CAUT ION
8.14 BRUSH DRIVE AND COMPONENTS
1. Place CB1 to OFF.
2. Remove top cover assembl3 and air dflcctor.
3. Unplug brush drive motor cable.
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4. Unclip three wires connected to the terminals on brush drive switch
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(snap action).
5. Remove three screws fastening brush drive assembly to baseplate.
INSTALLATION
Install brush drive assembly by reversing removal procedure.
8.14.2 Brush Retract Switch REMOVAL
1. Place CB1 to OFF.
2. Remove top cover assembly and air deflector.
3. Unclip three wires connected to terminals on brush drive switch.
4. Remove two screws threaded into nut plate below bracket and lift out
switch.
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INSTALLATION
1. Install brush retract switch by reversing the removal procedure.
2. Adjust brush retract switch according to paragraph 6.4.
8.14.3 Brush Drive Motor REMOVAL
1. Remove brush drive assembly.
2. Remove two nylon screws that fasten motor flange to drive brush mount.
This also removes ground wire that is also secured with one of these screws and a lockwasher.
3. Rotate motor counterclockwise so setscrew that secures brush rod arm to motor drive shaft becomes accessible. Loosen setscrew and slide motor shaft out of brush rod arm.
4. Remove drive motor and insulator from base of brush drive mount.
8.15 READ/WRITE HEADS (Figure 8-1) REMOVAL
1. Remove top cover assembly, EMA duct, and EMA cover.
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CAUTION
When performing maintenance on the read/write heads, where unloading/
loading is necessary, make certain that torsion rods are all properly po sitioned to avoid damage.
a. Move head load links up and down several times. There should be no binding.
b. With a flashlight anddental mirror held close to the head(s) (do not touch heads), examine torsion rods for proper positioning (see figure 5-3). They must be in correct position, with rod tips resting on load buttons. All cam follower surfaces of the head assembly must move freely within the head load cam.
2. Unload torsion rods.
a. Loosen two socket-head screws that fasten torsion rod retainer sup port to T-hlock.
b. Push downward on each torsion rod link until it clears retainer lip and hold.
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. c. Pull retainers toward heads, then gradually release pressure on link. This unloads torsion rods and thus releases pressure on head assemblies.3. Remove plug retainer (two screws).
4. Unplug read/write head to be replaced from matrix PWA connector.
5. Remove screw and washer securing head to T-block.
CAUTION
Protect read/write heads and torsion rods while performing steps 5 and 6.
6. Pull head from array carefully toward back and to side from rear of cam tower. Do not flex assembly unnecessarily; preset alignments may be altered.
CAUTION
a. Do not touch gliding surfaces; acids from skin will etch and disfigure surface.
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b. Do not touch face of head with fingers;
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oil from skin can cause build-up of deposits. Do not leave lint or residue onheads. Donotblowonheads; mois ture from breath can cause contamina tion.
c. Do not use volt-ohmmeter to verify continuity through head elements; VOM voltage is sufficient to burn out elements.
d. Do not lay head on EMA; induced magne tism can affect read/write operations.
e. Do not use a head if any distortions or abnormalities are evident; replacement is cheaper than lost data.
f. Clean read/write heads only when in spection reveals presence of oxide de posits. Refer to Chapter 5, Mainte nance, for cleaning instructions.
INSTALLATION
NOTE: Four different read/write head configurations are used in the drive: BTJ, BD, AU, and AD.
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Each head configuration is assigned a differ- -‘ Li ent part number and is not interchangeable
with other part numbers. Refer to figures 4—11 and 6-9 for further details.
Examine replacement head to ensure that it is same part as one removed.
Clean gliding surface with lint-free tissue moistened with 90% isopropyl alcohol.
CAUTION
Read/write heads are delicate. Use extreme care in handling new head arm assembly to position it in T-block slot. Ensure that tor sion rod is correctly positioned against dimple
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on arm assembly. Avoid contact between head gimbal and cam.
2. Locate cam surface of replacement head in cam tower and position the tip of arm in T-block slot. Ensure that head assembly is seated pro perly before installing mounting screw.
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3. Install single mounting screw and washer to secure head arm to T-block.
Do not tighten at this time.
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4. Manually move carriage back-and-forth while checking cam surfaces for correct mating action.
5. Plug read/write head into matrix PWA connector.
6. Replace plug retainer.
7. Manually retract carriage and load torsion rods by reversing procedure 8.15, REMOVAL, step 2.
8. Perform head alignment check and adjustment procedure of paragraph 6.7.
8.16 ‘A’ MATRIX PWA’S (Figure 8-2) REMOVAL
1. Turn off disk pack and wait until disk pack stops rotating.
2. Open operator cover and remove disk pack.
3. Remove top cover assembly and EMA duct.
4. Extract top screws and loosen lower screw securing head-plug retainers to cam tower and remove retainers.
5. Unplug all head plugs to matrix card connector. Also, for matrix card connecting to “A” side heads, remove ground strap.
6. Loosen matrix card retainer screw enough so retainer may be turned to allow matrix card to be extracted.
7. From shroud side of cam tower, unplug matrix card by applying upward force to bottom of both sides of card.
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8. After card is unplugged, grasp top of card and pull upward and out of card tower.INSTALLATION
Install matrix card by reversing removal procedure.
