Mitsubishi MELSEC-Q CPU Last-Time Buy: Spare or Migration?

For a MELSEC-Q installation, a last-time-buy date is not just a procurement reminder. It is a decision point between securing an exact CPU spare and beginning a controlled migration. Mitsubishi Electric’s technical bulletin FA-A-0418-A lists selected Universal model QCPU modules for production discontinuation in October 2026. The bulletin gives an order-acceptance deadline of September 30, 2026, identifies recommended QnUDVCPU and MELSEC iQ-R alternatives, and states that repair support is planned through October 31, 2033.

That window is close enough to require action, but not a reason to buy unidentified stock in a hurry. The correct first step is to separate installed-base evidence, emergency spare coverage, and migration readiness.

Which MELSEC-Q CPUs are affected?

The Mitsubishi notice covers selected Universal model QCPUs, including Q03UDCPU, Q03UDECPU, Q04UDHCPU, Q04UDEHCPU, Q06UDHCPU, Q06UDEHCPU, Q10UDHCPU, Q10UDEHCPU, Q13UDHCPU, Q13UDEHCPU, Q20UDHCPU, Q20UDEHCPU, Q26UDHCPU, and Q26UDEHCPU. The official bulletin should remain the controlling reference for the exact model list and dates.

Mitsubishi publishes the following broad replacement direction:

• Q03UD and Q03UDE families can be reviewed against Q03UDVCPU or R04CPU.
• Q04UDH and Q04UDE families can be reviewed against Q04UDVCPU, with the iQ-R option determined by the application.
• Q06UDH and Q06UDE families can be reviewed against Q06UDVCPU or R08CPU.
• Q10 and Q13 families may lead to Q13UDVCPU or R16CPU decisions.
• Q20 and Q26 families may lead to Q26UDVCPU or R32CPU decisions.

These are manufacturer-recommended comparison paths, not automatic drop-in substitutions. The controller, rack, network, memory, programming tools, remote I/O, motion functions, and machine validation all remain part of the engineering decision.

What the September deadline means for a maintenance team

If a plant still relies on an affected QCPU, there are two legitimate actions. The first is to buy an exact, verified spare before the order window closes. The second is to migrate the application to a newer QCPU or iQ-R platform during a planned outage. Many sites need both: an exact spare to protect the current asset while a migration is engineered and tested separately.

Do not use annual consumption as the only way to calculate the quantity. A single CPU can deserve priority if it is unique to a critical line and has no tested substitute. Conversely, a larger installed population may share one verified spare if the firmware, program, rack arrangement, communications, and recovery process are genuinely common. Record which machines each spare can serve.

Start with a model-level inventory. Capture the complete CPU order number, hardware revision, firmware, memory card or cassette, rack type, power supply, special function modules, network modules, motion or positioning functions, and cabinet location. Also record the programming software version, project backup location, password or access procedure, and the last recovery test date. A CPU on a storeroom shelf is not full coverage if the project cannot be restored.

Do not confuse a faster CPU with a finished migration

The bulletin shows performance improvements in the recommended replacements, including faster instruction processing and changes to memory and communication interfaces. Those improvements are useful, but they can create additional commissioning work. A new CPU may change scan-time margins, memory behavior, diagnostics, Ethernet or serial arrangements, memory-card handling, and the way the existing engineering project is transferred.

Before approving a replacement, compare:

• Program capacity, scan-time margin, data registers, retentive data, and special instructions.
• Rack and power arrangements, base units, extension modules, and physical cabinet space.
• CC-Link, Ethernet, serial, remote I/O, HMI, drive, and supervisory-system connections.
• Motion, positioning, interrupt, high-speed counter, and timing behavior where used.
• Programming software, conversion tools, project backups, passwords, and change-control records.
• Safety functions, machine interlocks, alarm behavior, and the production acceptance test.

Run the comparison on a representative machine, not only on a disconnected controller. The test should include startup, normal sequence operation, alarm handling, communications loss, power recovery, recipe or data retention, and controlled rollback. If the current project contains undocumented workarounds, migration can expose them for the first time.

Build a last-time-buy RFQ that protects the plant

An RFQ for a QCPU spare should state the complete model number, quantity, required condition, destination, urgency, and whether the request is for exact recovery coverage or a replacement study. Add clear photographs of the nameplate, front face, connectors, memory device, rack position, and adjacent modules.

Ask suppliers to distinguish new, surplus, refurbished, repaired, and exchange condition. Request the inspection scope, traceability evidence, warranty boundary, packaging method, and expected dispatch date. For a replacement proposal, request a written compatibility matrix rather than a statement that the unit is “equivalent.” The matrix should identify confirmed matches, engineering assumptions, required software work, wiring changes, and tests still outstanding.

SmartNexMSK’s Mitsubishi Electric automation parts directory can organize brand-specific requests, while the PLCs and controllers category provides the broader sourcing route. These pages do not confirm that a particular QCPU is listed. Exact availability still depends on the verified model, condition, quantity, and delivery requirement.

Frequently asked questions

What is the last order date for the affected MELSEC-Q CPUs?

Mitsubishi Electric’s bulletin states that order acceptance continues until September 30, 2026. Confirm the date and affected model with the official bulletin before issuing a purchase order.

Does production discontinuation stop repair support immediately?

No. The bulletin states that repair support is planned until October 31, 2033. Repair support is not the same as guaranteed stock, immediate turnaround, or a tested substitute.

Is an iQ-R CPU a direct replacement for a QCPU?

No. The iQ-R path requires application, rack, I/O, communication, software, wiring, safety, and commissioning checks. Use the manufacturer’s mapping as the starting point for engineering review.

Should a plant buy an exact QCPU spare or migrate first?

For a critical line, protect recovery with an exact, verified spare while engineering a representative migration. The balance depends on criticality, repair confidence, outage access, and the cost of validation.

What evidence should accompany a QCPU quotation request?

Send the complete model number, revision, quantity, condition requirement, destination, urgency, label and cabinet photos, and any available project, rack, and communication information.

Use the deadline to create evidence, not panic

The September 30 deadline is a useful forcing function. It gives maintenance, controls engineering, and procurement a clear date for deciding which QCPU assets need exact spare protection and which need a migration test. Send the model number, label photographs, quantity, destination, and outage requirement to [email protected] or WhatsApp/Phone +86 18259474341. The right answer may be an exact spare, a repair plan, or a staged replacement review.