The FDD Module is composed of the motor, sensor, magnetic head, and the IC that
drives them. The FDD Module is controlled by the FDC (#5) of the MAIN PCB.
10.3.1. Read/Write Circuit
In read operation, the circuit amplifies the analog signals picked up by the magnetic
head and converts the analog signal to serial digital pulses. The serial pulses are then
transmitted to the FDC (#5) and decoded to parallel digital data.
In write operation, the circuit controls the current at the magnetic head according to the
serial digital pulses from the FDC #5.
10.3.2. Motor Drive Circuit
The motor drive circuit consists of two parts: a DC motor drive circuit and a stepping
motor drive circuit.
The DC motor drive circuit controls the DC motor, which rotates the spindle according to
the MOTOR ON signal from the FDC. The stepping motor drive circuit controls the
stepping motor, which operates the magnetic head unit according to the "STEP" and
"DIRECTION SELECT" signals from the FDC #5.
10.3.3. Sensor Circuits
The following sensor circuits detect the status of the FDD:
1. Write Protect Sensor
When a write-protect notch on a disk is set to the write-protect position, the "WRITE
PROTECT" signal becomes LOW. A micro-switch is used for detection.
2. Index Sensor
The "INDEX" signal shows the beginning of a track; when the beginning of a track is
detected, the "INDEX" signal becomes LOW. A magnetic sensor is used for
3. Track00 Sensor
When the magnetic head is positioned in track 0 on a disk, the "TRACK 00" signal
becomes LOW. A photo sensor is used for detection.