A programmable logic controller (PLC) is the processor that runs the logic of a machine or a process line, reading inputs, executing the program and driving outputs every scan. When the CPU fails or the model is no longer sold, the whole cell stops. MT.parts keeps 350+ PLCs and controller CPUs in stock from the leading industrial brands, including processors the manufacturer has already discontinued.
Where these controllers are used
- Packaging and bottling lines, sequencing fillers, cappers, labelers and case packers.
- Water and wastewater plants, running pump stations, valves and level control.
- Automotive body shops and weld cells, coordinating robots, fixtures and safety interlocks.
- Food and beverage processing, handling batching, CIP cycles and temperature recipes.
- Conveyors and warehouse material handling, with sortation and tracking logic.
- Machine tools and OEM retrofits, where an older CPU still runs a validated program.
How to choose a replacement PLC
Two CPUs from the same family are rarely interchangeable. Check these before ordering:
- Part number first. The exact catalog number and series letter on the module label is the safest match. Search it in our catalog.
- User memory size, for example 512 KB, 1 MB, 2 MB or 5 MB. Our CompactLogix listings are split by memory for that reason.
- Firmware revision, because the project file has to download into the CPU without a forced upgrade of the whole system.
- Backplane and form factor, chassis based versus DIN rail, plus the number of local I/O modules or expansion slots supported.
- Communication ports on board, such as EtherNet/IP, PROFINET, PROFIBUS, Modbus, DeviceNet or serial, so the CPU still talks to the HMIs, drives and remote racks already installed.
- Supply voltage, 24 V DC versus 120/240 V AC, and the matching chassis power supply if the CPU does not have one built in.
If you are unsure which code replaces yours, send us the nameplate data and our team identifies the correct unit.
New, refurbished and obsolete controllers
We supply three conditions, and the condition is always stated on the product page. New units are factory-sealed. Refurbished units are inspected, repaired where needed and functionally tested before shipping. Obsolete and hard-to-find controllers are processors the manufacturer has discontinued, which is often the only way to keep a validated program and an existing panel running without a full migration. Every controller we ship carries a 12-month warranty.
PLC brands and series we stock
- Allen-Bradley: CompactLogix CPU 512 KB, 750 KB, 1 MB, 1.5 MB and 2 MB, CompactLogix 5380 CPU from 0.6 MB to 5 MB, CompactLogix 5480 CPU 20 MB
- ABB: AC500 PLC components, AC500-eCo CPU with Ethernet
- Siemens: programmable controller CPUs and central units, listed individually by catalog number
- Schneider Electric: PLC processors and controller modules, listed individually by reference
- Omron: programmable controller CPU units, listed individually by part number
- Mitsubishi Electric: PLC CPU modules and compact controllers, listed individually by part number
- WAGO: DIN rail programmable controllers, listed individually by part number
Frequently asked questions
What is the difference between a PLC and an I/O module?
The PLC is the CPU: it stores and executes the program, holds the communication ports and keeps the process image. An I/O module has no program of its own, it only converts field signals into data the CPU reads, digital inputs, analog inputs, relay or transistor outputs. A failed input card is replaced with an I/O module; a failed processor is replaced with a PLC.
Can I replace a discontinued PLC with a newer CPU?
Sometimes, but the newer processor usually needs a different firmware revision, newer programming software and often a different chassis or communication card, which means converting the project and revalidating the machine. Replacing with the same discontinued catalog number keeps the program and the panel untouched. We stock obsolete controllers for exactly that reason.
Do refurbished PLCs come with a warranty?
Yes. New, refurbished and obsolete controllers all ship with a 12-month warranty.
How fast can I get a quote?
We reply to quote requests within 24 hours, including part identification when you only have nameplate data.
Do you ship internationally?
Yes. We ship worldwide, including to plants outside the United States.
Can't find your part number?
If the controller you need is not listed, we source it. Send us the manufacturer, part number and quantity, and our team locates the unit, including discontinued models. Request a quote.
