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1.
~he
Stop FF (Figure 3-3) is cleared. It
was set previously by dc power up,a Set
Standby State
a:maand,
or
by
a
preriaJs
pres-
sil¥J
(to
extiD;uish)
to STARr
switch/iD:iicatar.
2.
~he
logic provides
an
enable (Figure
3-3)
to energize MOtor relay Kl.
3.
~he
closed contacts of K3 cause the fol-
lowing:
a. +20 volts enables solid state switches
AlQ2, AlQ3, and Q1Q4.
~hese
switches
can now conduct ac
power
to the spin-
dle motor.
b.
Because the motor is stopped, the
centrifugal switch inside the motor
is closed.
~his
provides a ground
enable to AlQ4 to connect the start
winding and capacitor to ac power.
At 2000 rpm the switch transfers to
open, disconnecting- the start winding
and enabling the
run
winding.
c. Apply
GND
to the first seek interlock
motor.
~he
first seek interlock
switch transfers to the not complete
(in progress) position.
d. Removes power from the hysteresis
brake.
4. When the logic determines that the spin-
dle speed exceeds 3000 rpm and the first
seek interlock delay is complete, relay
K2 energizes.
S. With relay
K2
closed
a. +20 vdc distributed to the read/write
logic
b. Retract relay K5 energized (Figure
3-4).
6. The transferring contacts of KS cause
the following:
a. Disconnects the emergency retract
capacitor from the voice coil while
connecting it to the -16v power sup-
ply to allow it to charge to -16
volts.
b. Connects the power amplifier A2Al
to the pOSitioner so that the logic
may control the positioner.
7. The first seek interlock switch mechan-
ically transfers to the complete posi-
tion upon completion of the interlock
motor revolution (15 seconds for first
seek delay).
This removes the remaining
ground to the interlock motor to disable
it.
It also signals load heads to the
logic.
3-8
8. Completion of the first seek delay al-
lows the start of the First Seek (load
heads) function.
The logic commands the
posi tioner to move the carriage forward.
Refer to the Pirst Seek discussion for
further informatione
9.
When the heads move into the pack,
the
heads loaded switch closes.
This causes
the following:
.
a. Provides a control signal to thelo;L:
for further loading/unloading sequenc-
ing.
b.
Maintains a motor relay
K3
enable so
that the motor continues to operate
if the control interlock opens.
This
prevents the motor from being shut
down until the heads are unloaded.
c. Energizes relay K6.
If any condition
occurs where Retract relay KS opens,
K6
continues to apply -16v retract
voltage to the voice coil until the
heads unload.
d. Enables the -16v Sense circuit.
If
the -16v power becomes insuffiCient
(loss of power), fault is set and
Retract relay K5 opens.
Relay K5
connects the retract voltage to the
voice coil while removing logic con-
trol of
the
voice coil.
EMERGENCY RETRACT AND
DATA
PROTECTION
Certain emergency conditions could occur
which require immediate disabling of the
write circuits and full retraction of the
heads.
These conditions are:
1. Loss of ac power, either site power
or UNIT POWER circuit breaker.
2. Opening of any of the control inter-
locks (Figure 3-4).
3.
OVerheating of spindle motor,
If this
occurs, the spindle motor thermostat
(Figure 3-3) opens:
this applies ac
across the DRIVE MOTOR circuit breaker
coil to open the contacts.
Loss of
speed (step
4)
occurs.
4.
Loss of spindle motor speed.
S. Loss of
any
of the following ac voltages:
+20Y, ±9.7, or -16.
If any of these conditions occur, the read/
write logic is disabled and the heads are
unloaded.
Refer to Figure 3-5 for
t~ng
of
these conditions.
83318200
A
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