How to source discontinued and obsolete PLC parts

How to find a discontinued PLC part

To source a discontinued PLC part, copy the full catalog or order number from the nameplate, along with the series letter and firmware revision. Check that number's lifecycle status with the manufacturer. Then send all of it, with quantity and a nameplate photo, in one quote request so we can match the exact unit.

The series and firmware decide whether the replacement drops straight in or costs you a shift of reflashing and reconfiguring. If the line has years left in it, plan spares now and price a migration next to them.

Read the nameplate for catalog number, series and firmware

The catalog number identifies a product. The series letter and firmware revision identify the exact unit you're replacing, and a mismatch on either one is what stalls a startup.

Allen-Bradley

Allen-Bradley labels carry the catalog number, such as 1756-L61 or 1756-ENBT, plus a series letter printed as SER A, SER B and so on. Many modules also show a firmware revision, often marked FRN. Write down all three exactly as printed.

The label shows the firmware the module shipped with. If anyone has flashed it since, the running revision will differ, so go online and read it from the module properties in your programming software. The running revision is the one your project depends on.

Siemens

Siemens prints the full article number, also known as the order number or MLFB, along with a product version and a firmware version such as V3.3. Copy every character. Two S7-300 CPU 315-2 DP units can carry different order numbers, 6ES7315-2AG10-0AB0 and 6ES7315-2AH14-0AB0, because they're different hardware generations with different memory.

Your STEP 7 or TIA Portal hardware configuration stores the exact order number and firmware version for each module. That's a better record than a faded label, so pull it from the project if you can.

Other brands

Schneider Electric, Omron and Mitsubishi parts follow the same rule, as do the rest of the automation brands we supply. Send the complete part number with every suffix, plus any hardware or software version on the label. If the label is worn, a clear photo of the module face and side label often settles it.

Why series and firmware decide a drop-in replacement

A module with the right catalog number and the wrong series or firmware can still keep a controller out of Run. On Logix systems it shows up in two places.

Controller firmware has to match the project

A ControlLogix or CompactLogix controller only accepts a download from a project at the same major firmware revision. A replacement at revision 20 won't take a revision 16 project until you flash it with ControlFLASH or convert the project.

That only works inside the range the hardware supports. A later series can need a higher minimum firmware than your project uses, and older controllers have a ceiling. Each major revision also needs a matching version of the programming software, so check what's installed on the plant laptop.

Electronic keying checks I/O and comm modules

Logix I/O configurations set electronic keying for each module, usually Exact Match or Compatible Module. With Exact Match, a module whose major or minor revision differs from the configuration won't connect. Compatible Module generally accepts a later revision, but check the setting in your project before you count on it.

Siemens hardware configuration

On S7 systems, a module with a different order number means editing the hardware configuration and downloading it again. Siemens CPUs generally accept a configuration written for an earlier firmware version, but confirm it in that module's manual before shutdown day.

Check the manufacturer's lifecycle status first

Before you chase a part, look up where it sits in the manufacturer's lifecycle. The status tells you whether the factory still builds it, how long the ordering window lasts and what the manufacturer names as the successor.

Rockwell Automation's Product Lifecycle Status search takes a catalog number and returns one of four statuses for Allen-Bradley hardware:

• Active: the most current offering in its category.
• Active Mature: fully supported, though a newer product or family exists.
• End of Life: a discontinued date is announced, and the part is generally orderable until that date.
• Discontinued: no longer manufactured, though Rockwell notes that repair or exchange services and limited regional stock may still be available.

Siemens uses numbered milestones. Its phase-out notice for S7-300 and ET 200M components set the PM400 phase-out announcement for October 1, 2023 and PM410 product cancellation for October 1, 2025. After PM410 those components are sold only as spare parts, in spare-part quantities, and Siemens says they can no longer cover plant expansions. It doesn't plan PM490 discontinuation until at least ten years after PM400, though it won't guarantee that for every module.

Treat End of Life or PM400 as your last-time-buy window. The part is still orderable from the manufacturer, and you can plan a migration on your own schedule.

