Teac FD-55 Series, Maintenance Manual

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Drive select gate classifies the external input signals into several
functions and transmits them into the control LSI.
The selection of straps (short bars) determines the select condition
of the drive, head load and spindle motor operating conditions, and
turn-on condition of the front bezel indicator. Refer to items 1-11
and 1-12 of the Specification as to the detailed function of each strap.
The head load gate, adding the pre-ready condition to the selected head
load command by the drive select gate, turns on the solenoid driver,
The head load gate also triggers the internal over-drive timer
constructed with a re-triggerable counter and maintains the over-drive
circuit on for a determined period (26msec,approx.). During this period,
rf 12V power is applied to the head load solenoid to execute the drawing
action of the solenoid stably. -
To protect the head positioning error by the impact of the head loading,
the stepping motor is also over-driven. After the completion of the
over-driving, both the head load solenoid and the stepping motor are
maintained by +5V power to minimize the power loss.
The write/erase gate judges the FDD whether it can execute¿write
operation or not and issues write gate and erase gate -signals for the
write circuit. A specified delay time is established in the erase
gate signal by an internal counter (refer to Fig,306). ^
The ready detector consists of speed detector, pre-ready latch, and
ready latch. The output of the speed detector which is constructed
with a re-triggerable counter becomes always TRUE (HIGH) when the
rotational speed of an installed disk (soft sectored) is more than
50%, approx. of the rated speed. The pre-ready latch detects the
first index pulse (pre-ready condition) after the speed detector
detects the 50% of the rated speed. The output of the ready latch
becomes TRUE (HIGH) when the second index pulse after the 50% of the
rated speed, then the READY condition is informed to the host system
through the output driver, U2 (pin 1 ^ 3 ) .
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