MPI 40 Series - Track 00 and Track 43 Sensors; Index Sensor; 3.4.6 Activity Indicator; 3.4. 7 Read;Write Heads

3.4.4 Track 00 And Track 43 Sensors
These sensors are used to convey head position to the controller
through the control electronics PCBA. By monitoring these two
sensor outputs, head position can be determined to be at track 00;
between track 00 and 43; at track 43 or greater.
3.4.5 Index Sensor
The index sensor is mounted on the bottom of the drive and is used
to inform the control electronics PCBA when the index hole in the
diskette is present. The index hole is used to reference the
beginning of a track. The index period is also used to determine
whether the diskette is rotating at its nominal speed. If the
diskette is not up to speed, in the standard configuration the head
will be unloaded and the not ready signal will be sent to the
controller.
3.4.6 Activity Indicator
The activity indicator is an LED which is mounted in the drive
bezel. This LED is illuminated by the control electronics PCBA
when the drive has been selected.
3.4. 7 Read/Write Heads
The Model 41 has a single read/write head for the lower diskette
surface only. This head is held in the carriage in a fixed atti-
tude, and its surface has a spherical contour. In this model, when
the head load solenoid is activiated, a pressure pad applies a
gentle (20 grams) force which pushes the diskette against the
head.
On the Model 42 drive, the pressure pad is replaced by a second
read/write head which is mounted on a gimbal spring, and is there-
fore allowed to change its attitude as required to minimize both
head and media wear. On this model, both heads have a special
"blended" contour which also helps reduce wear. In both cases, the
read/write heads are single element ceramic.heads with tunnel erase
elements to provide erased areas between adjacent data tracks.
Without this erase capability, interchange tolerances between media
and drives can degrade the signal to noise ratio. Thus the erase
mechanism significantly enhances diskette interchangability.
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