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806-0331-100
MODEL 331 TRANSPORT ELECTRONICS
CIRCUIT DESCRIPTION
This schematic includes the Transport Electronics
board, Write Head Driver board, Read Heads, Write
Heads, Capstan Motor and Tachometer, and the A
and B hole photo sensors.
The functions of the Transport Electronics board are
as follows:
1.
It
generates the ramp output to the capstan motor.
2.
It
amplifies the
A
and
B
holes detected by the
A
and
B
photosensors.
3.
It
contains the write enable, read amplifier and
track select circuitry.
4.
It
contains the cartridge interlock circuits.
5.
It contains the solenoid release circuitry.
6.
It
contains a power supply regulator for con-
verting ±24 vdc unregulated voltage into ±15 vdc
regulated voltage.
The Write Head Driver board plugs into the Transport
Electronics board.
RAMP GENERATION
The ramp generator requires four input voltages to
produce four output ramps for RUN FORWARD,
FAST FORWARD, RUN REVERSE and FAST RE-
VERSE speeds. These input voltages are supplied
oy a ,ladder network consisting of IC13 and its re-
lated circuitry. Depending upon whether RUN FOR-
WARD, FAST FORWARD, RUN REVERSE or FAST
REVERSE is selected, a voltage of ±3.5v, ±i3v or
ground will be generated at IC13, pin 6. The output
voltage of IC13, pin 6 is reflected at ICll, pin 6 after
a ramp time.
During
the ramp time, ICIO is com-
pletely saturated, permitting C28 and C29 to charge
to' their respective steady states. The ramp time
can be varied by changing the value of trim resistor
R63.
A higher value of this resistor generates a
faster ramp because it increases the charging current
in R62. Note that the output ramp voltages are neg-
ative for forward motion comlll:ands, positive for re-
verse motion commands.
The output of the ramp generator at Test Point A is
supplied to IC12, pin 3, and to the velocity servo
summing junction through a speed
adjust~ent
poten-
tiometer, R66.
The velocity servo consists of summing network IC12
and related components for tach voltage and input
signal, preamplifier stage Q8, Q9, QlO, Qll with
'its limited gain, and voltage follower type power
amplifier 2N37l4/2N3790 which is mounted on the
motorplate. Tape speed is adjusted by R66 as de-
scribed in paragraph 4.7.2 of the maintenance section.
A AND B HOLES
The output of the MRD 450 photosensors located on
deck are supplied to a pair of operational amplifiers
IC14 and IC15.
The output of these amplifiers is inverted--by IC3 'and
supplied to the interface whenever an A or B hole
is detected.
The A and B indications are used to
locate tape position. Detection of these holes is AC
coupled.
WRITE ENABLE
The Transport Electronics board contains a SAFE
switch which disables tape writing when it is opened.
The switch is controlled by the position of the write
enable plug on the cartridge. When the plug is in the
WRITE position, it closes the SAFE switch in the
file protect assembly, applying +5v write drive volt-
age to the write heads through transistor Q1. When
the write enable plug is in the SAFE position, the 5v
supply is disconnected and a SAFE true signal is
transmitted to the interface through pin W.
CARTRIDGE INTERLOCK
When the cartridge is inserted properly, three inter-
lock switches are closed.
If
the sensor lamp is not
burned out, transistor Q7 turns on, supplying READY
true to the interface at pin P. This enables the tape
motion operation.
.
READ PREAMPLIFIER
The state of SELECT A, SELECT B and the WRITE
ENABLE signals determines whether SDl, SD2, SD3
or SD4 will be-generated to turn on one of the read
heads. When SDI goes true (low), for example, it
triggers the gate of N type FET Q3, passing read
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