Technical Support Document 011 - 2/96

REPLACING SENTINEL MOTORS AND MOTOR PINION GEARS

This document covers the removal and installation of either Motor in the ZBE Sentinel Enlarger. The changing of the pinion gear on these motors is also covered.

MOTOR REMOVAL

The removal of either motor requires the removal of the cover plate on it's respective stage enclosure. The locations of these plates is as shown at right below:

The Lens Stage Cover Plate is secured onto the bottom of the Lens Stage enclosure with about twelve screws.

To remove the Neg Stage Cover Plate:

Separate the Lens and Neg Stages by at least 10 inches (maximum 14 inches). Remove the power plug from the wall socket.
Loosen and remove all screws. There are about 19 screws that hold this plate in place.
Once the Plate is free, carefully lower it. You will see several flat cables inside the enclosure among other wiring.
Release the cable clamp holding the Interstage Cable (the zigzag formed flat cable behind the bellows that attached to the Lens Stage) so that it is free of the plate.
Slide the plate downward along this zigzag cable until it reaches the wire-formed clip that guides the flat cable along the steel wire under tension.
Let the plate rest in this position for the remainder of this procedure.
There are many fragile wires inside these enclosure compartments, so please be careful when working within them.

Inside the stage compartment, once the cover plate is removed, the AF Drive Motor for that stage will be visible in the left-hand area of the compartment. Note that the motor is secured at two points, one has a long post or screw with a white block near it's base, the other a short screw that simply holds the motor mount plate onto the stage plate. There are two configurations possible:

Before loosening motor mounting screws/nuts for motor removal, disconnect both the orange-and-grey motor power wire, and the multi-colored encoder wiring. The motor power wire disconnects at it's in-line locking connector, and the encoder wire plugs into the square green circuit board mounted to the "roof" of the compartment. Be sure to keep the spring and white block, and to note their orientation before removal.

Once the Motor is free of the enclosure, examine the pinion gear on the end of the motor shaft. It should not have any missing or partially-missing teeth. It is normal for the pinion to have some wear, but the wear should be even on all teeth.

If the pinion is in need of replacing, it will need to be removed from the motor shaft. On older Sentinels, the pinion is "pinned" onto the motor shaft. This is a method of attachment that will require a hammer and a "pin-punch" for removal. Newer Sentinel pinions are attached using three allen-head (hexagonal drive hole) set screws. Pictures of the two types are shown below:

After removing the old pinion, if it was in need of replacement, the new pinion is installed by positioning it on the motor shaft. All new pinions will have the brass collar that has three set screws in it. Place the new pinion onto the shaft, as shown below, using the spacing tool to ensure proper pinion mounting height. You must remove the black motor mount plate for the spacing tool to work properly. This is easily done by removing the two screws holding it on. If the motor shaft has a flat on it, place the new pinion so that two of the three set screws straddle the flat area (see below); failure to do this will cause the pinion to be crooked.

Once the new pinion is installed, inspect the assembly to ensure that is is straight. A pinion mounted crooked on the shaft may cause problems with autofocus operation. When straightness is verified, tighten all three set screws extremely tightly, working the screws a little at a time, going from one to the next in succession. All three screws should be of equal tightness, and all three must be very tight.

If your motor has a pinion that is "pinned" in place (with the roll pin, not set screws), and a flat on the shaft, you may contact ZBE for a replacement motor if you do not feel comfortable with taking the old pin out, do not have the tools to do so, or just cannot get the new pinion on straight.

Once the pinion is tightened in place, re-install the black motor mounting plate onto the face of the motor. Once this is done, the motor may be re-installed in the enlarger. When doing this, it is recommended that you place the motor in position, and install the screw (or nut) that holds the motor pivot point first. This will keep the motor in position while installing the white tensioner block and spring. When securing this first point, fully tighten the fastener (nut or screw), and check that the motor can rotate slightly, but is not so loose as to be able to move away from the runner plate to which it is fastened.

Once the motor is re-installed in the enlarger, move the stage up and down by hand to check the smoothness of the pinion's engagement into the rack on the face of the column. The travel should be relatively smooth, and the pinion should not skip teeth on the rack under any circumstances.

The motor is now re-mounted. At this point all that is left to do is re-connect the cabling, and re-install the cover plate. Please note the following:

The Motor Power plug only plugs in one way, so you can't get it backwards.
The Encoder plug, however, must be aligned with the connector on the junction board inside the stage. Be sure to plug it into the pins labeled "MOTOR ENCODER."
The white mark on the motor's encoder connector must be positioned at the same end of the connector on the board indicated with a number "1" printed in white on the green circuit board.
Be sure that this connector is positioned squarely on the pins, and is not one pin off.
When re-installing the cover plate to the stage in which you re-installed the motor, be sure not to clamp any wires or connectors between the plate and the surface to which it mounts. This is particularly notable with the Neg Stage, since there is alot of different wires within.
If you were working inside the Neg Stage, when re-installing the cover plate, do not forget to re-clamp the zig-zag cable onto the clamp attached to the cover plate.

Test that the replaced motor is functional by performing the TEST MOTORS diagnostic in the Sentinel Diagnostics menu. The procedure is as follows.

Go into TEST MOTORS in the Sentinel Diagnostics menu. (Press MENU, <8>, ENTER, <3>, ENTER.)
Press the Up arrow corresponding to the stage you just worked on. That stage should move upwards, and the keypad's display should read "UP" for the stage. This procedure is also outlined in your user's manual.
Once verified, the enlarger is ready for normal operation.