CHECKS AND ADJUSTMENTS
6.2 ACCESS TRANSDUCER ADJUSTMENTS
Three adjustments are required after alteration or removal of the assembly or any of its components (Figures 6-1 and 6-2):
1. Grating Proximity: The grating proximity is adjusted so the distance between the bottom glass surface of the primary grating and the top glass surface of the secondary grating is between 0. 002 and 0. 005 inch (Figure 4-5). This distance is adjusted by placing shims under the sensor mounting block.
SOURCE MOUNTING BLOCK
SENSD’R
--Figure 6-1. Access Transducer Assembly Locations 2341—2
6—1
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2, Parallelism: The lines on the primary grating must be parallel with the lines on the secondary grating. This produces a pattern as shown in View B of figure 6-3. A lack of parallelism produces a moire pat tern as shown in View A of figure 6-3. The parallelism adjustment is made by manually positioning the primary grating so its lines are para llel with the lines on the secondary grating.
INSULATOR
INSULAT1NG WASHER SOURCE MOUNTING BLOCK
CYLINDER ADJUSTMENT SCREW UNDER INSULATOR
INSULATOR
11
SENSOR MOUNTING BLOCK 14
SECONDARY GRATING
SHIMS ARE PLACED UNDER BLOCK
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Figure 6-2. Access Transducer Assembly
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GRATINGS NOT PARALLEL (MOIRE’ PATTERN) VIEW A
Figure 6-3. Grating Assembly Patterns 6 —2
GRATINGS PARALLEL VIEW B
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2341—2
3. Cylinder Position: The cylinder positioning is checked by placing a 0.038—inch shim between the carriage and the calibration stop (figure 6-4). The shim is held in place by exerting a slight hand pressure against the carriage. Under these conditions, the last velocity line on the primary grating must fall within (not necessarily centered in) the index line on the secondary grating (figure 4-6).
6.2.1 Preparation
Figure 6-4. Carriage Assembly
SPINDLE 1/15/72
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2341—2
1. Place START/STOP switch to OFF.
2. Remove both rear access panels. Obtain permission to stop DP oper ations and place CB1 to OFF.
3. Remove disk pack if one is installed.
4. Remove entire top cover assembly.
5. Remove shroud, EMA shield, and air duct.
FRONT SCREW
MOVING CYLINDER INDICATOR SCALE
HEAD LOAD LINKS
CARRIAGE RETRACT SWITCH ACTUATOR BAR
REAR SCREW
FORWARD SCREW
SWITCH BUTTON CARRIAGE
RETRACT SWITCH
CALlB RAT ION STOP
6—3
1’
6. Carefully move carriage forward until head load links just clear car riage interlock bracket (approximately 1-1/2 inches).
CAUTION
Carriage must not be extended far enough
F
for heads to start down cams. Extreme head damage will occur if heads leave cam sur face without a pack in place, and rotating.
If accidentally moved too far, heads must be carefully inspected before subsequent use.
7. Unload torsion rods by loosening two screws on top of T-block.
8. Remove head cable plug retainer from “A” side.
9. Disconnect head cable plugs from “A” matrix and lay aside. (Tape
L
placed around the entire set of cables will aid in keeping them out of the way).
10. Remove two screws and insulator from source mounting block (Figure 6—2).
11. Lift off source mounting block and lay aside. Remove insulator under source mounting block.
6.2.2 Grating Proximity Adjustment
C
Perform an initial check to verify that a 0.002- to 0.005-inch clearance exists between primary and secondary gratings at the minimum clearance point.
F
1NOTE: Use only nonmetallic shims for making
this measurement.
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The minimum clearance point is determined by moving the carriage through its full travel and noting the point location where clearance exists between gratings. If clearance is not within limits, adjust as follows:
1. Ensure primary grating is secured in place and sensor mounting block mounting screws are tight. Observe clearance between gratings (see figure 4-5). Estimate thickness of shim required to bring gap into range. It may be necessary to use a combination of several nonmetallic shims to measure the gap.
