tenance
P44x/EN MT/Hb
P444 (MT) 10-
Without exerting excessive force or damaging the scheme wiring, pull the terminal blocks
away from their internal connectors.
Remove the screws used to fasten the relay to the panel, rack, etc. These are the screws
with the larger diameter heads that are accessible when the access covers are fitted and
open.
If the top and bottom access covers have been removed, do not remove the screws
with the smaller diameter heads that are accessible. These screws hold the front
panel on the relay.
Withdraw the relay from the panel, rack, etc. carefully because it is heavy due to the internal
transformers.
To reinstall the repaired or replacement relay follow the above instructions in reverse,
ensuring that each terminal block is returned to its in the correct position and the case earth,
IRIG-B and fibre optic connections are replaced.
Once reinstallation is complete the relay should be recommissioned using the instructions in
sections 1 to 7 (inclusive) of this chapter.
1.3.2 Replacing a PCB
If the relay fails to operate correctly refer to section P44x/EN TS, ‘Troubleshooting’, to help
determine which PCB is faulty.
To replace any of the relay’s PCBs it is necessary to first remove the front panel.
Before removing the front panel to replace a PCB the auxiliary supply must be
removed. It is also strongly recommended that the voltage and current transformer
connections and trip circuit be isolated.
Open the top and bottom access covers. With size 60TE cases the access covers have two
hinge-assistance T-pieces that clear the front panel moulding when the access covers are
opened by more than 90°, therefore allowing their removal.
If fitted, remove the transparent secondary front cover. A description of how to do this is
given in the Introduction chapter.
By slightly bending the access covers at one end, the end pivot can be removed from its
socket and the access cover removed to give access to the screws that fasten the front
panel to the case.
The size 40TE case has four crosshead screws fastening the front panel to the case, one in
each corner, in recessed holes. The size 60TE case has two additional screws, one midway
along each of the top and bottom edges of the front plate. Undo and remove the screws.
Do not remove the screws with the larger diameter heads that are accessible when the
access covers are fitted and open. These screws hold the relay in its mounting (panel
or cubicle).
When the screws have been removed, the complete front panel can be pulled forward and
separated from the metal case. Caution should be observed at this stage because the front
panel is connected to the rest of the relay circuitry by a 64-way ribbon cable.
Additionally, from here on, the internal circuitry of the relay is exposed and not protected
against electrostatic discharges, dust ingress, etc. Therefore ESD precautions and clean
working conditions should be maintained at all times.
The ribbon cable is fastened to the front panel using an IDC connector; a socket on the cable
itself and a plug with locking latches on the front panel. Gently push the two locking latches
outwards this will eject the connector socket slightly. Remove the socket from the plug to
disconnect the front panel.
To Next Page
Loading...
