If your are seeing smdr then there are usually two things that can be wrong with the port.
1.The settings on word length, stop bits and parity aren't right: baud rate is because you can see the data coming out and from past experience I have seen stop bits and parity be off and you can still see smdr. You could try playing with those settings to (the transfer of the memory may have corrupted the serial port settings; the cards you swapped were the memory and software and the manual recommends saving and reloading the database; I realize that you couldn't in this situation).
2. The recieve leg of this port could be blown. You stated this was a spare CPU card and it is possible that it had a bad port. You can try access the other port.
There is alot more that a trained tech can try and markk and CMDL_GUY are right that it is best to have them look at it. The econimics of the situation usually favor the guy who knows what he is doing. I doubt very seriously that any vendor would guaranty a fix after hearing that a customer swapped out his own cpu and if he's worth his salt a good tech can have you reprogramed one night after hours if it comes down to that.

Kerry

[Linked Image from commsmith.com]