Re: OKUMA LT10-M
First thing to check with Manual vs auto or MDI is the input from the switch. Go into Check Data for the I/O and confirm that the switch is in fact functioning. Input will toggle on/off when the button is pushed. Use the Maintenance manual for a guide of where the input is located Probable EC Input? depending on vintage of control you are working with. Another stupid idea is to make sure that you are actually on the + limits. if it's off by .0001 it's not happening. Auto may pull it back to the limit...MDI well that's different unless it's commanded to go to limits as well. It is normally required to be on the + X or Z limit to index.
If I recall correctly, both turrets are driven off of the same drive unit. I'm guessing that the drive is getting low voltage as described or is starting to fail. Have a qualified person check some of the voltages - especially incoming voltage to make sure it's not dropping. Sometimes when the weather gets warm and the AC units start kicking in locally, voltage will drop enough to start affecting the machinery. You should have a multi tap transformer on that machine, so adjustment should be possible if needed.
Experience is what you get just after you needed it.