Factory-Calibration; Read/Write Circuit; Head Ic - Fujitsu MAB3091FC Series Maintenance Manual

5.5

Factory-Calibration

Factory calibration is intended to correct errors in the mechanisms and circuits and maintain
stable seek, read or write operation.
(1) External force adjustment
Even if the actuator stops at a fixed position, disturbing forces such as an FPC force and air
movement caused by disk rotation are exerted. Also, when an instruction that reduces the
voice coil motor current to 0 is issued, a very small offset current flows in the control circuit.
Such disturbing forces are collectively handled, as external forces, by the control circuit. The
external forces depend on the disk type and actuator position. Self-calibration measures and
records external forces on the 128 representative cylinders, from the outermost to innermost
cylinder. To compensate for the effect of the external forces, the offset values that were
measured in each actuator position are applied to the circuit. This provides stable seek
operation.
(2) Servo gain adjustment
The servo control circuit gives stable operation when the gain of the servo loop is constant.
However, servo loop gains vary slightly, depending on each device and cylinder position
(outer, center, and inner cylinders) according to the characteristics of the magnet used in the
VCM. To compensate, the servo gain is measured at representative positions, from the
outermost to innermost, for each device.
adjustment. Measured values are stored, as a table, in flash memory. To adjust servo gain, the
DSP refers to this table, and creates a control table for constant loop gain. The DSP stores this
table in flash memory.
(3) Head position correction
When a write head is independent of the corresponding read head and both heads are driven by
the rotary actuator, the heads have different center positions depending on the cylinder
position. To compensate, the read head must be centered when writing. To adjust precisely,
the offset value for each head of each drive must be measured and stored in flash memory. At
correction, the DSP calculates the offset value for the head and cylinder position, and centers
the read head when writing.
5.6

Read/Write Circuit

The write/read circuit consists of a head IC unit (in DE), write circuit, read circuit, and a write
frequency adjust circuit. Figure 5.4 is a block diagram of the read/write circuit.
5.6.1

Head IC

The head IC is mounted inside the DE. The head IC has a preamplifier and a write current
driver, and has a write error detection function. Each channel is connected to each data head,
and is switched with a Head Select signal (HS0 to HS3). If a write error, such as a head short-
circuit or head disconnection is detected, an error signal (WUS) is generated.
Measurement is similar to the external force
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