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CHAPTER 5: Troubleshooting
fiberoptic cable or one of the multiplexors. First, check the muxes’ switch
settings and their RS-232 connectors. If these are OK, check the fiberoptic
cable’s connectors and the muxes’ optical transmitters and receivers for
fingerprints and other things that could impede or distort optical signals. If
you find anything, clean the affected surface with an alcohol-saturated cotton
swab. If you can’t remove the offending substance, call us for technical
support. After cleaning, try your data communication again. If data still can’t
get through, proceed with the fiberoptic testing that the rest of this section is
concerned with.
If you have an optical power meter, you can pinpoint the problem quickly.
Disconnect the cables from the muxes’ transmitters and test the data signals
as they emerge directly from the transmitters. If a signal is weak or dead when
it is output, the transmitter is faulty. If both signals are strong at that point,
reconnect the the cables and test the signals as they emerge from the other
ends of the cables. If a signal that is output strongly is weak or dead at the
receiver end of the cable, the cable is faulty. If both signals are strong at the
receiver ends of the cables, one of the receivers is probably faulty. Replace
faulty cables; send muxes with faulty transmitters or receivers back to us for
repair (see
Section 5.7
).
If an optical power meter isn’t available, these steps will at least help you to
narrow the possibilities:
1. If both muxes pass the local loop test (see
Section 5.3.3
), go to Step 3. If
both muxes fail the local loop test, proceed to Step 2 and check both
transmitters. If only one of the muxes fails, proceed to Step 2 and check
its transmitter. If you can’t do the local loop test, check the SDCD LEDs
on both multiplexors. If this LED is OFF on one of the muxes, proceed to
Step 2 and check the transmitter on the opposite mux; if the SDCD LED
is OFF on both muxes, go to Step 4.
2. To check an optical transmitter’s LED, unscrew or untwist the cable
connector attached to the mux’s TX connector, turn off or dim the lights
in the room, and hold a thin sheet of white paper in front of the optical
transmitter. A faint red glow should be visible on the paper, since the
transmitter LED puts out a small amount of visible red light in addition to
its primarily infrared output. If no glow can be seen, even with the room
in total darkness, the transmitter isn’t working; see
Section 5.7
for
instructions on shipping the mux for repair.
