2. Move the carriage by hand all the way to the opposite end of the rail and then back again to the original position.
    3. Take note of the new Position value shown. This result should be +/- 50 from one iteration of the test to another.
  7. The control panel will ask to run the User End Position Test. This test requires an assistant. Select Yes and run this test.
    1. Follow the on-screen directions and take note of the beginning Position value shown.
        note:
      The value with the carriage at the user end of the rail should be 150 or less, but should not be a negative number. If the value is negative, return the carriage to the service end, exit the test, and start over, ensuring that the carriage is fully against the service end at the start of this test.
    2. Move the carriage by hand all the way to the opposite end of the rail and then back again to the original position.
    3. Take note of the new Position value shown. The results should be +/- 50 from one test to another.
  8. The control panel will ask to run the Slow Speed Motion Test. Select Yes and run this test.
    1. This test moves the carriage across the rail at a slow speed. Observe the carriage to see if it stops or has any other inconsistent motion.
    2. If the carriage does stop, take note of the location, then move the carriage by hand another 30 cm (12") in the same direction that it had been traveling. On the control panel, press Back, then press Yes to run the slow speed test run again.
      • If it starts up again and is OK until it comes back to that same spot, then there may be a problem with the encoder strip at that specific location.
      • If it starts up again but stops at another location, repeat the same procedure of moving the carriage by hand and then resuming the test.
        • If the motion fails at many locations with no discernable pattern, it may indicate a failing carriage drive motor. Continue to the next test for confirmation.
        • If the motion fails mainly when the carriage is at one or both ends of the rail where it changes direction, it may indicate a problem with slippage between the drive shaft and the main belt. Continue with the next test for confirmation.
  9. The control panel will ask to run the Full Speed Motion Test. Select Yes and run this test.
    1. This test moves the carriage across the rail at full printing speed. Observe the carriage to see if it stops or has any other inconsistent motion.
    2. If the carriage does stop, take note of the location, then move the carriage by hand another 30 cm (12") in the same direction that it had been traveling. On the control panel, press Back, then press Yes to run the full speed test run again.
      • If it starts up again and is OK until it comes back to that same spot, then there may be a problem with the encoder strip at that specific location.
    3. If the motion fails when the carriage is at one or both ends of the rail where it changes direction, it indicates a problem with slippage between the drive shaft and the main belt.
  10. Exit the Carriage Motion Troubleshooter.
  11. Take corrective actions appropriate to the test results, then repeat the tests.
    Results from the carriage motion troubleshooter and corrective actions.
    Test
    Result
    Meaning
    Action to Resolve
    Position test
    Numbers stop or jump suddenly at specific location(s)
    Dirty, worn, or defective encoder strip
    Clean both top and bottom surfaces of the strip. Replace strip.
    Position test
    Numbers change erratically through the entire length of the rail
    Dirty, worn, defective, or malpositioned encoder reader
    Clean encoder reader and verify position relative to strip. Replace encoder reader.
    Service End Position test or User End Position test
    Position value at service end is significantly different after moving carriage to user end and back again
    Dirty, worn, or defective encoder strip or encoder reader
    Clean both top and bottom surfaces of the strip. Clean encoder reader. Replace strip. Replace reader.
    User End Position test
    Position value at user end is a negative number
    Invalid test procedure, repeat test. If result continues under correct test procedure, dirty, worn, or defective encoder strip or encoder reader
    Clean both top and bottom surfaces of the strip. Clean encoder reader. Replace strip. Replace reader.
    Slow speed test
    Carriage stops at one or more specific locations every time
    Encoder strip problem at those locations
    Clean both top and bottom surfaces of the strip. Replace strip.
    Slow speed test
    Carriage stops mainly at the ends of the rail when turning around
    Main belt slippage
    Check and adjust main belt tension. Check drive shaft gritted pulley for wear. Clean contact side of belt. Replace drive shaft. Replace belt.
    Slow speed test
    Carriage stops erratically at many locations with no obvious repetition
    Loose main belt or worn drive motor
    Check main belt tension. Replace drive motor.
