Mori Seiki SL1H
Yasnac 2000GII

Powered it up one morning and suddenly could not index turret or move tailstock in and out.

Machine was not crashed and was cutting normally previous day.
Hydraulic pressure good.
Hydraulic chuck still worked via foot pedal.
No errors on screen or error LED's on control panel.
Still able to jog axis around and turn spindle on/off.

After playing with controls noticed that rarely I could suddenly get tailstock to work again, but never turret.
Tailstock would then become inoperable again very quickly.
Did not hear any relays or solenoids click when pressing tailstock or turret buttons.

Inspected KRTR relay in electrical cabinet. It was not toggling position when turret index was being commanded.
Its red flag was not visible, indicating it was in the UNCLAMP position.
Command voltages to it (58 and 59) were either idle or UNCLAMP, never CLAMP.
All the above behavior regarding KRTR indicates it was working to UNCLAMP the turret, as it should, yet the turret was NOT unclamping.
Just in case I misinterpreted something, swapped it with another identical relay that was known working (the chuck relay) and no change in behavior.

Voltages from KRTR going to the turret hydraulic solenoid were also in the UNCLAMP state, as they should be, however they were around 90V instead of 100V.

Reconfigured 100V transformer to match intput voltage, now solenoid voltage at 98V. But no change in behavior.

Measured solenoid coil resistances at 26 ohms each side. Same as known working chuck solenoid.

Measured current going into solenoid by manually powering it through ammeter and measured about 300ma each side. Solenoid could now be heard to click for the first time as I powered/unpowered each coil. Yet turret did not visibly unclamp.

Watched hydraulic lines going to turret as I manually operated solenoid valve. They pulsed as they usually do when the pressure changes.

At this point the problem no longer seemed to be electrical or related to the solenoid valve or hydraulics leading up to the turret.

I started tapping the turret with a plastic hammer. No change.

I forced the solenoid into the UNCLAMP position (it may have been in the CLAMP position while I was tapping).

Then I started tapping it again and it suddenly released.

Now everything works.

So the turret was physically stuck for some reason.

I have not disassembled this turret before so I'm not sure how this could occur.

I am not sure how old the oil in the turret transmission is nor if the transmission could even cause the clamp to stick.

I unscrewed the turret drain bolt until it all most came out, and noticed oil starting to weep through, so I know its not bone dry, but I have no idea how much oil is in there (or if it even matters).

The clear oil level window is so old I'm not sure if I'm seeing an oil level or a stain (or if it even matters for this problem).

I do notice sometimes when the turret re-clamps that it makes a somewhat loud CLUNK. I am not that familiar with this machine so I dont know if thats normal or not, but suspect not.

Some internal behavior I noticed:

The reason I could get the tailstock to intermittently work (when the turret was stuck) was because when the turret index knob was set to where the turret was currently indexed, the NC stopped sending out the "TURRET UNCLAMP" (K00 bit 4) signal, and therefore, also I think stopped waiting for the TURRENT UNCLAMP FIN signal (I41 bit 6), and so there was no interlock active and the tailstock was allowed to work. But apparently this "interlock" does not prevent the spindle or hydraulic chuck or possibly other things from working. I did not see this "interlock" constructed in the schematics or wiring diagrams but I could have missed it. They are very old and hard to see. Note this is all just a theory and not 100% certain. Also the specific bit locations are probably not the same if your machine is a different model/control/vintage.

Also