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Theory of Operation
3-3
Figure 3-3:
Head Positioning Assembly
Index Pulse Shaping Network
The index pulse circuitry consists of an index LED, photo transistor and pulse shaping
network. The index hole in the flexible disc passes between the index LED and photo
transistor, causing the photo transistor to conduct. The detected signal is then shaped and
buffered and output on the Index Pulse interface line (J 1-8). This signal although inverted
may be observed at TP7 on the drive electronics board.
Write Protect Sensor
The write protect sensor consists of a switch which is opened when a write protected disc is
inserted into the drive. This signal is delayed by an RF filter to eliminate transient noise from
the switch. This will cause the write protect line (Jl-28) to go low and TP9 to go high.
Track 0 Switch
The level on the Track 0 interface line is a function of the head assembly position. When the
head assembly is positioned at track 0 and the stepper motor indicates phase 0, J4-19 is
pulled low, causing TP8 and the Track 0 interface line to be pulled low.
Spindle Motor Drive Control
The spindle drive system consists of a spindle assembly driven by a DC motor-tachometer
combination and the servo electronics board.
The servo electronics includes a current limiter and interface control line.
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