8.17 CAM TOWER (Figure 8-1) REMOVAL
1. Remove top cover assembly, shroud, EMA duct, and both matrix cards.
2. Remove two matrix card sockets (two screws fastening each socket).
3. Unload torsion rods. See 8.15.
4. Remove four head-arm cams (two screws fastening each cam to cam tower).
5. Extract top screws and lower screw securing head plug retainers to cam tower, and remove retainers.
6. Unplug all heads to matrix card connector. Also, for matrix card con fleeting to “A” side heads, remove screw attaching topmost cable (car riage ground) from head assembly to “A” matrix card.
7. Remove four screws securing cam tower to baseplate.
8. Lift up cam tower enough to clear pins on baseplate, pull forward and away from baseplate.
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INSTALLATION
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1. Position cam tower so two locating pins in baseplate protrude into corres-ponding location holes in cam tower feet.
2. Complete installation by reversing steps 1 through 7 of removal procedure.
NOTE: When attaching carriage ground cable to matrix card bracket, place attach ing lockwasher between terminal lug and bracket.
8.18 EMA MAGNET (Figure 8-1) REMOVAL
NOTE: Remove your wristwatch to keep the intense magnetic field from affecting watch regulation.
1. Place CB1 to OFF.
2. Remove top cover assembly, EMA duct, EMA cover, and rear skirt.
Rear skirt is fastened with five screws and lockwashers.
3. Disconnect EMA cable clamp (one screw) and two wires to EMA flex
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ductor (one screw each).
4. Unload torsion rods per 8. 15.
5. Remove four screws securing T-block to EMA coil cap.
6. Remove three bolts fastening EMA to baseplate.
7. Gently lift EMA while pulling away from T-block to disengage slot in EMA base from locating stud on baseplate.
INSTALLATION
1. Clean lower surface of EMA base and mating surface of baseplate with lint-free tissue dampened with 90% isopropyl alcohol.
NOTE: There must not be any particles between EMA base and baseplate. Otherwise, spurious noise effects may be present in critical signals during operation of disk drive.
2. Complete installation by reversing removal procedure.
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8.19 EMA COIL (I9gure 8-5) REMOVAL
1. Remove EMA magnet (see paragraph 8. 18).
2. Remove two screws, fasteners, and lower flexure supports from coil.
3. Pull coil out of front of EMA housing.
INSTALLATION
1. Install EMA coil by reversing removal procedure.
8.20 TORSION RODS (Figure 8-1) REMOVAL
1. Place CB1 to OFF.
2. Remove top cover assembly, EMA duct, and EMA cover.
3. Unload torsion rods per 8. 15.
4. Remove four screws fastening T-block to EMA coil cap.
5. Move carriage away from EMA coil.
6. Remove the clip and washer which secure the torsion rod to the head load link (figure 4-12).
7. Remove the torsion rod by pulling it through the T-block.
821 ACCESS TRANSDUCER (Figure 8-5)
Three operational parts of the access transducer are replaceable: secondary grating,
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source mount, and sensor mount. Because the source and sensor mounts are matched for functional reasons, they must be replaced as a matched pair. Whenever any of these operational units are replaced or their positioning is disturbed, the access transr
ducer adjustment described in paragraph 6. 2 must be performed.Replacement of the access transducer insulator, which functions as a protective cover and not as an operational part, does not necessitate adjustment.
REMOVAL
1. Place CB1 to OFF.
2. Remove top cover, EMA duct, EMA cover, and shroud.
CAUTION
Protect read/write heads and torsion rods.
3. Unload torsion rods per 8. 15, REMOVAL, step 2.
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4. Remove “A” side plug retainer (two screws). Top screw requires removal;
lower screw need only be loosened.
5. Disconnect “A” side head plugs and carriage ground assembly (latter is secured by one screw and washer).
6. Twist connector latch counterclockwise to disconnect source and sensor harness from plug bracket (on air deflector support).
7. Remove two screws and nylon washers securing source block to sensor mount, and lift source block disengaging from dowels on sensor mount.
CAUTION
When handling primary and secondary gratings, avoid touching graticule.
8. Remove primary grating (three screws and two clamps).
9. Remove two corner screws securing sensor mount to mounting block.
Loosen adjusting screw on sensor mount approximately six turns counter clockwise. Lift off source block, disengaging from dowels on mounting block.
10. Desassemble secondary grating from sensor mount (two screws).
INSTALLATION
1. Assemble secondary grating to sensor mount, carefully tightening screws until they are snug.
2. Attach matched source and sensor mounts to mounting block, tightening screws until snug. It may be necessary to turn adjusting screw on sen sor mount a couple of turns clockwise to get sensor mount to properly seat on mounting block. Do not force this seating. It is better to remove adjusting screw, replacing later after seating sensor mount.
3. Attach primary grating to carriage carefully and incrementally tighten screws in succession until fully tightened.
4. Connect source and sensor harnesses to plug bracket, twisting connector latch clockwise to engage.
5. Adjust clearance between primary and secondary gratings according to 6.2.
6. Perform parallelism adjustment, cylinder position adjustment, and equip ment close-up according to 6. 2.
NOTE: Head alignment must always be checked after alteration of any operational com ponent in access transducer (see 6. 7).
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8.22 PRIMARY GRATING