[nznog] Juniper console ports

Just a quick question to those using juniper MX series routers.. or perhaps any series - is there a known issue with the console port dying ? We've seen this happen on two different boxes - completely unresponsive after running for a few weeks, reboot doesn't fix it, and no output at all on it, even during the freebsd boot sequence. So before I start second and third-guessing what I've been doing to it, is this a known issue that people have seen elsewhere ?