2. Place 0.002-inch measureing shim between gratings and loosen (don’t
remove) primary grating hold-down screws and two cap screws holding
F
down sensor mount. These screws must be loosened enough to allow spacing shims to be slipped under sensor mount (see figure 6-2).
3. Select several spacing shims to obtain required thickness determined from step 1. Initially, use at least 0.002—inch less than estimated because shims will vary slightly in thickness and may not be the exact value printed on them.
6—4 2341—2
4. Retighten sensor mounting block screws, then lightly tighten primary grating screws. While tightening, check with 0.002-inch measuring shim to ensure gap is not less than 0.002-inch. Do not move carriage while tightening screws.
5. If more than 0.002—inch gap exists, check for 0.002- to 0.005—inch gap per original checking method. If less than 0.002—inch gap exists, go immediately to step 2 and remove required number of spacing shims to increase gap to 0.002-inch minimum. Repeat steps 1 through 5 until 0.002- to 0.005-inch gap exists between gratings at minimum clearance.
6.2.3 Parallelism Adjustment
NOTE: Use small penlight to eliminate shadows in transducer area.
1. Position carriage forward until primary grating is approximately cen tered over secondary grating.
2. Loosen three screws holding primary grating in place (figure 4—5).
3. While observing from directly above, position primary grating until exact parallelism of line is obtained. No moire patterns should remain.
4. Start with rear screw and successively tighten three screws holding
Q
down primary grating. Tighten screws in increments while equalizing torque to maintain a relatively level attitude of the primary grating.Tighten the rear screw (with raised shoulder) to 5 to 6 inch-pounds and the other two screws, to 4 to 5 inch-pounds.
CAUTION
Uneven tightening of primary grating screws may break glass on which the lines appear.
6.2.4 Cylinder Position Adjustment
1. Move carriage to calibration stop.
2. Place 0. O’38-inch feeler gauge between carriage and calibration stop (figure 6-4). Hold in place with slight hand pressure on carriage.
3. Insert 0.002-inch protective shim between gratings and loosen cap screws on sensor mounting block (see figure 6-2). Loosen screws just enough to allow block to be moved.
4. Rotate cylinder adjustment screw CCW approximately two turns while forcing sensor mounting block toward EMA. Do not allow adjustment screw to move block. Remove 0.002—inch shim from between gratings.
5. Adjust cylinder adjustment screw until leading edge of last dark line of the velocity grid on primary grating is within velocity index line on the
U
2341—2 6—5
B
secondary grating (see figure 4-6).
NOTE: The adjustment must always be made byrotating cylinder adjustment screw CW.
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In event of adjustment overshoot, repeat steps 4 and 5.
6. Remove 0.038-inch shim between carriage and calibration stop.
7. Move carriage forward until it just makes contact with calibration stop.
Hold in place with slight hand pressure.
8. While observing cylinder vicinity segment, carefully adjust cylinder adjustment screw until cylinder vicinity segment grid becomes gray, position 1 segment grid is black, and position 2 grid is white.
NOTE: Due to parallax, it is necessary to observe this condition from directly above, with
only one eye.
[1
9. Tighten mounting screws and verify that conditions established by step 8 are not disturbed.
10. Install 0. 038-inch shim between carriage and calibration stop and ensure that leading edge of last dark line of velocity grid is within (not neces sarily centered on) velocity index line on secondary grating. If not, re-peat adjustment starting with step 1.
6.2.5 Equipment Close-Up
1. Install plastic insulator over sensor mounting block.
2. Install source mount with insulating washers and screws.
3. Replace head cable plugs and head plug retainers.
4. Move carriage back against interlock bracket and load torsion rods.
Return carriage to fully retracted position after loading heads.
CAUTION
Use a dental mirror to inspect all heads to ensure that torsion rod tips are positioned against load buttons on heads and are not locked together. Incorrect torsion rod pos itioning may result in physical damage to heads.
5. Replace EMA shield, shroud, and air duct. V
6. Install top cover and both rear access panels.
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NOTE: Head aligmnent must always be checkedafter alteration of any component in
C’
access transducer.
6—6 2341—2
7. Perform head alignment after completing access transducer adjustments.