I have an 200 EL LW 19. I have one SS420 that goes into NO SYNC (lights flashing as if it was resetting). I changed phones, no good. Changed DNIC, good for a couple days, then same issue again. Changed SS420 again and it's good for the time being.

I don't believe I have a BCCIII, but not 100% sure.

What could be the problem. Should I replace the BCC?

This is the only phone doing this. I have about 12-15 dnic ports in use.

I would check the wiring/jack first then BCC

The cause is the DNIC cards. They need to a minimum revision of 4.6 for the White DNIC and at least 2.5 for the Blue DNIC. Older revisions do not have a fuse that can cause the card to overheat, which in turn can lead to system resets. The error log shows up as "excessive messaging. set removed from service" I've had this occur on several older EL systems. Once the newer style card was installed, haven't had an issue since.

thanks, the wiring is in good shape.

So far so good. But I will check the card.

Does the user wear a wired headset? Is there a source of static, such as new carpeting?

I have had static from plugging in and unplugging headsets cause erratic dead phones. Users with static resistant mats tend to get it less. Also, users who will touch metal on their desks before connecting are less likely to get this sort of problem.

That would be my next thing to check.