The way to find this is by using TRACE.
Trace can find intermittent issues by constant recording of any desired signal every 8 milliseconds.
Then viewing the Y-output to X-input time variance and comparing the failure event to a series of non-failures
I have attached a presentation of TRACE, for what I believe your control to be, as well as the most current Fanuc control (in case someone else needs the info.)
Use your electrical manual to decide which signals are monitored in the SAMPLING ADDRESSES
Use the alarm number as the "STOP TRIGGER" for the trace.
If monitoring over a LOOONNGG time, use SIGNAL TRANSITION as the trace format.
If monitoring just tool changes...real quick...change...change...change..., then use TIME CYCLE
Last hint: Arrange your signals in a "CAUSE AND EFFECT" format
Tool change cause and effect flow for a CAM style arm:
1. M6 is given.
1a. (ladder) Does X=Y (if the tool being call=the tool in the spindle...do nothing)
2. (motion) Move to second reference
3. (I/O) send tool binary information to Servo for magazine = Y-out in binary format followed by START command
4. (I/O) X-in verifies position in binary followed by a VPF (verify position flag)
4a. (ladder) Does X=Y (if not=alarm)
6. (motion) Spindle orient
7. (I/O) Y-out = Pot down
7a. (I/O) X-in = pot NOT up
7b. ...time
7c. X-in = pot down
8. (I/O) Y-out = Changer arm motor FWD
8a. (I/O) X-in = Changer Arm Home Position NOT (CAHP.M turns to 0)
8b. CAM rotation occurs up to 2 degrees before arm grabs tools
8b1. (I/O) X-in SX (switch/proximity) for unclamp is seen
8b1a.(I/O) Y-out is sent for unclamp cylinder solenoid
8b1a1. (I/O) X-in for cylinder clamped (actually better name would be cylinder NOT UNCLAMPING) turns off
8b1a2. ...time
8b1a3. cylinder easily crosses airspace to touch the PUSHER to the top of the DRAWBAR
8b1a4. Cylinder lifts to cross airspace between bottom FLANGE of cylinder and STOP RING of spindle
8b1a5. Cylinder exerts real pressure to compress Belleville Washers, moving the drawbar to the clear area in the spindle core that lets the collet open
8b1a6. (I/O) X-in for cylinder unclamped is seen
8b2. ...tools swap places (Rotation and axial movement combined)
8b3. (I/O) X-in SX (switch/proximity) for clamp is seen
8b3a (I/O) Y-out is cancelled for unclamp cylinder solenoid
...with no hydraulic (or possibly pneumatic) pressure the Belleville Washers fling the unclamp piston upward
8b3a1. (I/O) X-in for cylinder unclamped is removed
...the cylinder does apply Hyd/Pneu to cause the piston to lift, but the bellville's are the real force. piston lifts pusher across airspace and sets the flange back down
8b3a2. (I/O) X-in for cylinder clamped (actually better name would be cylinder NOT UNCLAMPING) turns on
8c. ...arm continues through rotation
8c1. On SOME machines: an "approach" proximity switch is seen, causing the motor to reduce the CAM's speed
8c2. CAHP.M is seen
8c3. (I/O) Y-out = Changer arm motor FWD is turned off
9. (I/O) Y-out = Pot down
9a. (I/O) X-in = pot NOT down
9b. ...time
9c. X-in = pot up
10. M6=finished