CHECKS AND ADJUSTMENTS
6.7 READ/WRITE HEAD ADJUSTMENT
6.7.1 Head Alignment Check and Adjustment Requirements
Read/write heads are aligned initially when a drive is installed and after this only when any of the following conditions exist:
1. Read data errors occur.
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2. Any read/write head is replaced.3. Calibration stop is adjusted, replaced, or repaired.
4. Access transducer is adjusted, replaced, or repaired.
5. An alignment check reveals head out of alignment.
• 6. Temp Comp (PWA 18) is replaced.
The radial positioning of a read/write head during accessing must be precise to ensure disk pack interchangeability between drives. Head alignment checks are made to en
sure that positioning is accurate. The CE disk pack is used as a standard for checking head positioning and also for aligning a read/write head. Master cylinder 146 is the reference for the positioning check and alignment.
Reading any track of cylinder 146 of the CE pack produces an oscilloscope signal that forms two envelopes (lobes) as shown in figure 6-8. These lobes are used to produce a pulse with the trailing edge falling at the crossover point of the envelopes (figure 6-8).
Sync the scope to trigger on the positive-going transition of the sync pulse. Exact alignment is indicated when the trailing edges coincide,
6.7.2 Head Alignment Check Procedure
All 20 heads must be checked. The initial check is to be conducted following a 2-hour warmup to stabilize the drive. Use the following procedure to determine if head ad justment is required:
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1. Connect oscilloscope to drive and install the CE disk pack.Refer to steps 1 through 6 of paragraph 6.7.3.
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6—11
2. Use Off-Line Testor for accessing to cylinder 146 and for head selection
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(steps 7 through 10 of paragraph 6.7.3). Check heads consecutively 0 through 19.
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Figure 6-8. Waveform Pattern for Checking and Adjusting Heads
3. For each head, note the trailing edge of the pulses at the center cross over point. Refer to figure 6-8.
4. Pulse trailing edges must be superimposed. Otherwise, misaligned head must be adjusted.
NOTE: Head adjustment is performed only onmisaligned heads. After adjustment,
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however, all heads must be rechecked.
6.7.3 Head Alignment Adjustment Procedure
1. Install CE pack on drive.
2. Connect Off-Line Testor.
3. Ensure that the drive has been warmed up for two hours under the following conditions:
a. Top rear access cover removed.
b. Service access cover open.
c. Air duct removed.
d. All other mechanical components in place.
NOTE: When AC and DC power is removed for short periods of time during or just prior to head alignment, the drive should be restabilized for a period equal to twice the off time before continuing the procedure. In no case should the restabilization period be less than 5 minutes or greater than 2 hours.
6—12
VIEW A. HEAD OUT OF ALIGNMENT
VIEW B. HEAD CORRECTLY ALIGNED
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4. Connect jumper between 0601 and 0619.
5. Connect oscilloscope as follows:
a. INPUT 1 to 0613 (Test Point).
b. INPUT 2 to 0501 (Test Point).
c. TRIG IN to 0614 (Test Point).
d. SYNC on external (EXT).
6. Set up oscilloscope controls for the following:
a. Channels 1 and 2 chopped. Both inputs AC coupled.
b. Sweep triggered on positive slope of external pulse.
c. A vertical amplitude setting of 5v/cm for CH1 and 0. 5v/cm for CH2.
d. Sweep time as required for display of one disk pack revolution, approximately 25 ms (uncalibrated).
NOTE: Verify proper scope adjustment by gently pushing forward on the carriage and noting a change in the pulse pattern.
7. Perform seek to cylinder 146 with OFF-Line Testor.
8. Select head to be adjusted.
NOTE: Heads should be aligned from the bottom upward.
Alignment should begin with head 18 and end with
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head 1 on side A; alignment should begin with head 19 and end with head 0 on side B.9. Loosen clamp screw of applicable head. Tighten, using torque screw driver (P/N 70004459-1), to between 4 and 5 inch-pounds. See figure 6-9 for head location.
10. Using the alignment tool (P/N 70004055-1), adjust head position so that the trailing edges of the displayed pulses coincide to within 0. 1 cm.
11. Tighten head clamp screw to 7 inch-pounds. After removing the torque screwdriver, observe the oscilloscope display and proceed as follows:
a. If pulse coincidence pattern is more than 0. 1 cm out of alignment, repeat steps 9 through 11.
b. If pulse coincidence pattern is out of alignment but less than 0. 1 cm, proceed to step 12.
c. If pulse coincidence pattern has no observable offset, proceed to step 14.
12. Carefully press (forward and reverse) on carriage to determine direc tion of error in alignment. Then carefully insert the 70004055-2 alignment tool in head. This tool can be identified by the number 2 stamped on the handle.
NOTE: Do not allow the alignment tool camber to contact the head camming surfaces.
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SCREWS FOR LOADING
‘A’ HEADS
F
HEAD LOAD LINKS
F
TORSION RODS
‘B’ HEAD,7
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CLAMP
SCREW\
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0054 1/15/72
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Figure 6-9. Heads and T-Block
13. Gently rock the alignment tool in the same direction as the error oh-
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served by moving the carriage in step 12. Continue the alignment until there is no observable error in the pulse coincidence display.
CAUtION.
Exercise extreme care in performing the fine
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alignment to avoid breaking the alignment tool indexing pin. In no case should the alignment
procedure of steps 12 and 13 be used for an
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error of greater than 0. 1 cm.
14. Repeat steps 8 through 13 for the remaining heads to be aligned.
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15. Perform a post-adjustment check consisting of the following:
a. 100 restore operations
b. One unload-head load operation
16. Perform seek to cylinder 146 with f-Line Testor.
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CE
6—14 2341—2
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17. Select each head in turn and verify its alignment. Heads exhibiting pulse coincidence display errors of greater than 0. 1 cm should be realigned.NOTE: If any heads require the realignment of step 17, repeat steps 15 through 17.
18. Remove jumper from between 0601 and 0619.
6.8 INDEX TRANSDUCER ADJUSTMENT