Technical Support Document 019 - 4/97

REPLACING THE SENTINEL NEGATIVE STAGE ENCODER

The Sentinel Enlarger utilizes two measurements to accomplish it's autofocus functionality. These measurements are made through the use of two Encoder Modules, one located near the lens turret area and the other inside the body of the Negative Stage. This document outlines the replacement of the Negative Stage encoder.

The negative stage encoder uses a thin steel cable drawn from it's body under spring tension to detect its measurement. The encoder transforms mechanical movement of the cable into a series of electrical pulses that the Sentinel AF Computer can then decipher and use.

Important: When working with the Encoder Module, be vary careful at all times not to kink the cable while handling the unit. Any damage to the cable will result in inaccurate function, or no function at all, of the module. Never let the cable "snap" back into the unit if it is pulled by hand.

The steps for replacing the cable are as follows. The procedure is in four parts: Removing the Neg Stage Access Panel, Removing the Negative Stage Encoder Module, Installing the New Module, and Replacing the Cover.

REMOVING THE NEGATIVE STAGE ACCESS PANEL

1. Unplug the Sentinel enlarger. By hand, gently move the stages so that they are about 12 inches (30cm) apart and that the under side of the Negative Stage is in good view.
2. Remove the small screw that holds the top of the "Zig-Zag" Cable Guide Wire to the underside of the Neg Stage Access Plate. Let the wire pull on the Zig-Zag cable temporarily.
3. Remove all 17 of the screws holding the Access plate to the underside of the Negative Stage.
4. Once the plate is free, lower it just enough to gain access to the gray clip that holds the top portion of the Zig-Zag cable to the interior (upper) side of the access Plate. Undo the clip by pulling up on the notched end.
5. With the cable free of the Access Plate, slide the plate down on the cable until it rests on the top of the rear portion of the lens stage.

You may also wish to remove the Autofocus Computer box for easier access to the interior of the Negative Stage.

REMOVING THE NEGATIVE STAGE ENCODER MODULE

1. Remove the Neg Stage Encoder's measurement wire where it is attached at the top of the column. The end of the wire is terminated in a ring that is held in place by a small screw. Remove the screw while holding onto the wire to keep it from freely winding into the negative stage. Take care not to drop the screw into the top of the column. Keeping hold on the end of the wire, spool the wire back down into the Negative Stage as far as it will go.
   
2. With the Access Plate removed, the interior of the Negative Stage should now be accessible. Locate the Neg Stage Encoder Module centered at the rear of the compartment. The following figure identifies the various parts in this area.
   

1. From a round black plastic drum mounted to the side of the Encoder Module, you will see the encoder's electrical cable. The other end of this cable plugs onto the Junction Circuit Board mounted to the upper interior surface inside this compartment. Disconnect this cable's plug at the circuit board by pulling on the square plastic connector. Free the remainder of the cable from any tie-downs which may hold it in place until it simply hangs from the encoder itself.
   
2. Loosen and remove the four screws that hold the encoder module in place. These screws are usually very tight. Use a #2 Philips screwdriver for best results.
   
3. Remove the module by moving it toward the front of the machine. You will probably have to turn it a bit in either direction to get it clear of surrounding obstacles. Keep a mental note of the way in which you removed the module: you will reverse these movements to install the new one.
   

Generally, the ZBE Service Department requires that you return the failed module to the factory. We are always interested in why such unit would fail, and physical examination is the best way to find out. Please return your old module to the address at the end of this document.

INSTALLING THE NEW MODULE

Installation of the new encoder module is the reverse of installing the old one.

1. Hold the new Encoder Module so that the measurement cable exit snout points toward the rear of the machine. Hold the module near the Neg Stage where it will mount, and guide the end of the measurement wire through the rectangular hole in the rear wall of the Neg Stage compartment.
   

