HP Scitex FB500/FB700 Printers - Cleaning the Carriage Encoder Reader Sensor

HP Scitex FB500

HP Scitex FB700

Carriage encoder reader

Carriage encoder strip

A-PR-1 incorrect number of carriage encoder pulses

E-HM-51 Carriage encoder error

Clean the carriage encoder sensor

Carriage Motion Failure

Dirty encoder reader

Cleaning of the carriage encoder strip is documented in the printer User Guide, chapter 9. Cleaning of the encoder reader sensor, however, is not documented. When cleaning of the encoder strip alone fails to resolve related printer issues, the next step is to clean the encoder reader sensor.

Locating and identifying the Encoder Reader sensor:
The encoder reader sensor (hereafter, simply "encoder reader") is located on the back side of the carriage assembly at the service-end, or "left" end, when facing the front of the carriage. Because of its location it is not easily visible. Figures 1 and 2 identify and locate the encoder reader.

Figure 1:

Figure 1 Service end of carriage assembly, viewed from the service end of the printer
1 – General location of the encoder reader. The arrow points to the two screws that retain the encoder reader bracket.

Figure 2:

Figure 2 Encoder reader location detail
1 – Phillips-head fasteners (black, qty. 2)
2 – Bracket (silver metal)
3 – Encoder reader sensor (black plastic)

Figures 1 and 2 establish the actual appearance and relative location of the reader. Figures 3 and 4 are drawings that show the reader in more detail but removed from the printer context.

Figure 3:


Figure 3 Drawing of encoder reader and strip. Some printer components have been removed for clarity.
1 – Encoder reader
2 – Encoder strip

Figure 4:


Figure 4 Drawing of the back side of the carriage. This view is not possible without completely removing the carriage from the rail, which is not required for cleaning the strip.
1 – Encoder reader
2 – Phillips-head fasteners for encoder reader bracket (shown for reference only)

Figure 5 shows the encoder reader and bracket assembly entirely removed from the printer. This is not required for cleaning, but is shown here to highlight that the sensor gap is only 1.7 mm (0.067 inches).

Figure 5:




Figure 5 Encoder reader assembly. Removed from printer only for clarity; it is not necessary to remove the sensor for cleaning.
1 – Sensor gap = 1.7 mm (0.067 in)

Do not attempt to clean the sensor with any implement that is significantly larger than 1.7 mm (0.067 in). Forcing a thicker object into the reader may damage the reader, thus requiring replacement.

CAUTION: Removing the sensor assembly is not recommended. If the sensor is removed, it requires correct realignment upon reinstallation to ensure that the reader does not scratch the encoder strip.


Cleaning the Encoder Reader:

Recommended method:
The easiest and most effective way to clean the encoder reader is to use a long-handled, flat-tip polyester swab moistened with 50% isopropyl alcohol (IPA). Such swabs are available from vendors of cleanroom supplies or from other sources. A flat tip approximately 2 mm thick is optimal; if only thicker swabs can be found, ensure that the tip easily compresses to safely fit the gap of the sensor, as shown in figure 5. To clean the reader using such a swab, follow the instructions below.

1. Power Off the printer. Ensure that the auxiliary power supply for the ink delivery system (IDS) vacuum is connected to the printer and energized.
2. Open the main output door and move the carriage by hand to the center of the rail.
3. Moisten a flat-tip swab with 50% IPA solution and insert it into the reader gap. Clean both the upper and lower areas of the reader. Note that when cleaning the lower part of the reader, the swab will most likely come in contact with the bottom side of the encoder strip. Use only 50% IPA, as a stronger solution may damage the encoder strip.
4. When cleaning with the moistened swab is complete, insert a dry swab and buff the same encoder reader surfaces dry.
5. Repeat steps 3 and 4 until the moistened swab comes out clean. Note that if the printer currently is or has previously been configured for white ink, white residue may not be easily visible on the swab.
6. Move the carriage back to the service end of the rail, close the output door, and turn the printer back on.

Alternate method
If long-handled, flat-tip polyester swabs are unavailable, the encoder reader may be cleaned by an alternate method. In this method, a strip of lint-free cloth is placed on the upper surface of the encoder strip and held in place with low-tack removable adhesive tape. The cloth strip is moistened with 50% IPA solution and the carriage is moved by hand so that the encoder reader passes over the strip and is cleaned by contact. The procedure is repeated with a cloth strip taped to the bottom side of the encoder strip to clean the other part of the reader. Ensure that the tape selected to hold the cloth will not leave behind any residue on the strip, and ensure that the IPA solution is 50%, or the bottom side of the strip may be damaged. When complete, ensure all foreign objects are removed before powering on the printer.

Troubleshooting
Any time the encoder reader is manipulated, there is a possibility that the reader will come off of the strip. If this occurs, the printer will be unable to print and will post error messages or Actions describing encoder strip or carriage motion problems. Check to see if the reader is off the strip. Figure 6 shows how the strip should pass through the reader.

Figure 6:




Figure 6 Detail of encoder strip passing through the reader
1 – Encoder strip
2 – Encoder reader
3 – Rail
4 – Carriage

To reinsert the strip into the reader, lift up slightly on the front of the carriage so that the carriage is pivoting from the top wheels. From the service end of the carriage, insert a long, smooth (no sharp edges) implement of some kind underneath the encoder strip to lift the strip slightly; then gently lower the carriage back into place. See Figure 7:

Figure 7:


Figure 7 Using an implement to lift the encoder strip.

NOTE: The model shown is not an FB500 or FB700, but the principle and procedure is the same. Some printer components have been removed in this photo for clarity.


Cleaning Swab resources:

The table that follows lists some possible products that may be suitable for cleaning the encoder reader.

NOTE: These items are suggestions only and have not been tested or qualified by HP. Use at your own discretion.

NOTE: One or more of the links above will take you outside the Hewlett-Packard Web site, HP does not control and is not responsible for information outside of the HP Web site.