Obsolescence guides · ControlLogix 1756 catalogue
ControlLogix 1756-L6x processors are discontinued
Allen-Bradley ControlLogix 1756 · 1997–present, large installed base
Where the platform stands
The ControlLogix 5560 series — the 1756-L61 through L65 — is discontinued, along with most of the ControlNet bridge modules that went with it. The platform itself continues: 1756 chassis, I/O and the newer L7x and L8x processors are current.
Why spares are hard to find
This is the comfortable case. Because the chassis and I/O are still in production, only the processor and some comms modules need to come from the secondary market — and there is plenty of L6x about, because sites upgrading to L8x release them.
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.
Where the controller stores its program on removable media, the media is a consumable. A spare card, programmed and labelled, belongs in the panel door.
The migration route, and what it really costs
L7x or L8x in the same chassis. This is the easiest migration on this page: the chassis, power supply, I/O and field wiring all stay. The work is re-targeting the controller in Studio 5000, matching firmware revisions, and a download. **It still needs Studio 5000 v20 or later and a tested conversion** — do it as planned work, not during an outage.
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.
| 1756-L61 | 1756-L62 — needs a configuration change in the plc program 1756-L71 — needs program conversion and re-download |
|---|---|
| 1756-L62 | 1756-L63 — needs a configuration change in the plc program |
| 1756-L63 | 1756-L73 — needs program conversion and re-download |
| 1756-L71 | 1756-L72 — needs a configuration change in the plc program |
| 1756-L72 | 1756-L73 — needs a configuration change in the plc program |
| 1756-IB16 | 1756-IB16D — needs a configuration change in the plc program |
| 1756-ENBT | 1756-EN2T — needs a configuration change in the plc program |
| 1756-CNB | 1756-CN2 — needs a configuration change in the plc program |
| 1756-CNBR | 1756-CN2R — needs a configuration change in the plc program |
| 1756-PA72 | 1756-PA75 — 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.
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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.