    Fast speed test
    Carriage stops at one or more locations every time
    Encoder strip problem at those locations
    Clean both top and bottom surfaces of the strip. Replace strip.
    Fast speed test
    Carriage does not stop but there is unusual noise when carriage turns around
    Main belt slippage
    Adjust main belt tension. Check drive shaft gritted pulley for wear. Clean contact side of belt. Replace drive shaft. Replace belt.
    Occasionally all of the carriage motion troubleshooter tests will pass with no problems, but print jobs continue to cancel with A-PR-1. Assuming that the external data interference issue has been ruled out satisfactorily, in these cases the encoder strip may require replacement anyway.
    If there are any questions or further assistance is needed, contact an authorized HP reseller or the regional HP Customer Care Center.
To resolve problems with the carriage drive hardware, use the following steps.
  1. Inspect the timing belt for missing teeth and replace it if missing teeth are observed.
  2. Inspect the carriage drive shaft. The drive shaft transfers the motion of the drive motor to the main blue belt through friction between a gritted pulley on the shaft and the contact surface of the belt.
      Figure : Carriage drive assembly
      Image: Carriage drive assembly
    1. Gritted pulley
    2. Toothed pulley
    3. Main carriage belt
    4. Toothed carriage timing belt
    If the gritted pulley has worn down and is now smooth, it will be less effective at transferring the motor power to the belt, and so the belt will slip or otherwise fail to impel the carriage normally. In some cases one of the pulleys on the shaft can move out of position, also creating abnormal motion. The Carriage Motion Troubleshooter can be used to test for slippage between the drive shaft and main drive belt.
  3. Inspect the main carriage belt tension. Tension is set by the idler assembly located on the service end of the rail.
      Figure : Adjustable idler design
      Image: Adjustable idler design
    1. The white plastic tip of the idler fork tongue
    2. Tab on the spring-retention bracket
    3. Gap at the top and bottom of the spring-retention plate
    In the adjustable idler design, the tip of the idler fork tongue should be even with the end of the tab on the spring-retention plate. The sides of the spring-retention plate should be the same distance from the tensioning bracket at the top and bottom, making the spring-retention bracket parallel with the tensioning bracket. If the tip of the fork tongue is not even with the tab on the spring-retention plate, then the belt is too loose and will create slippage, resulting in A-PR-1 messages.
      Figure : Non-adjustable idler design
      Image: Non-adjustable idler design
    1. Idler fork tongue
    2. Bracket
    In the non-adjustable idler design, the tip of the idler fork tongue should be even with the edge of the black bracket. If the tip of the fork tongue is not even with the bracket, then the belt is too loose and will create slippage, resulting in A-PR-1 messages.
  4. Inspect the main carriage drive belt for signs of wear. As noted above, the drive shaft transfers its motion to the main belt by friction. If the contact surface of the belt is worn smooth or has a buildup of foreign material on it, it will slip or otherwise fail to be moved normally. The Carriage Motion Troubleshooter can be used to test for slippage between the drive shaft and main drive belt. The belt can be reconditioned by cleaning any deposits using IPA or a locally-approved substitute, and smooth areas can be roughened by using fine-grit sandpaper, emery cloth, or a green Scotch-Brite scouring pad.
    If the main belt cannot be successfully reconditioned and a replacement belt is not available, the existing belt can be detached from the carriage and flipped over, so that the original contact surface is now on the outside and the previously unused surface is now making contact with the drive shaft. This procedure is outside the scope of this document and should be undertaken only by persons qualified to perform service on the printer.
  5. With the printer powered off, move the carriage by hand across the rail and observe for rough rolling, hesitation, or noise that could indicate a problem with one or more of the trolley wheels or wheel bearings. Ensure that the trolley wheels and the corresponding rail surfaces are cleaned and properly lubricated before drawing conclusions about the trolley wheels or bearings. See the printer’s User Guide for cleaning instructions.
