Technical Support Document 020 - 5/97

PROCEDURE FOR REPLACING SENTINEL NEGATIVE STAGE DRIVE MOTOR

The Sentinel Enlarger utilizes two drive motors in order to provide autofocus/autosizing operation. The Negative stage and the Lens stage each have a drive motor in them. The following procedure outlines the replacement of the Sentinel Enlarger's Negative stage drive motor.

NOTE: When a new motor is installed in the Sentinel enlarger, there is usually no need to re-calibrate any lenses, easels, or carrier setups.

REMOVING THE OLD MOTOR

Remove power from the Sentinel by unplugging the main AC power cord from the wall.
By gently moving the stages by hand, separate the negative and lens until the bellows is almost fully extended, at about 14" separation. This will ease access under the negative stage.

Remove the screw fastening the interstage cable guide wire to the underside of the negative stage. This is the steel cable which passes through a metal wire loop fastened to the zigzag shaped flat electrical cable between the stages. This wire is under spring tension, so be careful not to let it "snap" once the screw is removed.
Remove the negative stage access plate, on the bottom of the stage enclosure. Once the plate is free, the cable connecting the negative and lens stages will still be fastened to it. Unsnap the grey clip holding this cable onto the inside surface of the cover plate. Position the plate so that it rests on the top of the lens stage, letting the cable slide through the hole in the plate.

Locate the drive motor at the left, rear corner inside the negative stage enclosure. The motor will have two wire sets connected to it: the orange and gray twisted wires supply power to the motor, and the multi-colored bundle of wires connect to the motor's encoder, allowing the computer to monitor the motor's speed and direction.
Unplug the motor encoder wires (the multi-colored bundle) where they plug onto the negative stage junction board. Also unplug the coupling connector on the orange and gray twisted wires, pressing on this connector's locking lever to disengage it.
The motor and its attached mount are secured in place on two threaded posts with large hexagonal nuts. One of these posts will have a spring and a white block on it. To remove the motor, simply loosen and remove the large hexagonal nuts on both posts. In addition to the nuts, the spring and white block will come off the post that has them, and a metal spacer will come off the other. When all of these parts are removed, the motor mount will slide off the two posts, and will be free of the machine. See below:

INSTALLING THE NEW MOTOR

If the new motor does not have the black motor mount already screwed to it, transfer this mount from the old motor. It is held onto the motor by two screws. Be sure that the mount is installed on the new motor in the same manner as it was on the old one, and that the screws are tight. (The mount will only properly seat on the motor in one orientation.)
Position the new motor in place inside the negative stage. The single hole in the motor mount fits onto the upper of the two threaded posts inside the negative stage. Seat the motor mount fully against the rear surface inside the negative stage. Place the metal spacer onto the threaded and install the large nuts. Using both nuts will ensure that they do not loosen over time.
Place the white block over the other threaded shaft, such that it's angled surface mates with the similar angled surface on the motor mount itself. Next, place the spring, and then the first of the two nuts. Tighten the nut so that about ¼" (6mm) of the threads protrude through it. Install and tighten the second nut, holding the first so it does not get tighter against the spring while doing so.
The motor is now mechanically mounted. Re-connect both the motor power cable (orange and grey wires) and the motor encoder cable (multi-colored twisted bundle). On the encoder cable, make sure that it's connector is oriented correctly to the pins on the circuit board. The small white spot on the connector should be on the same end as the small "1" printed in white on the green circuit board.
Test the motor's mechanical action by moving the negative stage up and down the column a few inches. The motor pinion should not skip, and the movement should be smooth. Also verify that you hear the motor's gears turning as the negative stage is moved.
This completes the mounting of the new motor. The cover plate should now be installed. Be sure to clip the interstage cable back into the gray clip on the interior surface of the plate. Secure this cable into the clip at the same place that it was removed. There is usually an indentation in the cable left from being clamped in the clip; this will indicate the old position.
Screw the plate into position with just a few screws at this time, in case there is a problem with the installation of the new motor. Leaving the screws loose, inspect under the cover, looking for any cabling that is pinched between the cover plate and the negative stage body.
The enlarger's power may now be turned ON. Reconnect the AC power cord and turn the machine on. Immediately after flipping the switch, press and hold the "3" key on the keypad. This will cause the Sentinel to immediately enter its "TEST MOTORS" diagnostic.

In this mode, the arrow keys under the Enter and Cancel keys (the right-hand set of arrow keys) directly control the negative stage motor. Press and momentarily hold the Down-arrow. The Negative stage should move in a downward direction, and the readout on the keypad display for the "NEG" motor should read "DOWN."

If the movement is rough or noisy, the physical mounting of the motor should be double-checked. If there is no response, or if the display for the motor does not read "DOWN," the electrical connections to the motor should be double-checked.

Pressing the up-arrow key should cause the stage to move upward, and the display to read "UP."
When the motor checks out good, re-install the remaining screws in the cover plate, and re-install the interstage cable guide wire to the underside of the cover plate.
Press CANCEL on the keypad to start normal operation of the Sentinel. The machine will Reference as it normally does when turned on.

NOTE: If the new motor was sent as a replacement from ZBE, Inc., or a dealer, please return the defective unit to the factory at the address below.