Viper 60s Theory Of Operation And Maintenance Manual page 143

VIPER 8C8160, 125 & 150 THEORY OF OPERA TION AND MAINTENANCE
6.5.2 Write Protect
The cartridge sidewall includes a rotating safe switch that
is
solid on one side and hollow on
the other. When the safe switch is rotated so the solid side faces toward the write protect
microswitch, this solid portion actuates the write protect switch and permits writing on the
tape. When the safe switch
is
rotated so the hollow side faces the write protect microswitch,
the switch is not actuated, and write or erase functions are not permitted.
6.5.3 Tape Hole Sensors
An optical end-of-tape sensor assembly is included in the Viper drive. This assembly consists
of an infra-red LED placed near the edge of the cartridge.
• A light beam from the LED shines through a plastic window in the cartridge.
• The beam is reflected 90 degrees by a mirror back through the window in the
cartridge onto two infra-red detectors adjacent to the LED. Normally the beam is
blocked by the tape as
it
moves across the head. Near each end of the tape are small
diameter holes. When these holes pass in front of the light beam, the beam can pass
through the hole and be sensed by the infra red detectors.
• These holes are located to indicate an end of tape or beginning of tape condition.
Tape holes are placed at different locations depending on end of the tape involved
with two detectors used to determine the end of tape being sensed.
6.6 Motor Driver Printed Circuit Board
The Viper motor driver printed circuit board drives a three-phase, four-pole, brushless motor
with eight-pole tachometer. All functions for controlling the speed and directions of this
motor are contained on this circuit board, with the exception of certain control functions
which are handled by the VLSI located on the Main PCB. A block diagram of the Motor Driver
PCB is shown in Figure 6-3.
6-12