Technical Support Document 052 - 8/97

TEST LIMIT SWITCHES DIAGNOSTIC

The Sentinel Enlarger (and Satellite universal scanner) utilizes motorized movement to facilitate it's autofocus operation. To keep the machine from damaging itself through errant motorized movement, the system uses three limit switches to tell the computer when any of the moving parts has exceeded the physical limits of travel. There are three limit switches on the machine:

Top Limit: Stops the head stage from running off the top of the column in an upward direction. The switch itself is mounted behind the head stage column runner plate.

Bottom Limit: Keeps the lens stage from running into the baseboard (or off the bottom of column on wall-mounted machines) in a downward direction. This switch is mounted behind the lens stage runner plate.

Bellows Limit: This limit switch tells the computer when the two stages (head and lens) have come together all the way with the bellows fully collapsed. This switch is mounted behind the bellows on the underside of the head stage.

Two of these three limit switches are used during the machine's Referencing procedure. If the machine does not complete the referencing process, it is usually a good idea to check for the proper operation of the bottom limit switch and the bellows limit switch.

The procedure follows:

1. Move the two stages (head and lens) of the machine to a convenient location about a third of the way up the column. Separate the bellows by about 8 inches. You may push the stages slowly by hand.
   
2. Turn the machine on, if it is not already. If the machine will not complete the "Referencing" procedure upon power-up, turn the machine off, then on again, this time holding the ENTER key until the word "MANUAL" appears in the upper right-hand area of the keypad display.
3. Access the Sentinel (or Satellite) Diagnostics menu, and run the "Test Limit Switches" diagnostic. (See user's manual for menu descriptions.)
   The keypad display should show the status of four limit switches: "BELLOWS," "TOP," "BOTTOM," and "EXTRA." All readings should say "OFF" at this time.
   
   

4. Test the TOP limit switch using an un-sharpened pencil or similar object: From above, insert the pencil between the column and the head stage runner plate, following the right-hand rail on the column. You should be able to make the switch "click" using the pencil.
   

5. When you hear the switch "click," the display for the "TOP" limit should change from "OFF" to "ON."
   
   

6. Repeat this test with the "BOTTOM" limit switch, using a pencil inserted between the lens stage runner plate and the column, from below.
   
7. When you hear this switch click, you should see the display for the "BOTTOM" switch change from "OFF" to "ON."
   
   

8. Test the "BELLOWS" limit switch by pressing upward on the small wire striker behind the bellows. This striker for the Bellows Limit Switch is located on the underside of the head stage, directly behind the bellows, where they run up into the bottom of the neg stage platform.
   
9. When you hear this switch click, the display for the "BELLOWS" limit should change from "OFF" to "ON."
   
   

10. If any three of the switches does not change when you make it "click" by physically pressing it, the wiring to that switch should be examined. Please contact your dealer, or ZBE.