MR-J3-BS to MR-J4-B replacement requires checking and remapping the CN8 safety-signal positions against the exact manuals; the two series do not use the same STO signal layout. The decisive migration check is the signal-to-terminal mapping at CN8, not the connector name alone.
CN8 signal layout decides whether the existing safety wiring transfers
MR-J3 safety amplifiers marked with the BS suffix provide an STO input at CN8. Standard MR-J3 amplifiers do not have this input. On MR-J3-BS, the CN8 signal arrangement differs from the MR-J4-B arrangement, so an existing harness or terminal-by-terminal connection cannot be assumed to transfer directly during replacement.
STO is a safety function that prevents the drive from producing torque when its safety input is activated. It does not itself disconnect mains power or make the motor or machine safe to work on. Treat CN8 as safety-circuit wiring: preserve the safety function by wiring according to the destination amplifier's documentation and validating the complete safety circuit after the change.
| Check | What the evidence establishes | Where to decide or verify |
|---|---|---|
| Source amplifier | MR-J3-*BS variants have STO at CN8; standard MR-J3 models do not. | Read the complete amplifier model marking. |
| Signal positions | CN8 signal arrangement differs between MR-J3 safety and MR-J4-B. | Compare the CN8 wiring diagrams in the manuals for the exact models. |
| Replacement wiring | Connector identity does not establish equivalent terminal assignments. | Trace each safety-circuit conductor to its signal and destination terminal. |
Model identification separates safety and standard MR-J3 units
Confirm that the removed amplifier is an MR-J3 safety model before evaluating CN8 wiring. The listed affected models are:
MR-J3-10BS, MR-J3-20BS, MR-J3-40BS, MR-J3-60BS, MR-J3-70BS, MR-J3-100BS, MR-J3-200BS, MR-J3-350BS, MR-J3-500BS, MR-J3-700BS, MR-J3-11KBS, MR-J3-15KBS, MR-J3-22KBS, MR-J3-10BS1, MR-J3-20BS1, and MR-J3-40BS1.
Use the full model number, including suffixes, to locate the applicable diagrams. The warning concerns MR-J3 safety amplifiers and replacement by an MR-J4-B; it does not establish CN8 terminal assignments for every variant. Confirm both the source and destination model documentation before changing conductors.
Manual comparison is the supported migration approach
Two practical approaches are available: carry the existing CN8 conductor positions across unchanged, or compare signal functions and rewire to the MR-J4-B assignments. Because the signal layouts differ, the first approach offers no assurance of functional equivalence. The manual-based comparison is the recommended path.
| Approach | Decision criterion | Result |
|---|---|---|
| Reuse existing CN8 positions | Assumes matching terminal assignments. | Not a valid assumption for this migration; the layouts differ. |
| Map signals using both manuals | Matches each circuit function to the destination terminal. | Use this approach before reconnecting or commissioning. |
The manuals supplied for this migration are SH030084 and SH030106. Locate the CN8 safety-input diagrams applicable to the exact amplifier models. Do not infer pin numbers from connector appearance or from another MR-J3/MR-J4 variant.
Signal-by-signal remapping keeps CN8 functions aligned
- Record the complete model number of the removed MR-J3-BS and the installed MR-J4-B.
- Identify every conductor connected to CN8 and document its current terminal and safety-circuit function before disconnection.
- Use the manuals' applicable CN8 diagrams to compare the MR-J3 safety and MR-J4-B signal arrangements. Build a conductor-to-function-to-destination-terminal map; use the documented labels and assignments rather than wire color or physical position alone.
- Reconnect conductors to the destination terminals specified for those functions. If any circuit function or terminal assignment cannot be matched unambiguously, stop before energizing and resolve the mapping with the exact model documentation or Mitsubishi support.
- Inspect the completed connections against the map and the destination diagram before testing.
This procedure does not provide pin numbers because the source material does not reproduce the diagrams. The manuals' model-specific CN8 assignments govern; a guessed pinout would undermine the safety circuit.
Safety-function testing confirms the remap
After wiring, verify the safety circuit using the machine's approved commissioning and validation process. Confirm that the safety input responds as intended, that the drive enters the expected STO condition when the safety function is demanded, and that normal operation is permitted only after the safety circuit returns to its valid state. Check the actual drive indication and safety-circuit behavior against the MR-J4-B manual and the machine's safety design.
A logic or wiring error can prevent the intended safety response even when the connector is fully seated. If the drive behavior differs from the documented response, isolate the machine according to site procedures, recheck conductor mapping and terminal seating, and repeat validation before returning the axis to service. Keep the completed mapping and test results with the machine's electrical documentation.
FAQ: MR-J3-BS to MR-J4-B CN8 migration
How do I wire MR-J3-BS CN8 to an MR-J4-B?
Compare the CN8 diagrams for the exact source and destination models, then map each conductor by safety-circuit function to the MR-J4-B terminal assignment. The two series have different signal layouts, so do not transfer connections by position alone.
How do I know if my MR-J3 has STO at CN8?
Check the amplifier's full model marking. MR-J3 models with the BS safety designation have CN8 STO; standard MR-J3 amplifiers do not.
How do I find the correct MR-J4-B CN8 pinout?
Use the CN8 safety-input diagram in the manual applicable to the exact MR-J4-B model. The supplied manuals are SH030084 and SH030106.
Can I reuse the MR-J3-BS CN8 wiring positions unchanged?
No. The MR-J3 safety and MR-J4-B signal arrangements differ. Match circuit functions to the destination diagram before reconnecting.
How do I verify STO after replacing an MR-J3-BS?
Run the machine's approved safety commissioning test and confirm the drive responds as documented when STO is demanded and released. Stop and escalate to Mitsubishi support if the model-specific assignment is unclear or the validated safety response is not achieved.