1746-OW16 Ghost

Can't take credit for this, a friend had seen it. But Rockwell, etc. were all lost.
Relay output card. Large rack. LOTS of outputs. Output would LIGHT but not close the contacts. Replaced the card. ALL GOOD, till a bit later. Now a different output won't work.

Ended up being the P2 power supply. If there are enough outputs on, the rack power supply is OLDER like me, then there's not enough power to pull all the OW relays in. But it WILL light the lights.

welcome to the forum.

i had this happen several years ago.
reseat the plc and all i/o cards several times.
then reseat the power supply connection several times.
do the same for all chassis interconnection cables.

moisture and other contaminates get into the connections and they go bad.
it could be that the p2 power supply is going bad.
use the configuration tool in rslogix to determine the power supply needed.
if i remember correctly, the 1746-p4 power supply is the most powerful one for the slc 500 family. the only drawback is that it is wider than a p2 suppply.
hope this helps,
james