Mitsubishi Electric MELSERVO-J4 Series Transition Handbook page 283

Part 6: Review on Replacement of MR-J3-_T_(DIO command/ Serial communication operation) with MR-J4-_A_-RJ
(2) MR-J3-_T_ (Serial communication operation)
Simultaneous replacement with MR-J4-_A_-RJ and an HG motor
Although heavier burdens including a longer construction period
need to be borne, once replaced the system can be operated for a
long period of time. (Refer to Section 2.2 (1).)
Note. Separate repair means replacement.
Controller
HF-_P/HC-_P/HA-_P motor
YES
Servo amplifier and Servo motor
Simultaneous replacement?
MR-J3-_T_
NO
Separate repair of a servo amplifier is available. (Note)
For the available servo motors, refer to
"Part 7: Common Reference Material".
6 - 4
RS-422 communication