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Low Voltage AC Supplies
With a normal power off, 40 vac and 12. 6 vac are
present in CPU.
If
these voltages are to be re-
moved without actuating the emergency power off
circuit, CB-1 should be opened.
Power Sequencing Relays
When working with sequencing relays, remember
not to mix the 18v, 24v, and 48v coils. They all fit
in each other's socket. For instance, a 6 point 18v
relay coil will
fit
in a 6 point 24v socket.
Dual or Multi System Emergency Power Off (EPO)
The EPO bypass switch is used to isolate the multi
system EPO capability. The EPO bypass switch
should only be activated when a shared control unit,
channel, storage device, or CPU must be powered
down and removed from the system configuration
while the rest of the system is being used.
In a dual or multi system configuration, if any
'emergency pull' EPO switch is activated, power is
removed from all units. A complete description of
the EPO network for dual or multi systems is
available in the Original Equipment Manufacturer's
Information manual, IBM System/360 Power Control
Interface, GA22-6906.
Dual System Control
The EPO circuits of two systems (sharing a control
unit, channel, or storage device) are interlocked
with the cable connecting the J47 sockets of each
system. To remove any unit from the system
configuration:
126
(3/71>
Model 50 FF.MM
1. Remove power from both systems.
2. Remove the EPO cables connecting shared
units and the PDU which is being isolated (at the
units) and replace them with dummy plugs.
3. Remove the EPO cable from socket J47 of the
PDU which is not being isolated and replace it with a
dummy plug.
4. Power can now be brought up on the remaining
system.
5. When repairs are completed, reestablish a
common E PO network by removing power from all
units, removing the dummy plugs, and reconnecting
the E PO cables.
Multi System Control
The E PO circuits of three or more interconnected
CPUs are interlocked by connecting the J47 cables
from each CPU to the multi-system EPO control box
(IBM Part No. 5271793). To drop power and remove
any unit from the system configuration:
1.
Drop power on the CPU
to
be isolated.
2. Disconnect all isolated CPU to shared-unit
EPO cables. This allows any EPO switch except the
one on the isolated CPU to control the EPO interface
of the remaining units.
3. Activate the bypass switch on the multi-system
EPO control box.
4. Disconnect the EPO cable between the isolated
CPU and the multi-systems EPO control box; and
insert a dummy plug to bypass the isolated CPU.
5. Deactivate the bypass switch immediately, to
restore the interlocked EPO capability to the re-
mainder of the multi-system units.
6. When the isolated CPU is returned to the EPO
network, a similar procedure should be used to
minimize the time that the bypass switch is active.
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