Table of Contents
Advertisement
Overvoltage and Overcurrent Power Off Sequence
Whenever an overvoltage or an overcurrent condition
is
sensed, one of the OV /OC relays (DM 6-0 l 0 or 6-020)
energizes the -4V supply {Kl3), the +6V supply {Kl4),
and the -30V supply (Kl 5). Energizing OV /OC relay
results in de-energizing contactor K3. De-energizing con-
tactor K3 removes power from the logic and memory bulk
supply.
On an abnormal power off, the power check indicator turns
on to indicate a failure. Test points indicate the power
supply that failed. The energized OV/OC relay contacts
hold the relay energized until the check reset switch is
pressed with the on/off switch off.
After an overvoltage, overcurrent, or an undervoltage failure,
the check reset key must be pressed with the power on/off
switch in the off position to de-energize the OV /OC /UV
relay and to allow a power on sequence. See DM 6-0 l 0
for early design power control sequencing or DM 6-020
for redesigned power control sequencing. Power sequencing
failures do not require this action.
Undervoltage Power Off Sequence
Only the -4V and the +6V outputs sense for undervoltage
conditions. If the -4V ax card senses an undervoltage con-
dition, the -4V ax circuit (a separate card) immediately
shorts the +6V regulator via the SCR across the +6V regu-
lator output. This is a +6V simulated overcurrent condi-
tion and the OV/OC/UV relay Kl4 energizes. The Kl4-l
(K14-2 redesign) contacts remove +24V from contactor K3.
Contactor K3, in turn, removes power to the logic and
memory bulk supply. This results in an immediate system
power off.
Because Kl4 OV/OC/UV relay energizes, +24V is present at
test point 13 to indicate a +6V power failure. However, a
+6V overvoltage, a +6V overcurrent, or a -4V undervoltage
could cause the failure condition.
The -30V regulator senses a +6V undervoltage condition.
When the -30V regulator senses a +6V undervoltage condi-
tion, the -30V OV/OC/UV relay (Kl5) energizes. See
DM 6-010 for early design power control sequencing or
DM 6-020 for redesigned power control sequencing.
Contactor K3 then de-energizes causing an immediate
system power off. Test point 14 equals +24V indicating a
-30V overvoltage, a -30V overcurrent, or a +6V under-
voltage condition.
5-8
Thermal Power Off Sequence
A thermal condition causes relay K2 to be de-energized.
The K2-l {K2-3 redesign) contacts tum on the thermal
light to indicate overheating. Power then sequences off
the same as a normal power off sequence by opening the
power on/off switch circuit.
The thermal light and the power check light are on when
the system power off sequence ends. Turning the power
on/ off switch off turns off the power check light. The
thermal light remains on until the over-temperature con-
dition has been corrected and the power on/ off switch has
been-turned off. Power can then be restored to the system
by turning the power on/off switch on.
Emergency Power Off
When you pull the emergency power off switch, system
power drops immediately. However, power is still applied
to the power input terminals and to the input terminals of
Kl, K3, and K9. If the redesigned power control box is
installed (printed circuit relay panel), power is not applied
to the input terminals of K9 after an emergency power off.
Test Points (TPs)
Test points (TPs) are on the power control box. When a
voltage failure occurs, check these TPs inmumerical se-
quence to determine the voltage that failed. TPs 2-9
indicate which regulator voltage failed during power on or
off sequence.
Note: In a normal system power off state, TP2 will read
+24 Vdc. Because of a system power failure (power check),
+24 Vdc measured on TP2 indicates the -4 Vdc failed to
sequence up.
For example, a +6V regulator sequencing failure is indi-
cated if TPs 24 were zero volts and +24V appeared at TPS.
TPs 10-12 indicate an overvoltage condition, or an over-
current condition. TP13 or TP14 indicates an overvoltage
condition, an overcurrent condition, or an undervoltage
condition. For example, an overvoltage/overcurrent failure
in the -4V regulator occurred if +24V appeared at TPl 2.
If TP13 or TP14 indicated +24V {failure condition), you
may have difficulty in determining if an overvoltage, an
overcurrent, or an undervoltage condition caused the
failure. Refer to the MAP charts to help isolate the failure.
Advertisement
Table of Contents