    A failing drive motor may create unusual resistance that makes the carriage hard to move by hand, particularly in only one direction or the other. To eliminate or confirm the trolley bearings vs. the drive motor, detension the timing belt between the motor and the drive shaft so that the motor no longer is turned by the belt, then try moving the carriage by hand again. If the carriage moves freely with the motor no longer in the loop, the problem may be in the motor rather than in the trolley bearings or wheels.
External interference with data
Data from the carriage encoder system is sent from the carriage down to the printer electronics over a cable, and the print information is sent up to the carriage from the electronics the same way. Certain outside events can cause a disruption of this data transfer, which may result in the A-PR-1 message. These external events include:
  • Electrostatic Discharge (ESD) from media to the carriage during printing. Synthetic media, including but not limited to fluted polypropylene, PVC, polystyrene, acrylic, and films, can hold a static electrical charge. If this charge is not dissipated before the media passes through the print zone, it may discharge into the carriage as the carriage passes over the media. This ESD event may disrupt the data, causing the A-PR-1 message.
  • Interference from a malfunctioning printer component. The printer includes an anti-static ionizer bar mounted on the input side of the rail. In some cases, this ionizer bar or its power supply can malfunction and emit unusually high levels of radio-frequency (RF) interference. This interference can disrupt the data, causing the A-PR-1 message.
  1. Test print multiple jobs with a non-synthetic media, such as paper or cardstock. If the incidence of the A-PR-1 declines or disappears with these media, switch back to the synthetic media and observe if the problem returns. If so, there is evidence that the media is the source of the problem. Refer to HP support article Rigid Media Guide for a discussion of static mitigation techniques.
  2. Temporarily unplug the ionizer power supply (see figure 7) from the printer’s electronics, then test print. If the incidence of the A-PR-1 declines or disappears with the ionizer power supply unplugged, it is evidence that the ionizer system is malfunctioning and requires service or replacement.
      Figure : Example of the ionizer power supply
      Image: Ionized power supply
    1. Ionizer power supply, located near the carriage drive assembly on the user end of the rail. Follow the power cord from the power supply down to the electronics assembly and unplug it from the receptacle.
    Figure : Example of the power supply
    Image: Power supply
Related HP Spare Parts
The following table lists spare parts associated with the various issues and resolutions described in this document. Part numbers can change without notice, please verify the part numbers from HP PartSurfer website.
Part Number
Part Name
Part Description
CQ114-67162
FRM,CAR_ENCODR/BRKT,U
Main carriage drive encoder reader sensor with integrated cable, includes mounting bracket and associated hardware.
CH971-91425
FRM,RLD_E_STRP&FM,ABCDHIJ
Encoder strip and foam tape kit. It is long enough for a 98"/2.5m printer and can be trimmed down for smaller printers. This kit requires you to reuse the existing aluminum bar from the old strip.
CQ114-67110
FRM,ASSY,CARR_DRV_SHFT,U
Carriage drive shaft assembly, includes both pulleys and bearings.
CH971-90710
FRM,BLT,CARRDRV_TIMNG,MXABCDHIJ
Toothed carriage drive timing belt between the carriage drive motor and the carriage drive shaft.
CQ114-67219
SERV_TOOL,CARR_DRV_TIMING_BELT, TENSN
Reusable spacing tool to help set the correct tension on the carriage drive timing belt.
CQ114-67109
FRM,ASSY,CARR_DRV,U
Complete carriage drive assembly. Includes bracket, motor, drive shaft, timing belt, and all related fasteners.
CQ114-67022
FRM,FB500,CARR_BELT/CLIP,ASSY
Main carriage belt (blue belt) for FB500. Includes the metal clips that attach to the belt and secure the belt to the carriage.
CQ115-67052
FRM,FB700,CAR_BELT/CLIP,ASSY,SIZED
Main carriage belt (blue belt) for FB700. Includes the metal clips that attach to the belt and secure the belt to the carriage.
CQ114-67225
FRM,CARR_IDLR,ADV,U
Idler assembly for the main carriage drive belt. This version has the tension-adjust mechanism.

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