Fujitsu M255XK Customer Engineering Manual page 47

4.4.7 Asymmetry
Tools Required: Work/Scratch Diskette
Exerciser (AVA 409 or equivalent)
Oscilloscope
Proceed as follows:
1. Connect the oscilloscope to the READ DATA interface signal (pin-30). Set
the oscilloscope range to DC mode, 2 Volts per division, and 1 microsecond
per division time base.
2. Start the Spindle Motor and load the diskette.
3. Seek the Read/Write head to the innermost track.
4. Record and then read a constant "IF" on the entire track (IF is a O's only
WRITE OAT A frequency of 125kHz for M2552K and 250kHZ for M2553/54K).
5. Measure asymmetry as shown in Figure 4-8.
Note:
READ DATA
IF cycl-e
-I:
I . . . . . . I---Asymmetry
Trigger
Figure 4-8 Asymmetry Measurement
Set the oscilloscope so 3 read data pulses can be observed and measured
on the screen, as shown in Figure 4-8.
6. At the innermost track, ensure the asymmetry is 600 nanoseconds or less for
the M2552K or 300 nanoseconds or less for the M2553/54K.
7. Repeat steps 4 through 6 for side 0 and side 1 •
. 8. If asymmetry standards are not met, the following items are probable causes.
(a) A high concentration of magnetic flux may be near the Disk Drive. If
there is a magnet, transformer, motor, CRT or other source of magnetism
near the drive, move it and repeat the asymmetry measurement.
(b) The diskette may be faulty. Replace the diskette and repeat.
(c) The Read/Write head may be faulty. Replace the head carriage assembly
(refer to paragraph 4.5.1).
(d) The main circuit card may be faulty. Replace the main circuit card
(refer to paragraph 4.5.6).
TS-021-013087 ••• 01
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