Allen-Bradley 1756 ControlLogix Modules – 1756-PA75K AC Power Supply

Technical Dossier

Product Details And Specifications

Allen-Bradley 1756 ControlLogix Series Technical Notes

The Allen-Bradley 1756 ControlLogix platform 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 infrastructure, the 1756 chassis-based system has served as the backbone of process and discrete manufacturing automation since its commercial introduction in the late 1990s. Its modular backplane architecture, deterministic communication via ControlNet and EtherNet/IP, and redundancy-capable CPU configurations make it the reference standard for safety-critical and high-availability control applications. The 1756-PA75K AC power supply module is a core infrastructure component within this ecosystem, providing 75W of regulated DC bus power to the 1756 chassis from a 85–265V AC input source.

The Evolution of 1756 ControlLogix Architecture

The ControlLogix platform was introduced by Rockwell Automation in 1997 as a successor to the PLC-5 and SLC 500 families, designed to unify discrete, process, motion, and safety control within a single chassis. The original 1756-L1 and 1756-L20 processors established the Logix execution engine and tag-based programming model that persists through current generations.

The architecture has evolved through three identifiable generations. The first generation (1997–2005) established the chassis, backplane, and initial I/O module library. Power supplies in this era included the 1756-PA72 and 1756-PB72, rated at 72W. The second generation (2005–2015) introduced the L6x processor series with expanded memory and integrated motion capabilities, alongside updated power supply modules including the 1756-PA75 and 1756-PB75 with improved thermal management. The third generation (2015–present) introduced the L8x series processors with dual-port EtherNet/IP, CIP Security, and enhanced diagnostics. The 1756-PA75K is the current-generation AC power supply, backward-compatible with all 1756 chassis variants from 4-slot to 17-slot configurations.

Compatibility considerations are critical for maintenance engineers: L1x–L4x processors require Series A/B I/O modules and are incompatible with Series C firmware revisions on certain analog modules. EtherNet/IP adapter modules (1756-ENBT vs. 1756-EN2T vs. 1756-EN3TR) differ in port count, DLR support, and CIP Security capability. Power supplies are chassis-agnostic but must be matched to the available AC or DC plant supply voltage.

1756 ControlLogix Full Catalog & Functionalities (SKU List)

Power Supply Modules

• 1756-PA75K: 75W AC input (85–265V AC) chassis power supply, current-generation K-series
• 1756-PB75K: 75W DC input (18–32V DC) chassis power supply, current-generation K-series
• 1756-PA72: 72W AC input power supply, legacy Series A/B, discontinued
• 1756-PB72: 72W DC input power supply, legacy Series A/B, discontinued

Controller / CPU Modules

• 1756-L85E: ControlLogix 5580 processor, 40MB user memory, dual-port EtherNet/IP, CIP Security
• 1756-L83E: ControlLogix 5580 processor, 20MB user memory, dual-port EtherNet/IP
• 1756-L73: ControlLogix 5570 processor, 8MB user memory, single EtherNet/IP port
• 1756-L71: ControlLogix 5570 processor, 2MB user memory, entry-level 5570 platform
• 1756-L63: ControlLogix 5560 processor, 8MB user memory, legacy generation, RFQ availability review

Digital Input (DI) Modules

• 1756-IB16: 16-point 24V DC sourcing digital input module
• 1756-IB32: 32-point 24V DC sourcing digital input, high-density format
• 1756-IA16I: 16-point 120V AC isolated digital input module

Digital Output (DO) Modules

• 1756-OB16E: 16-point 24V DC electronically fused sourcing digital output
• 1756-OA16: 16-point 120/240V AC digital output module
• 1756-OB32: 32-point 24V DC sourcing digital output, high-density

Analog Input (AI) Modules

• 1756-IF16: 16-channel single-ended analog input, ±10V / 0–20mA configurable
• 1756-IF8: 8-channel differential analog input, high-resolution 16-bit

Analog Output (AO) Modules

• 1756-OF8: 8-channel analog output, voltage and current configurable per channel

Communication & Network Adapter Modules

• 1756-EN2T: Single-port EtherNet/IP communication module, 100Mbps
• 1756-EN3TR: Dual-port EtherNet/IP with Device Level Ring (DLR) support
• 1756-CN2R: Dual-port ControlNet communication module with redundant media
• 1756-DNB: DeviceNet scanner module for legacy field device integration

Sourcing Hard-to-Find & Obsolete 1756 ControlLogix Parts

A significant portion of installed 1756 ControlLogix systems worldwide operate on hardware that Rockwell Automation has placed on the Product Discontinuation (PD) or End of Life (EOL) list. Modules such as the 1756-PA72, 1756-L63, 1756-DNB, and early-series I/O modules (Series A) are no longer manufactured but remain in active service at facilities where full system migration is not operationally or economically viable.

Quality Control for the 1756 ControlLogix Range

The 1756 backplane operates at a proprietary high-speed serial bus that requires functional validation beyond simple visual inspection. DriveKNMS applies a structured test protocol to all 1756 modules prior to dispatch:

• Power supply modules (including 1756-PA75K) are bench-tested under rated load conditions, with output voltage regulation, ripple, and overcurrent protection verified against Rockwell Automation published specifications.
• CPU modules are powered in a live 1756 chassis, firmware version confirmed, and basic ladder/function block execution validated via RSLogix 5000 / Studio 5000 diagnostic routines.
• Digital I/O modules are point-tested across all channels using a dedicated I/O exerciser fixture, confirming channel isolation and response time within specification.
• Analog modules undergo calibration verification using traceable reference instruments, with channel offset and gain error recorded and compared to factory tolerance bands.
• Communication modules are tested for network enumeration, data table read/write, and connection establishment on live EtherNet/IP and ControlNet test networks.
• All modules are inspected for backplane connector pin integrity, capacitor condition, and conformal coating status before packaging.