Siemens SIMATIC S7-400 Hardware And Installation Manual page 174

Maintenance
Warning
!
Improper handling of the front connectors can result in injury and damage.
If the front connector is removed and inserted during operation, hazardous
voltages of >25 VAC or >60 VDC may be present at the pins of the module.
When such voltages are present at the front connector, modules with power
applied may only be replaced by electrical specialists or trained personnel in such
a way that the pins of the module are not touched.
To change the fuses, follow the steps outlined below:
1. You must have taken the appropriate action in your STEP 7 program to ensure
correct responses from your system.
If you are not sure whether your program will react correctly, set the CPU mode
switch to STOP.
2. Loosen the mounting screw of the front connector and pull it off.
3. Loosen the mounting screws of the module.
4. Swing the module out.
Note
In order that the removal and insertion of digital modules can be detected by the
CPU, a minimum time of two seconds must elapse between removal and
insertion.
5. Remove the covers on the right-hand side of the module by levering them out
with a screwdriver.
6. Replace the defective fuses with new fuses of the same type.
7. Place the guides on the covers into the appropriate cutouts in the module
casing and close the covers until they click into place.
8. Attach the module onto its slot and swing it down.
9. Screw the module on with both mounting screws.
10.Fit the front connector.
11. If you have switched the CPU to STOP, you must now switch it to RUN again.
12.After fitting, each programmable module will be reinitialized by the CPU with
parameters.
How the S7-400 Behaves after Replacing the Fuse
If an error occurs after replacing a fuse, you can read out the cause of the error
from the diagnostic buffer.
7-10
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S7-400 and M7-400 Programmable Controllers, Installation Manual
C79000-G7076-C424-01