Fiber Optic Cable not working

Basically I am having a problem with a fiber optic cable connecting 2 switches not working, hired a professional to help fix it and in the end it is still not working.

I need someone to look over the details that I am writing here and hopefully help me solve the problem. Or determine if the professional was not competent enough for the job requiring me to find another professional. At the bottom of the post I will write all the specs of my equipment and such.

I take care of a network with a star topology network design. Just over a week ago one of the branches of the fiber network went down. The fiber that went down is a fiber that connects a building to the central fiber hub.

When this branch went down I did all the basic tests that I could think of to troubleshoot the problem. Although I am not a fiber optic technician and don’t have any testing or termination kits. What I did do was I replaced the switches on both ends and replaced the fiber modules on both ends with spare parts. I also checked all the splices in the fiber and made sure all the connectors where ok. Doing all of this did not fix the problem, so to be sure I then re-checked all the spare parts on other fiber cables to make sure the switches and optic modules were in working order and the result was that the parts were good.

This was all I could think of to do that I was able to do myself and based on the results I tentatively concluded that the cable was probably damaged. So at this point I called a fiber optic professional to come and test / repair the cable. The professional spent a day and a half on the cable and was not able to get it working.

In the end this is what they told me. They said that the fiber did not have good light flow so they replaced some of the connectors on the cable at the splices. They told me that once they were finished replacing connectors there was enough light flowing to allow a gigabyte of data flow. But despite this they were unable to get the green light to show up on the 2 switches verifying connectivity.

Since they were unable to get connectivity they began to theorize of what could be the problem. One of their theories was regarding signal loss from splices. The fiber cable in question has 3 splices, and each splice has of course 2 ends connecting together for a total of 6 connectors. Then add that to the cable having 2 connectors on it that plug into a switch at either end, bringing the total number of connectors to 8. They told me that a cable should never have more than 4 dB loss which means 5 connectors because each connector creates a .75 dB loss. With that figure the fiber currently has 6 dB loss.

What is odd to me about this theory is that the cable has been operating perfectly for about 3 years like this. When I told them this they said that perhaps it was on the edge the whole time and for some reason something happened that tipped the scales just enough to break the alleged flaky connection.

They had another theory which is they thought perhaps one of the switch was broken but as I said I replaced the switches, ports, and optical modules already. At this point I am not sure what to do. I could put a new fiber in the ground and redo it all. But this is very time consuming and costly. So I am trying to find out if anyone else has any ideas if even if someone can tell me that the fiber professional was competent and the information was correct. Perhaps I need to hire someone else to come out here and get it working.

Before I posted on this website I spent about a day researching about Fiber optics, cabling and about dBs. But I know that fiber can be complex so I got a little information but it is nowhere near enough to really know what the problem is or if the professional was competent or not.

In my research I found some information that does contradict what they were saying about 4dB loss being the maximum recommended, because it depends on what the minimum transmit power and minimum receive sensitivity of your devises and distance and other factors.

Please keep in mind that this has been working perfectly for 3 years up until 8 days ago.

Specifics

Length of Fiber: 1000 feet

Fiber Type: Multimode 62.5/125 µm

Fiber Modules: Netgear 1000BASE-SX SFP GBIC Module – model # AGM731F

    Output Optical Power (Avg.)   Minimum -9.5    ----   Maximum -3

    Sensitivity (Avg.)            Minimum –N/A   ---   Maximum -17

Switch #1 Netgear L3 Managed Gigabit Switch – Model # GSM7312

Switch #2 Netgear ProSafe 24 Port 10/100 Smart Switch with 2 Gigabit Ports – Model # FS726T

# of Connectors: 8 SC or LC Connectors in the line on each strand.

The professional told me with his testing meeter he had enough light passing for gigabyte of signal.

Do I need to find another professional who is more skilled?
Do I need to bite the bullet and just berry a new cable in the ground?
Do I need to buy new switches?
Etc.

Thanks for your help
Thomas