If you are comfortable with Unix, you can log into the console of the PBX (or SSH in) as root and review the logs in the /var/log/asterisk directory. One of the most helpful (and most verbose) is the /var/log/asterisk/full log.
From there, look around the approximate time your trunk goes down and search through looking for the actual event that downed your line. From there, we should be able to get you a more detailed cause.
@lgaetz why did you edit my post? I should have said “Logfiles” and not “Logs” – but not “Info.” The logfiles module will get him the logs in the FreePBX web interface, or at least that’s how it works on mine. Am I missing something?
@billsimon - No, you were right. The logfiles module will let the GUI access the log files, but the limits (500 lines IIRC ???) can be “not deep enough” to get back to a few days ago.
Wasn’t saying you were wrong - just offering another way to get to the information.