System 9.115
We had a system upgrade in January of this year from a 4.3 to a 9.115. At first everything was fine. Then our PRI started dropping calls. The end of that was we discovered we had taken a lightening hit and it fried our PRIs. Our carrier fixed (?) the lines and said 'have fun'. The very next week, our lines started dropping again. Not to the extent of before, but three to four calls a day.
When I pull a dignostic on the system or a PRI card diagnostic, it shows nothing.
Any ideas about what could be going on here?

Depends...
Are all of these calls being dropped at one station? Are you using 550.xxxx phones? If you answered yes to both, you may simply have one phone with a failing hook switch and it may have nothing at all to do with your PRI or the lightening hit. It is not uncommon for those hook switches to fail after years of service.

**Copied from Chris_Carlyle**

If it is only doing 3-4 calls a day, isolating the issue is going to be difficult. If it is duplicatable your job is far easier. I would recommend placing outbound calls on each B channel individually to verify that they all operate properly. I would also check the PRI diagnostics to verify that there are no errors on the T1/E1 card. You want to look for framing errors, slips, CRCs, etc. If all of that checks out, the best that I can suggest would be to turn all ISDN diagnostics and freeze the history queue the next time it happens. You will need very detailed info on the call (ext, number dialed, ANI, exact time/date) and submit the freeze logs to your dealer or Inter-Tel Tech Support for review.

Also, you can check SMDR. Records with an * at the end means the other end disconnected.

When you had the upgrade, was the firmware (PN 828.1552) updated on the T1C Card? It should have chip 827.9831 in slot U4 and 827.9832 in slot U5. (I'm just assuming you have a T1C card and not a T1/E1 card due to the age of the system.)

I would get a time and date of each dropped call from your users, also find out if it was inbound, outbound and find out if it's long distance calls...
Let us know what you find.