Loss Of Ac Power 3-D; Control Interlock Opening 3-!J; Loss Of Speed; Loss Of Dc Power - Honeywell BR3C9 Operation Manual

LOSS OF AC POWER
The following events occur upon catastrophic
loss of the ac power or opening of either
Sv circuit breaker.
1. All dc power supplies ~ their outputs
to zero and the logic is disabled.
2. All relays open.
3. With KS open,
the
normally-closed con-
tacts of KS (Figure 3-4) provide a path
from the emergency retract capacitor
A2C2 to the voice coil. This negative
voltage pulls the carriage back to its
retracted stop.
4. With K2 open, +20 vdc is removed from
the read/write logic.
I
When power is restored, drives without the
power sequence feature and drives with this
featu~e
and in local mode are restarted by
press1ng the START switch. Drives with the
power sequence feature and in remote mode
automatically restart when power is resto;ed.
CONTROL INTERLOCK OPENING
If the control interlock (Figure 3-4) opens,
the heads unload normally as explained in
Power Off Sequence. Pressing START to ex-
tinguish the indicator opens the interlock
to initiate the normal unload heads sequence.
There are certain special emergency sensing
conditions:
1. If either the +10 or -10 circuit breaker
opens, AlQl (Figure 3-2) is disabled.
The effect is the same as if all ac
power were lost. All ac power input to
the dc power supplies is opened except
to +20Y.
2. Opening a 20v circuit breaker generates
an undervoltage condition to light the
CHECK indicator.
3. Opening of any other circuit breaker or
interlock breaks the control interlock.
All of these conditions extinguish the START
indicator and unload the heads. Any under-
voltage condition (±20v or ±Sv) sets the Pack
Unsafe FF and lights the CHECK indicator.
lOSS OF SPEED
If the spindle motor speed drops below 2700
rpm, the following events occur:
1. The speed detection circuit in the logic
detects the speed loss and opens Speed
relay K2. As a backup circuit, when
the speed is less than about 2000 rpm,
the motor centrifugal switch closes.
This breaks the gate in the -16v sense
circuit (Figure 3-4) to open KS and
enerqizes K4 to start a new first seek
interlock time delay.
83318200 E
2. With x2 open:
a. KS opens to apply -16v retract vol-
taqe to the voice coil.
b. +20 vdc power is removed from the
read/write logic.
3. Relay X3 is de-energized when speed
drops below 2700 rpm.
4. Relay K6 remains energized to continue
to apply -16v retract voltage until the
heads retract sufficiently to open the
heads loaded switch.
LOSS OF DC POWER
If +20Y power is lost, all relays open and
the ac input to the dc power supplies is
opened. The effect is the same as if all.ac
power were lost.
If +9.7v is insufficient, the following occur:
1. Relays K2 and K3 are opened by the +Sv
Sense circuit.
2. With K2 open:
a. KS opens to apply -16v retract power.
b. +20v power removed from read/write
chassis. With the heads still load-
ed, the write circuit generates a
Current Fault.
3. With K3 open:
a. The spindle motor is disabled.
b. The hysteresis brake is enerqized.
4. In addition the undervoltage condition
will liqhtothe CHECK indicator and raise
DSB2 bit 2. The condition must be
cleared to load heads aqain.
If -16v power is lost, the following occur:
1. The -16v Sense circuit opens KS. It
also generates an undervoltage fault
condition to set the PACK UNSAFE FF
and open One Start Interlock (Figure
3-3).
2. With KS open, retract power is applied
to the voice coil. Since the undervol-
taqe fault has disabled the read/write
logic, the circuit is disabled prior to
carriage retraction.
3. Relay KS remains energized, so the drive
motor continues to run. Heads cannot
load until the CHECK indicator is
cl~.
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