What to send when you request a quote

The more of this you send up front, the fewer questions come back before pricing.

From the part itself

• The full catalog or order number, every suffix included.
• The series letter or product version.
• The firmware revision on the label and, if you have it, the revision it's running.
• A photo of the nameplate.

About the order

• Quantity, with spares listed separately from the immediate replacement.
• Whether your team can flash firmware on site before install.
• Any later series or successor part you've already confirmed will work.
• Your needed-by date and ship-to address.

The flashing question widens the search. If you can update firmware on site, a unit at a different revision becomes a workable match. Most of this applies to any equipment order, and our guide on what to include in a quote request covers the rest.

Our team sends back pricing and stock status for each line. In-stock items ship the same or next business day to businesses anywhere in the US.

Plan spares for legacy lines before you need them

Spares planning starts with a list of the installed base. Record every module's catalog number, series and running firmware, rack by rack, and mark the ones that stop the line if they fail.

Controllers, communication modules, power supplies and any specialty card with no in-house substitute come first. A sensible starting point is one spare of each critical module type on site, more if several racks share it.

A spare only helps if it works on the day. Power it up on a bench, flash it to your plant's firmware revision and tag it with the series and revision. Keep the matching project backup and firmware file with it.

Keep watching lifecycle status on every critical part. When one moves to End of Life or PM400, buy the spares you'll need for the rest of the line's planned life.

Stock the small items too. S7-300 CPUs from the Micro Memory Card generation won't run without a SIMATIC MMC, and older Allen-Bradley processors rely on a backup battery to hold the program. Both are cheap and easy to overlook.

When migrating to a current platform makes more sense

Sometimes a spare is the wrong purchase. Migration is usually the better spend when:

• The line needs expansion, which a PM410 or Discontinued part can't support.
• The programming software only runs on an old, unsupported laptop.
• The manufacturer no longer offers repair or exchange for the part.
• A long search for one module would cost more downtime than a planned cutover.

Spares buy time. They don't keep a discontinued part available forever, and the remaining stock gets thinner every year. We can't promise any discontinued part will still be out there next year.

Manufacturers name successors for most legacy lines. Siemens points S7-300 factory automation users to S7-1500 with ET 200MP I/O, and Allen-Bradley's current ControlLogix and CompactLogix families cover most Logix replacements. A migration usually brings a newer network too, so budget for managed industrial Ethernet switches alongside the controller.

We quote PLCs, I/O modules and drives for either route, whether you're stocking spares or moving to a current platform.

Send us the nameplate and we'll quote it

Got a faulted module and a photo of its label? That's enough to start. Send us a quote request with the catalog number, series letter, firmware revision and quantity, and tell us whether you can flash firmware on site.

If you're weighing spares against a migration and want to talk through the part list first, get in touch with our team.

Frequently asked questions

Can a different series letter replace my Allen-Bradley module?

Often, but check before you install it. A later series can need a higher minimum firmware than your project uses, and Exact Match electronic keying rejects a module at a different revision. Read the module's release notes, check the keying setting in your project and confirm your team can flash firmware on site.

How do I find out if a PLC part is discontinued?

Search the catalog or order number in the manufacturer's lifecycle tool. Rockwell Automation's Product Lifecycle Status search returns Active, Active Mature, End of Life or Discontinued for Allen-Bradley parts. Siemens publishes phase-out notices that give PM400, PM410 and PM490 milestone dates for a product family, along with its named successor products.

Does Henry AV list prices for discontinued PLC parts?

No. Henry AV is quote-based and doesn't publish prices online. Send the full catalog number, series, firmware revision and quantity in a quote request, and Henry AV responds with a written quote. Stocked parts ship to businesses nationwide, usually the same or next business day.

How many spares should I keep for a legacy PLC system?

Start with one spare of each critical module type: controllers, communication modules, power supplies and any specialty card with no substitute. Add more when several racks share the part or the manufacturer announces End of Life. Bench-test each spare and flash it to your plant firmware before it goes on the shelf.