There are several fixes for those I units, hence all the mod # on them. They do predate become a tech just like Dave mentioned. There are probably ASC updates on them, and I may have one or two, but not sure where. Those fixes are typically about signal strength, I also believe there was a jumper depending on which memory chip it got.
Bruce, have you gone through the TIU trouble shooting in your manual, there are voltage checks on the Receiver board you can do. G