Troubleshooting/FAQs
Optical link module
72 Operating Instructions, 01/2020, C79000-G8976-C270-06
Error display of the "CH2"/"CH3" LEDs
1. Check whether
– only modules of the same type are connected to each other optically (see "Network
topologies (Page 53)").
– the optical fiber is permitted for the module type being used and does not exceed the
permitted length, refer to the table in the section "Properties and functions (Page 11)".
– the optical channels connected via fiber-optic cables are set to the same mode, see
section "Operator control (hardware) (Page 21)".
– the ends of the fiber-optic cables and the optical transmission and receiving
components are clean.
– the fiber-optic cable connectors are connected completely and correctly
– the requirements were met when connecting and laying the optical bus cables, see
section "Connecting optical cables (Page 51)".
2. Identify the optical receive level, see section "Optical channels (Page 48)":
– Check the fiber-optic cable attenuation with an optical level meter if the level is in the
range "function not guaranteed" or "optical link power margin reduced". If the
attenuation is too high, replace the fiber-optic cable. If the attenuation is within the
valid range, one of the two OLMs of the problem segment is defective. First, replace
the OLM that supplies the transmit signal for the measurement mentioned above. If
the problem remains, replace the other OLM instead. If there is no optical level meter
at hand, you can still get an idea of where the problem lies simply by swapping over
both fiber-optic cables on both OLMs: If the problem moves with the cables, the fiber
is almost certainly faulty, if it does not, the problem is in one of the OLMs.
– If the level is in the "normal operation" range, first check the transmitting OLM, as
described above, and then , if necessary, the receiving OLM.
– If the level of both OLMs of the disturbed fiber-optic cable segment is within the range
“optical link power margin reduced” or “normal operation”, one of the two OLMs of the
disturbed fiber-optic segment is defective. Once again, in this case replace one OLM
of the disturbed fiber-optic segment first. If the problem remains, replace the other
OLM instead.
Level display lit yellow or red
For active interfaces see previous section "Error display of the "CH2"/"CH3" LEDs".
The level display cannot normally be deactivated. If you want to have the (correctly)
displayed red level of an unused optical interface changed to green, a "short circuit" must be
arranged from the transmitter to the receiver of the channel involved using a suitable fiber-
optic cable. At the same time, the monitoring for this channel must be active. This means for
channel 2, the S1 and S2 switches are turned off and for channel 3, the S3 and S4 switches.
The channel display (yellow LED) remains off and the corresponding level LED is green.
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