Obsolescence guides · SLC 500 processors (1747) catalogue
SLC 500 is discontinued — what are the options?
Allen-Bradley SLC 500 processors (1747) · 1991–2019, discontinued
Where the platform stands
Rockwell Automation ended production of the SLC 500 platform. The 1747 processors and the 1746 I/O that goes with them are no longer manufactured, and there is no new-stock route to a replacement processor from any authorised distributor.
Why spares are hard to find
The SLC 500 installed base is enormous and most of it is still running, because replacing one means rewriting the program and rewiring the panel. That combination — huge demand, zero new supply — is why a 5/05 processor is one of the harder things to find at short notice, and why prices move upward rather than down.
What actually fails first
From what comes through a repair bench on control gear of this age. Worth reading before you buy a replacement — two of these are cheap fixes that get misdiagnosed as a failed module.
Processors of this era keep the program and retentive data in volatile memory backed by a lithium cell. The cell lasts years, not decades — and when it dies the program goes with it on the next power cycle. Many "dead processor" calls are a flat battery and a lost program. Keep a current backup of the program off the machine; it is the cheapest insurance in the panel.
Electrolytics dry out over 15–25 years, especially in warm panels. The supply does not fail cleanly — it sags under load, which presents as random processor faults and I/O dropouts that look like a software problem. If an old rack is behaving strangely, suspect the supply before the program.
Relay outputs are rated in operations, not years. A contact switching an inductive load every few seconds reaches end of life long before the rest of the module. Symptoms are intermittent: the output is commanded and the device sometimes does not move.
The migration route, and what it really costs
The official route is CompactLogix or ControlLogix with Studio 5000, and Rockwell provide conversion tooling that translates the RSLogix 500 program. Be clear-eyed about the cost: the conversion is a starting point, not a finished program, and **the 1746 I/O does not carry over** — different chassis, different wiring. A realistic SLC migration is a panel rebuild with a commissioning window, not a swap. Plan it for a shutdown; never attempt it on a line that is already stopped.
The case for keeping it running
Substitutions we would consider within the family
Each of these has conditions attached — read them. None is a blind swap, and we do not offer substitutions for safety-related functions at all.
| 1747-L541 | 1747-L542 — fits and runs with no changes |
|---|---|
| 1747-L542 | 1747-L543 — fits and runs with no changes |
| 1747-L551 | 1747-L552 — fits and runs with no changes 1747-L553 — fits and runs with no changes |
| 1747-L552 | 1747-L553 — fits and runs with no changes |
Spares worth holding
If you are keeping the platform running, these are the items whose failure stops production — hold them rather than waiting to need them.
All 21 SLC 500 processors (1747) parts we source →
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Forge Horizons is an independent sourcing merchant and not an authorised distributor or agent of Allen-Bradley. This page is general guidance from our own sourcing experience, not engineering advice — confirm anything safety-related with the manufacturer or your integrator.