09 January, 2016

How to locate the fault point on a fiber optic cable without tools

24 port switch with Allied Telesys Quality

There are expensive cable testing tools that tell us quickly and reliably what fiber cable is failing sending the light signal, but do not usually indicate where it has been broken. 
But with a simple trick we can see which section of the connection is broken , just using a powerful chip CREE LED Flashlight XML-T6 and the ability of the fiber to transmit any light waveform trhough it.
At one end we put the flashlight focusing terminations:

And we can go to the other side to see if the light comes well to the other end. As I found in one of the LC connectors point of light it was significantly weaker than the other:

So I had to test if it was any ST / LC patch cord fiber optic cable made ​​of 3 mm broken, with cover LSZH (Low Smoke Zero Halogen) or fiber connection itself. I plugged in the flashlight in one hand:

And I examined the suspicious cable by removing the protector, where I saw it had a notch where it had bent excessively, partially breaking the fiber. Indeed, I ended braking it totally after bending it a bit again, resulting in the fiber not transmitting light (note the white point of light on the good one):

We were lucky that it is not the main cable; changing the terminal cable with another of 1 mt. long the problem was solved; It must have been some rough handling which damaged the fiber.

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