ST750
G
ENERAL
H
ANDBOOK
667/HB/33750/000
Page 102
Issue 6
Warning
To open the hinged plate, the 64-way Phase Control Ribbon cables at
the front of the ST750 Rack Assembly must be disconnected.
Disconnection of the cable disconnects all logic power from the CPU
and therefore prevents the ST750 operating the lights,
but it does not
switch the incoming mains off
. The mains
must
be isolated at the
master switch before any disconnection of cables or fuse replacement
takes place.
7.4.4 Access to PCBs in other Outercases
All ST75
0 Rack Assemblies installed in cabinets with 19” mounting kits provide full
access to the front face of the ST750 and have sufficient room to allow the hinged
front plate to swing open, giving access to the internal PCBs.
Access to the PCBs is the same as described in section 7.4.3.
7.4.5 Replacement of CPU PCB
Ensure that the replacement PCB has the correct firmwares fitted and they are of
the correct variant and issue. Refer to the Works Order Specification for details.
The mounting pillars on the CPU are a nylon clip type and only require the clipping
mechanism to be released to allow the board to be removed. The pillars are retained
on the hinge plate by means of an integral clipping mechanism on the other end.
When the CPU is replaced, make sure that the clipping mechanism of the mounting
pillar is fully engaged.
Warning
Care must be exercised when removing or inserting the green connectors
and their cables from the PCB, as strong extraction and insertion forces are
required. Be careful not to over flex the board, which could cause tracks to fracture
and the board to fail.
7.4.6 Replacement of Power/Phase Assembly
The Power/Phase assembly may be removed once the following have been carried
out:
•
Isolate the Mains to the ST750 at the master switch
Important
See notes on CPU compatibility between ST750 and ST700
contained in section 2.1.7
Warning!
On
NO ACCOUNT
is it permitted to downgrade an ST750 site to
an ST700 site by changing the CPU board and associated
firmware as an ST750 site will conform to TR2500A which the
ST700
DOES NOT and CAN NOT