Help with HP Switches and Optic Fiber

We have a fibre optic link between two levels of our building.  A few weeks back, the connection between the levels failed early in the morning.  I was the only person here, and know that there was nobody else in the building when it failed.

We immediately had a technician come in to test the fibre, which was OK.  We tried changing switches to no avail, spoke to HP who thought it may be a faulty transceiver, they sent out a replacement which didn't fix them problem.

The original configuration was, Upper level fibre was plugged into a HP Procurve 2650 (J4899B) with a Gigabit Transceiver (J4858B), the fibre end on the lower level was plugged into a HP Procurve 2324 (J4818A) with a Gigabit SX Transceiver (J4131B).

We have a second switch on the lower level, a HP Procurve 2142 (J4868A) with a 100FXSC Transceiver (J4853A) we plugged the fibre into that.  A link light on this switch illuminated, however there was no link light on the switch upstairs.

We moved the J4858B Transceiver to a HP 2824 (J4903A) upstairs, and had exactly the same results, link light was on downstairs, nothing upstairs.  Spoke to HP who thought the J4858B was faulty, sent a J4858C replacement.  I upgraded the firmware on the HP 2824 to cope, plugged in the new transceiver, and had exactly the same problem.  No link light upstairs, link light downstairs, no data being transmitted.

I've ensured the TX and RX cables are plugged into the right spots, even tried switching them around.

We had a second company come in to test the fibre link yesterday, they again confirmed that the fibre cable is functioning properly, and their equipment can send and receive data.  They too could not work out why our equipment could not communicate with each other, given we've tried every possible of switches, transceivers, and fibre cores.

No now I turn to the experts.  Please help!  We're currently "functioning" via a long Cat 6 cable running through the fire escape.  Doesn't look good.

Thanks in Advance.
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Fiber plugged directly into the modules? Or are there fiber patch cables involved?

If there are patch cables, did the fiber techs test the patch cables?
If not... is it possible there is an intermitent connection on the link that is out? Possibly damaged at one end of the run or the other?

One other dumb question the module is MM. Does your fiber match the modules that you are using?

Can you move the switches close together and use a short fiber patch cable to test? If they work on the short cable its the fiber. If they don't it is one of the switches and or modules.

Do you have one running in full-duplex and one running in half duplex mode?

EBASupportAuthor Commented:
Turned out to be one of the Transceivers.  In my ignorance I failed to realise that I could not replace an SX tranceiver with an SC tranceiver, hence why the connection would not establish when trying these different parts.

Ended up calling HP and had them send one of every component until we got it working again.

Thanks for your input.
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