Mitsubishi Electric MDS-B-SPJ2 Series Specification Manual page 170

(9) The motor does not rotate above a certain speed.
Investigation items
1 Check the speed
command. Also check
whether the machine
operation panel
override input is input.
2 Check whether the
load has suddenly
become heavy.
3 Rotate the motor by
hand and check
whether the bearing is
normal.
4 Jiggle the speed
detector connector
(spindle drive unit side
and speed detector
side) to see whether it
is coming loose.
5 Turn the power OFF,
and check the speed
detector cable
connection with a
tester. (Especially
check the shield
wiring.)
11. Troubleshooting
Investigation results
The speed command is not input
correctly.
The speed command is input
correctly.
The load has become heavy.
No particular problem.
The motor does not rotate smoothly.
The motor rotates smoothly.
Connector came (was coming) loose. Install correctly.
Connectors are normal.
The connection is faulty, or there is a
broken wire.
The waveform is normal.
11 − 26
Remedy
Correctly input the speed command.
Investigate item 2, and carry out the
appropriate measures.
Correct the machine side.
Investigate item 3, and carry out the
appropriate measures.
Replace the spindle motor.
Investigate item 4, and carry out the
appropriate measures.
Investigate item 5, and carry out the
appropriate measures.
Replace the detector cable. Correctly
connect the cable.
Replace the spindle drive unit.