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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Controller Family | GuardLogix 5570 |
| Standard User Memory | 8 MB |
| Safety Memory | 4 MB |
| I/O Memory | 0.98 MB |
| Safety Partner Required | 1756-L7SP (installs in slot immediately to the right) |
| Nonvolatile Memory | 1 GB SD card (1784-SD1) ships standard; optional 2 GB (1784-SD2) |
| Energy Storage | Capacitor-based ESM (1756-ESMCAP standard) |
| Max Digital I/O | 128,000 |
| Max Analog I/O | 4,000 |
| Current Draw @ 1.2 V DC | 5 mA |
| Current Draw @ 5.1 V DC | 800 mA |
| Power Dissipation | 2.5 W |
| Thermal Dissipation | 8.5 BTU/hr |
| Safety Rating | SIL 3 / PLe (with safety partner) |
| Built-in Port | USB 2.0 (programming only) |
| Slot Width | 2 (primary + partner) |
| Operating Temperature | 0 °C to +60 °C |
4. Product Introduction
The Allen-Bradley 1756-L73S is the primary controller in a GuardLogix 5570 safety system. It provides 8 MB of standard user memory and 4 MB of dedicated safety memory. When paired with the 1756-L7SP safety partner installed in the adjacent slot to the right, the system is certified for SIL 3 and PLe applications.
The controller ships with a 1 GB SD card and uses a capacitor-based energy storage module instead of a traditional battery. It supports both standard and safety tasks in the same project and communicates over EtherNet/IP, ControlNet, DeviceNet, and other ControlLogix networks. The L73S remains a widely used safety controller for integrated standard-plus-safety applications.
1756-L73S
1756-L73S
1756-L73S
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| Safety task will not run / SIL fault | Missing or mismatched safety partner | ✅ High | Verify 1756-L7SP is installed in the slot immediately to the right and firmware matches | Install correct partner; match firmware revisions |
| Controller will not go to Run | Major fault or ESM issue | ✅ High | Check fault log and alphanumeric display | Clear faults; verify ESM is seated and charged |
| Loss of program / tag data | ESM not charged or SD card problem | ✅ High | Confirm ESM type and SD card status | Allow ESM to charge; replace SD card if needed |
| Safety partner communication loss | Partner removed or backplane issue | ✅ High | Check partner status LEDs and connection diagnostics | Reseat partner; verify chassis power |
| USB port not recognized | Driver or cable issue | ❌ Medium | Use proper USB cable; check device manager | Install correct drivers |
| High backplane current | Chassis overload | ❌ Low | Measure total chassis current draw | Redistribute modules or upgrade power supply |
If diagnostics remain unclear, capture the fault log, safety status bits, and partner module status before contacting support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1756-L73S still in production? The GuardLogix 5570 family is mature. New units may still be available through distribution; current new-design focus is the GuardLogix 5580 series. Confirm availability before ordering.
Q: Does the 1756-L73S work alone for safety applications? No. For SIL 3 / PLe applications a matching 1756-L7SP safety partner must be installed in the slot immediately to the right of the primary controller.
Q: How much memory does the 1756-L73S have? 8 MB of standard user memory and 4 MB of safety memory, plus 0.98 MB of I/O memory. A 1 GB SD card ships standard.
Q: Does it use a battery? No. It uses a capacitor-based energy storage module (ESM). The standard removable module is 1756-ESMCAP.
Q: What is the recommended replacement if upgrading? GuardLogix 5580 safety controllers (L8xS series) are the current generation. Project conversion in Studio 5000 is required.
Q: Can the safety partner be installed in any slot? No. The 1756-L7SP must occupy the slot immediately to the right of the 1756-L73S primary controller.
Q: Why is New Surplus sometimes priced lower? These are genuine Allen-Bradley modules from excess inventory or cancelled projects. They are unused and typically supplied with anti-static protection. They are not refurbished unless specifically stated.
