PLC 5 - CLX Coversion Problem

Hello Guys,

I have run into a strange problem while doing a PLC-5 to ControLogix conversion.

When I switch out the old PLC-5 processor for a 1771-ASB, my ControLogix PLC can only read and write to the first 8 bits of the discrete I/O modules.

The rack is a 3/4 rack set up for 2-slot addressing, and the ControLogix PLC is scanning through a 1771-DHRIO/E.
I thought at first the problem may be that RSLogix 5000 can only be configured to recognize 177-DHRIO/D cards, but from reading other posts it does not sound like it should be an issue.

If anyone has any ideas as to what the problem may be it would be extremely appreciated!

update: Looking at the backplane switches the PLC-5 uses switch numbers 4 & 5 to configure addressing (both off is 2-slot) while the ASB module uses switch numbers 5 & 6 (again both off is 2-slot). So IF (big if) switch 6 has failed closed it would tell the ASB that it is half-slot addressed. This would explain why the rack works fine with a PLC in the first slot but not with an ASB.

Could this be the problem? Has anyone ever seen one of these dip-switches fail on a rack before?

OK, still fighting this thing. We switched out the rack, same problem. However, we have now found out that everything works as long as there is no card in the last slot of the rack. The last card is an output card (ODD). If anyone has even the slightest idea of what my be happening here I would truly appreciate it. Thanks guys.