Instructions to recover from a failed Finisar connection

We had two different failure modes that cause an alarm in the finisar connection:

1. Problem in the Front End Electronics
2. Problem in the Read Out Module

Please note that Finisar is a company that produced the optical electronics used to connect the front end electronics with the read out modules. Depending on the documentation, you might find the names Finisar, optical fibre link, G-Link, or D-Link used for the same thing.

Checks before doing any further tests

In order to have a G-Link connection, the front end and the ROMs have to be switched on. If the front end is off, you will see another alarm in the DIRC WCR or DIRC FEE section. If this is the case, solve that problem first.

Also, the ROMs have to be switched on. Go to the electronics hut rack 27 and check that the ROMs are switched on.

For any problem with the ROM, please page ODF.

Finding out where the problem is

An easy way of finding out whether the problem originates at the ROMs or at the Front End Electronics is to swap the fibre showing the error with a fibre that does not show an error.

Check the error lights at the ROMs to see which fibre is causing the trouble.

1. Unplug the fibres. Currently, the whole assembly is a bit fragile, be carefull that the connector does not fall apart. Make sure to remember which fibre is the upper fibre.
2. Unplug a second, working fibre. Plug this into the location of the original fibre. Plug the first fibre into the other location.
3. Check the error lights. Only one connection should be in error mode.
4. Swap the fibres back to the original place.
5. In case the same error light was still on, continue with Fixing a problem in the Read Out Modules below. If the problem moved, continue with Fixing a problem in the Front End Electronics.

Fixing a problem in the Front End Electronics

Information on the nominal values of variables monitoring the finisar and the optical link can be found here.

To fix alarms, try to power-cycle the corresponding Wiener crate.
If this does not help, it might be a broken chip in the DCC in the magnetic shielding. To fix this, it would require to open the backward doors. Contact the DIRC experts and the run coordinator.
If data taking is ongoing, make sure that one cannot take data in the current configuration before requesting an immediate opening of the backward doors: the problem may not be on the FINISAR itself but rather on the DCC canbus line. In that case, monitoring information will be wrong but the dataflow is likely to be OK!

Fixing a problem in the Read Out Modules

If you have a problem with the ROMs, page ODF. In general, they would like to have a look before any other fixes are tried.

In case of urgency or if you can not reach ODF, you can try to reboot the ROMs as described here. If this does not fix the problem, wait for the ODF crew.