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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Controller Family | ControlLogix 5570 (Logix5572) |
| User Memory | 4 MB |
| I/O Memory | 0.98 MB |
| 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 |
| Total I/O, Max | 128,000 |
| 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 |
| Built-in Port | USB 2.0 (full-speed, programming only) |
| Display | 4-character alphanumeric |
| Operating Temperature | 0 °C to +60 °C |
| Weight (approx.) | 0.25 kg (0.55 lb) |
4. Product Introduction
The Allen-Bradley 1756-L72 is a ControlLogix 5570 controller with 4 MB of user memory and 0.98 MB of I/O memory. It installs in any slot of a 1756 ControlLogix chassis and supports standard Logix programming languages (ladder, function block, structured text, and SFC).
The controller ships with a 1 GB SD card for nonvolatile storage and uses a capacitor-based energy storage module (ESM) instead of a traditional lithium battery. A front USB port provides local programming access, and a 4-character alphanumeric display shows status and diagnostics. The L7x family remains widely installed and is a common upgrade path from earlier L5x/L6x controllers.
- 1756-L72
- 1756-L72
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| Controller will not go to Run | Major fault or energy storage 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 presence/status | Allow ESM to charge; replace SD card if needed |
| USB port not recognized | Driver or cable issue | ✅ Medium | Use proper USB cable; check device manager | Install correct drivers; try different cable |
| High backplane current / overheating | Chassis overload or poor ventilation | ❌ Medium | Measure total chassis current draw | Redistribute modules or improve cooling |
| SD card errors on display | Corrupted or unsupported card | ✅ High | Verify Rockwell-approved SD card (1784-SD1/SD2) | Format or replace with genuine 1784-SD card |
| I/O connections dropping | Network or produced/consumed tag issue | ❌ Low | Monitor connection status in Studio 5000 | Re-establish I/O and produced/consumed tags |
If diagnostics remain unclear, capture the fault log, alphanumeric display codes, and ESM/SD card status before contacting support.
6. Frequently Asked Questions (FAQ)
Q: Is the 1756-L72 still in production? The L7x family is mature. New units may still be available through distribution, but Rockwell’s current focus is the L8x (5580) series. Confirm current availability before ordering.
Q: How much memory does the 1756-L72 have? It provides 4 MB of user (data and logic) memory and 0.98 MB of I/O memory. A 1 GB SD card ships standard for nonvolatile storage.
Q: Does the 1756-L72 use a battery? No. It uses a capacitor-based energy storage module (ESM). The standard removable module is 1756-ESMCAP. Optional variants include ESMNSE (no residual WallClockTime backup) and ESMNRM (non-removable for security).
Q: What is the recommended replacement if upgrading? The ControlLogix 5580 (L8x) series controllers are the current generation. Project conversion in Studio 5000 is required.
Q: Can multiple L72 controllers be placed in one chassis? Yes. ControlLogix supports multiple controllers in the same chassis, limited by power supply capacity and application design.
Q: What programming software is required? Studio 5000 Logix Designer (version compatible with the controller firmware).
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.
