DL2 IRIS SHUT..NEED HELP??

We have (4) DL2's on a downstage truss and one of them over the last month on and off has its iris shut and we cant get it open. Any ideas...its probley something really dumb that we are missing...We have tried to powercycle & home all..still we cannot get this iris to open on the one unit!!! Dmx is responding as to the movement and we can see the bulb lite inside. Any ideas? Thanks....Dale