Safety Requirements; General Requirements; Access To Pcbs In St750 Cabinet Assembly - Siemens ST750 General Handbook

Note that PCBs are not generally available separately as spares, but are included in
kits. If a PCB fails a new board may be taken from the replacement kit, or the whole
kit may be replaced. See Appendix A for part numbers.

7.4.1 Safety Requirements

Before replacing any fuses, PCBs etc., IT IS ESSENTIAL THAT THE
POWER TO THE ST750 IS ISOLATED. See the Safety Warning on
Warning!
page 2 for details.
Failure to isolate the supply before changing parts may result in
Warning!
damage to the ST750

7.4.2 General Requirements

When replacing PCBs the original PCB should be inspected and the following points
checked:
(a) Check the connectors on the PCB. Are any pins bent, broken or damaged in any
way? If there are, make a note of the PCB and pin number in the Controller Visit
Log Book as the ribbon backplanes may have been damaged.
(b) Check any ICs that are mounted in sockets and ensure that they are the correct
ones for the position and are securely fitted. Refer to the works specification for
further details.
A problem with a loose fitting IC or use of an incorrect one can usually be
rectified easily without having to fit a replacement PCB.
(c) Do not forget to record the replacement in the Controller Visit Log Book.

7.4.3 Access to PCBs in ST750 Cabinet Assembly

The ST750 CPU PCB is mounted directly on the outside of the ST750 Rack
Assembly hinged front plate and is easy to access once the Lid is removed from the
equipment mounting frame.
If a fault is suspected with the Phase Drive PCB, the whole Power/Phase assembly
is replaced as described in section 7.4.6.
If fitted, the I/O Board or OTU Board are fitted inside the ST750 Rack Assembly,
behind the CPU PCB.
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ENERAL ANDBOOK
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