Allen-Bradley 1756 ControlLogix Modules: AB 1756-A4 Standard Chassis

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Allen-Bradley 1756 ControlLogix platform, developed by Rockwell Automation, is one of the most widely deployed programmable automation controller (PAC) architectures in global heavy industry. Installed across petrochemical refineries, nuclear power generation facilities, offshore oil & gas platforms, pulp and paper mills, and large-scale water treatment plants, the 1756 series functions as the backbone of process control and discrete manufacturing automation. Its modular backplane architecture supports mixed I/O, redundant CPU configurations, and multi-network communication within a single chassis — making it the reference standard for safety-critical and high-availability control environments. The 1756-A4 Standard Chassis is a 4-slot chassis unit that provides the physical backplane infrastructure for mounting and interconnecting ControlLogix modules in compact panel installations.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced in the late 1990s as a successor to the PLC-5 and SLC 500 families, designed to address the growing demand for scalable, networked control systems. The original 1756 chassis and module set established a common backplane standard that has remained backward-compatible across multiple hardware generations.

Q: How are RFQ terms confirmed?
A: Quantity, required condition, documentation needs, destination and sourcing route are confirmed during RFQ review before quotation.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Chassis

• 1756-A4: 4-slot ControlLogix standard chassis, compact panel installations
• 1756-A7: 7-slot standard chassis, mid-size control panel configurations
• 1756-A10: 10-slot standard chassis, high-density I/O rack deployments
• 1756-A13: 13-slot standard chassis, large-scale process control systems
• 1756-A17: 17-slot standard chassis, maximum module density per rack

Controllers (CPU)

• 1756-L71: ControlLogix 5570 controller, 2MB memory, standard process control
• 1756-L73: ControlLogix 5570 controller, 8MB memory, motion and process
• 1756-L83E: ControlLogix 5580 controller, EtherNet/IP, CIP Security enabled
• 1756-L85E: ControlLogix 5580 controller, 40MB memory, high-performance PAC
• 1756-L61: ControlLogix 5560 controller, legacy generation, EOL status

Digital I/O Modules (DI/DO)

• 1756-IB16: 16-point 24VDC digital input module, sink/source compatible
• 1756-OB16E: 16-point 24VDC digital output module, electronically fused
• 1756-IA16: 16-point 120VAC digital input module, isolated inputs
• 1756-OA16: 16-point 120/240VAC digital output module, triac outputs

Analog I/O Modules (AI/AO)

• 1756-IF16: 16-channel analog input module, 4–20mA / 0–10V configurable
• 1756-OF8: 8-channel analog output module, voltage and current output
• 1756-IF8: 8-channel analog input, high-resolution 16-bit conversion

Communication Adapters

• 1756-EN2T: EtherNet/IP communication module, 10/100 Mbps, single port
• 1756-EN2TR: EtherNet/IP module with DLR (Device Level Ring) topology support
• 1756-CN2: ControlNet communication module, coax media interface
• 1756-DNB: DeviceNet scanner module, master node for DeviceNet networks

Power Supplies

• 1756-PA72: 120/240VAC input power supply, 13A backplane output
• 1756-PB72: 18–32VDC input power supply, 13A backplane output
• 1756-PA75R: Redundant-rated 120/240VAC power supply for high-availability systems

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

Rockwell Automation has progressively discontinued earlier 1756 module generations, including the L1x, L4x, L5x, and L6x controller families, along with associated I/O modules and communication adapters. Facilities operating legacy ControlLogix systems — particularly those with 15–25 year installation histories — face a constrained supply chain for direct replacements.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at a proprietary high-speed serial bus protocol. Modules with degraded backplane connectors or corrupted firmware can cause intermittent faults that are difficult to diagnose in the field. DriveKNMS applies a structured test protocol to all 1756 modules prior to shipment:

• Backplane connector inspection and pin integrity verification under magnification
• Functional power-on test in a live 1756 chassis with RSLogix 5000 / Studio 5000 diagnostics
• I/O channel-level verification for all analog and digital modules using calibrated signal sources
• Communication module network enumeration test on isolated EtherNet/IP and ControlNet segments
• Firmware version identification and documentation for CPU modules
• 48-hour burn-in cycle for controllers and power supply modules flagged as high-criticality

Q: How is condition confirmed before quotation?
A: Available condition, photos, test records and documentation are checked according to the requested model and sourcing channel before a formal RFQ response.