label all line and extension cables on 3rd and 4th 206 cards,turn off power,unplug labeled cables,remove 3rd 206 card and replace with 4th 206 card ,then install 308card last postion and plug all labeled cables back in,power up and test.All settings and extensions should remain same.Do you have backup and restore card on system?If not when was last time batteries were replaced on ACS?I should have mentioned backup and batteries before saying power down system.