sundance-communications.com/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Fiber passes test but wont' work?

Was asked to test and repair some fiber strands that have been in place for quite some time but refuse to work.
I brought our Fluke, it's a bit old and hasn't been calibrated in a while, but it's always done the trick.
First strand passed on the 800nm at 1.6db, second fluctuated between 3.5db and 10db. Figured it was a bad connector at the other end because it dropped to 3.5 as he was disconnecting the patch cord. Replaced it and it passed at 3.5db.
However, the two 10base Fiber transceivers refuse to link. If I set them alternating to Test mode, they link up, but won't in operating mode.
I tested the other two strands and they're also in the same range of 3.5db.

I pulled the transceiver from the first two strands that are working at twice the distance and it still didn't link so I know it's not the units. Those two strands passed at about 3.4db full length.

I replaced several more ends, but no change. I tried testing directly to the fiber terminations, bypassing the patch panel, no change.

The only thing I can think of is that the units are using 1300nm and the two working strands are JUST within spec and pass and work, while the rest are just barely out of spec and won't work.

How can I tell what wavelength the units are operating on? Am I missing something simple???

Stupid question: Do you have the transmit and receive transposed on one end?

You will probably need to go to the manufacture's website for the specs on the transceivers. Which ones are you using and what are the fiber specs? 50 /62.5, length? Do you have access to an OTDR?

No worries on the stupid questions, we don't do much fiber and it pretty much either works or doesn't. However, we have swapped the tx/rx.

I think the fiber is 62.5, length is probably less than 500m.

Don't know what an OTDR is.

Your fibers pass testing. Loopback, not thru patch panel, the new fibers to one transceiver. That should provide a link light. Make sure all patch cords and connectors are the same type as your cable. 50/125 or 62.5/125.

OTDR=optical time-domain reflectometer it would be used to analyze the fiber.

Some transceivers have a thing called link loss carry forward that drops the link on the ethernet side if it sees the link drop on the other side. You might need to test with both ends hooked to a pc or switch.

I agree with all of the above.... I will add that on some Transceivers that the speed of the network switches needs to be hard coded the same. I learned this the hard way. You might try looking at the doc's that came with the transceivers. If you don't find the info you need in there, try there 1-800 number.

OTDR- Optical Time Domain Relflectometer- which is a fiber tester that gives a graphical readout of the loss and at what point in the run the the loss occurs.

Since OTDR's are extremely pricey (I only rent them when necessary), there's still the extremely handy tool called the Visual Fault Finder, made by several companies. (Here's a link: https://cableorganizer.com/fiber-optic-testers/)
If you've got a kink in your link (forgive the rhyme), this usually shows it. About $300.

An OTDR will show you EXACTLY where the fault is, down to the foot. So, if the Plumber decided your Innerduct for that run, was actually a Dryer Hose (and smashed it with his new Drain Pipe), you can find the exact point in the run that Water and Electricity (well, in this case, LIGHT) wouldn't mix.

Ditto on hard-coding the speed on the cheaper Media Converters.

Here is a past thread elating to what I was referencing on hard coding the network speeds.

https://www.sundance-communications.../get_topic/f/24/t/000558/p/1.html#000003

This may or may not be your problem but it sounds as if your ends are OK.