Technical Support Document 053 - 8/97

TEST REFERENCE PULSES DIAGNOSTIC FOR AUTOFOCUS SYSTEM

INTRODUCTION

The autofocus system in the Sentinel enlarger and Satellite Universal Scanner utilizes two optical encoder modules for determining the exact positions of the lens and neg (head) stages. One encoder, located to the right of the lens mounting area, reads the distance between the negative or scanning plane, and the lens. The other encoder, located within the neg stage, reads the position of that stage relative to the baseboard.

The encoder modules measure these distances to within 1/1000 inch. Each module utilizes a thin steel cable to make it's measurements. These cables are visible within the bellows, and running along the right side of the front of the column above the neg stage.

Testing the encoder modules entails a diagnostic routine where each cable is pulled by hand from its module, the verifying that the numeric readout from each module changes appropriately. The procedure follows:

PROCEDURE

Move the lens and negative stages all the way to the bottom of the column, either using the jog arrow keys on the keypad, or by gently pushing them with the power off.
Separate the bellows by about 12 inches, to gain easy access to the space between.
At the keypad go into the TEST REFERENCE PULSES diagnostic (Item #6) that is found in the SENTINEL (or SATELLIITE) DIAGNOSTICS menu.
Lift the bellows from the bottom, separating the velcro. The top of the lens turret will now be visible, as well as a thin stainless steel cable the runs from a hole to the right of the lens turret area, up into the bottom of the neg stage, then back down near the front, right-hand corner of the lens turret area.
The screen will show something like what is shown below.

Grasp the steel cable under the bellows, where it comes down at the left front corner of the lens turret area. (See drawing below.) Be extremely careful not to bend or kink the cable in any way. Pull down, drawing the cable slowly downward.

While you do this, watch the top line of the display. At some point, a number will appear, replacing the dashes. This number should appear, with a beep from the keypad, within about 5 inches of cable travel.
When this happens, continue pulling the cable in the same direction, until another beep is heard. A new number will appear, replacing the old one.
At the second beep, compare the two numbers-they must be exactly 4000 counts apart. For instance, if the first number was 12345, the second should be 16345.
If the keypad never beeps, the encoder's reference pulse is not reaching the AF Computer Box, or the encoder itself is faulty. Check all the connections between the Lens Stage and the Neg (head) stage.
If the number changes by an amount other than 4000 counts, try this test repeatedly. If the number continues to change by an amount other than 4000, then the Encoder Module will need replacement. (Note that pulling the cable at different rates of speed can cause small differences in the count of 4000, but not more than a point or so.
After satisfied that the reference pulse is working, slowly move the cable back to it's original position. Do not let the cable "snap" back into position. This may destroy the encoder module. Note that moving the cable in the other direction will change the number by about four counts. This is normal. Pulses (and the beeps/number-changes) going in the same direction, will result in a constant change of 4000, every 5 inches of cable travel.
If this encoder performs as indicated, test the column encoder in the same manner. First, grasp its cable and pull upwards while viewing the keypad. This cable can be found running along the right-hand rail mounted to the front of the column.
Again, a beep should be heard every 5 inches of cable travel, and the number (this time on the bottom line of the display) should change by 4000 for every beep while pulling the cable in the same direction.

For any questions or problems, please contact ZBE.