I posed this question a few years back with no response, so I am hoping someone else has figured this out in the last few years. I have a shelf in the field (terminating end) and the IMA card that feeds the shelf keeps going into Comm Fail alarm. I have changed out the card several times but it continues to fail. This shelf also has a DS3 card in the self, even though there is no DS3 feeding the shelf. I haven't changed out the PCU yet, but plan to do that next. Any other ideas...