2. Manipulating the module as necessary, guide it into position until the four mounting holes line up. Keep an eye on the measurement wire to make sure it goes through the rectangular opening without being caught on any internal components inside the Neg Stage compartment.
   
3. Install the four screws that hold the module in place. Do not tighten them until you are sure that the measurement cable is not caught between the module's mounting bracket and the flange of the Neg Stage upon which it mounts. These screws should be very tight, since this module is the measurement reference for the Sentinel's Negative Stage.
   
4. Using a piece of thick wire (like a wire coat hanger) bent into a small hook, draw the measurement wire from between the Sentinel's column and the Neg Stage runner plate.
   
5. Draw the wire's end up to the top of the column and attach it to the top using the screw that held the old one in place. By positioning the eye at the end of the cable make sure that the cable runs perfectly parallel to the edge of the nearby rail. Tighten the screw.
   
6. Inside the Neg Stage compartment, connect the encoder's electrical connector to the Junction Circuit Board. Make sure that the white spot on the connector is on the same end of the connection as the small white "1" printed on the circuit board. Also make sure that all the pins are engaged, and that the connection is not one pin off center.

The new Encoder Module is now installed.

RE-INSTALLING THE ACCESS COVER

The installation of the Neg Stage's access cover is simply the reverse of it's removal.

1. Raise the cover, feeding the Zig-Zag cable through it's opening until it is in the same position as before the gray clamp was released. The cable will have a deformation where it was previously clamped. Fasten the clamp by pressing it together over the cable.
   
2. Move the cover in it's final position and very loosely install a couple of the 17 screws that hold it in place.
   
3. Examine between the cover and the Neg Stage housing to make sure that there are no cables or other items trapped between the two. When certain that all is clear, tighten the screws installed in the last step. (You may want to leave the remainder of the screws out until you test the new encoder.
   
4. Re-attach the Zig-Zag cable's guide wire to its point on the underside of the Neg Stage access plate.
   

The installation is now complete. You should test the new encoder using the following procedure:

1. Turn the power on, while pressing and holding the CANCEL key. This will bypass the Sentinel's normal "Referencing" procedure.
   
2. Once the main screen appears, go into the Diagnostics menu, item number 6, Test Reference Pulses.
   
3. While in this test, manually pull upward on the Neg Stage Encoder's measurement wire. You will need to pull it about 12 inches (30cm). While pulling it, every 5 inches (12cm), you should hear a beep from the keypad and a number will appear in the "COL" portion of the display. Keep pulling the cable out until you hear two beeps. The numbers for these beeps should be 4000 counts apart. If you never get a reading, or the numbers are not 4000 counts apart, re-check the installation of the encoder's measurement wire and the electrical connection inside the Neg Stage compartment.
   
4. If all checks out all right, reinstall and tighten all of the access plate screws. Note that the Neg Stage Access plate is a structural component of the Sentinel's Neg Stage assembly and the enlarger will be less accurate without all the screws installed and tight.
   

Getting back to work:

Now that the new encoder module is installed, the computer does not know where the machine is mechanically. This can cause some unexpected behavior from the Sentinel if you allow the machine to go into autofocus mode with the new encoder. Please observe the following steps to get the machine back on-line in a safe manner.

1. Turn the power on while holding the CANCEL key until "MANUAL" appears in the upper right corner of the keypad display.
   
2. Once the machine is up and running, it should be in manual-focus mode. Do Not put the machine into Autofocus mode. The lens setups which were done with the old encoder can cause erratic movements with the new encoder.
   
3. With the machine in manual-focus mode, go into the Sentinel Diagnostics menu and run the "Reference Enlarger" option. (Press MENU, <8>, ENTER, <7>, ENTER.) This will cause the machine to reference normally, but, since it is in manual-focus mode, we will avoid any erratic movements immediately after the referencing finishes.
   
4. At this point, you should immediately setup all lenses used with the machine before going into autofocus mode.

For any further questions or problems with this installation or any other ZBE product please contact us at: