Technical Support Document 015 - 2/96

REBUILDING A SENTINEL ENLARGER ENCODER MODULE

This document gives instruction on the rebuilding of a Sentinel Encoder Module. Disassembly of the module's mechanical items is covered, with a view towards replacing any of the mechanical components, particularly the thin steel measurement cable, that may fail. Replacement of the digital encoder itself is not covered, since it is a precision installation done at the factory.

Below is a cut-away view of the encoder drum module. Following are the procedures for replacing the following components:

• Steel Measurement Cable- Allows linear measurements by pulling it from the module
• Tensator Spring- Applies constant spring tension to the Measurement cable

Replacing the Measurement Cable:

Replacement of the measurement cable is done by first winding the Main Drum to develop spring tension, then fastening the end of the new cable to the drum and letting the cable spool back onto the drum.

1. Remove the encoder nodule from the Sentinel Enlarger, following the proper procedure for doing so.
2. If the module is a Lens Encoder Module, remove the two plastic covers on either side of the module body. This can be done by prying one of them off using a medium-sized flat-head screwdriver. The Second Plate may then be pushed off from the inside with the same screwdriver.

3. In the case of a column encoder module, note that the encoder cable drum is attached to a mounting bracket, and that an output bearing bracket is also attached. This bracket holds the output pulley that allows the cable to make a 90-degree turn as it exits the module. DO NOT DIS-ASSEMBLE THESE AT THIS TIME. Disassembly is not necessary to replace the cable or spring.
4. To replace the measurement cable, you will need to remove the old one. If the cable had broken and is wound up inside the module, you will probably have to cut it into several pieces to remove it entirely. Take whatever measures are necessary to remove all parts of the old cable.
5. Once all the old pieces of cable are removed, inspect the tensator spring and see if it will need replacing.
6. If the spring needs replacing, follow the instructions in the next section: Replacing the Tensator Spring.

7. Once the spring is replaced, or if it is not in need of replacement, we can install the new cable. Locate the proper cable for the particular unit that you are rebuilding: the Lens and Neg Stage drums use different cables. Refer to the diagram below to determine which cable to use.
   

8. If you are replacing a Lens Stage Encoder measurement cable, use one of the cable clamps provided in the kit, and clamp it onto one end of the cable. This end will then be the "Free" end of the cable.

9. Referring to the drawings above, locate the end of the cable noted as the "Cable Drum End." Thread this end of the cable into the exit hole of the encoder module. In the case of a neg encoder module, the cable's end must be inserted through both of the bushings, routing it around the bearing pulley to make a 90-degree turn.
   

10. Before attaching the new cable to the drum, you will need to wind the main drum to full spring take-up. Refer to the drawing at the beginning of this document for the proper direction of wind. The drum will usually take about 12-13 turns for full winding. Once the drum is wound, do not let go of it, since it will spin uncontrolled, and damage the spring. Use a strong adhesive tape to hold the drum ion place while working. Apply the tape on the flat area of the rum's surface, and secure the other end of the tape to the edge of the encoder module enclosure.
11. To attach the cable to the drum, locate the small hole that is located at one edge of the flat surface of the drum. This is where the cable attaches to the drum. See drawing below.

12. Insert the "Cable Drum" end of the cable into the hole indicated in the drawing at right. Push the cable through the hole so that 6" protrudes through the hole in the side of the drum. This may take some wriggling of the cable in order to get it through the hole on the side if the drum.
13. On the free end of the cable, tie a regular square knot (like a pretzel) about 1 inch from the end of the cable. Use one or two pairs of needle-nose pliers to make the knot very tight. The drawing below shows this situation.

14. Once the knot is tight, heat it with a regular cigarette lighter. This will prevent the knot from coming loose.
15. Gently pull the cable so that the knot is pulled into the hole in the side of the drum. The knot should be unable to be pulled through the small hole; it should hole the cable securely to the drum.
16. Next, grasp the free end of the cable, beyond the exit bushing of the encoder module and pull it to take up any slack along the entire length of the cable.

17. Firmly grasp the very end of the cable, taking up all slack, and then release the tape holding the wound drum in place. The cable will now have tension on it. Orient he module so that the exit bushing is straight with the travel of the cable, then slowly let the cable be pulled in by the tension of the spring until it is fully taken up. Again, do not let the exit bushing become skewed on the cable as the cable travels through it.
    
    

18. Once the cable is in place, pull it out to full extension and let it slowly retract. Hold the end at all times; do not let the cable retract uncontrolled, as this will destroy the cable and the tensator spring.
19. The encoder module is now ready for re-installation in the Sentinel enlarger.

Replacing the Tensator Spring:

Before starting this procedure, please follow the instructions for Replacing the Measurement Cable up to step #6.

1. Check o see that the old tensator spring is fully unwound and that the measurement cable is completely removed.
2. Locate the attachment screw which holds the spring onto the main cable drum. This screw should be visible when the spring is completely un-wound. Remove this screw. The spring should now be free of the main encoder drum.

3. To remove the spring from the smaller storage drum unwind it from the drum, curling up to form a new loop of free spring. See the figure below.
   

4. When you reach the end of the spring, you will se the brass core of the storage drum. The spring will now be in a small roll or coil, and completely free of the storage drum.
5. To install he new spring, locate the end of the spring and pull it around the storage drum core. Make sure that it is started in the right direction. Refer to the drawing below.

6. Once the end of the spring is started, continue winding the spring onto the storage drum until it's entire length is on the drum. Once this is done, the end of the spring that has a hole in it should be visible.
7. The next step is to attach the end of the spring to the main cable drum. Using the screw provided, fasten the end of the spring to the main drum, on the flat part of the spring's winding area. Make sure that the spring is attached such that it crosses over and forms part of a figure-eight. Refer to the drawing at the beginning of this document for a view of proper installation.
8. Once the spring is attached in this manner, proceed with step #7 of the Replacing the Measurement Cable section of this document.

If you have any questions or problems regarding this procedure, please contact the offices of ZBE, Inc., at the address and phone numbers in the info section or e-mail our service manager at support@zbe.com.