Tandy 1400LT Service Manual page 225

Read/Write and control electronics
The FDD has following components.
(1) Index Circuit
(2) Head Position Actuator Driver
(3) Read/Write Amplifier and Transition Detector
(4) Write Protect Circuit
(5) Drive Select Circuit
(6) Standby Circuit
(7) InUse Lamp Circuit
(8) Voltage Detector
(9) Spindle Motor Start/Stop
(10) Track 00 Circuit
(1
1)
Side 1 Select Circuit
The Head Positioning Actuator moves the read/write heads to the desired track on the disk. The media cartridge is
loaded onto the read/write heads by an elevator mechanism with an oil damper when the cartridge is inserted.
Drive Mechanism
The brushless direct drive motor rotates the spindle at 300 rpm. Like conventional 5.25" drives, the FDD has a
MOTOR ON signal. Since almost all of the power of the FDD is turned off when the MOTOR ON signal is
"High", the power consumption in the standby mode is low.
the motor control circuit is printed on the Stator Yoke (material: iron) of the spindle motor and the Index Pulse is
generated by the hall sensor.
Positioning Mechanism
In order to achieve high accuracy in track positioning, the head is positioned by a lead screw mechanism. The
stepping motor rotates the lead screw clockwise or counter-clockwise and moves the read/write heads from track to
track.
If the heads is positioned at Track 00, Step signal to outer track is rejected.
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