PLC-5 to ControlLogix Migration: A Practical Guide for 2026
June 2026 · 8 min read
If your plant was built before 2005, there's a good chance an Allen-Bradley PLC-5 is still running something critical. The 1785-L60B, L80B, and other PLC-5 processors have proven remarkably durable — many units installed in the 1990s are still operating 24/7 without issues. But with Rockwell Automation having discontinued the PLC-5 platform in 2012, every maintenance manager eventually faces the same question: should we migrate to ControlLogix, or keep running the PLC-5?
The Real Cost of Migration
Migrating from PLC-5 to ControlLogix (1756 series) is not a firmware update — it's a complete hardware replacement. Here's what you're actually looking at:
| Component | Estimated Cost (USD) |
|---|---|
| ControlLogix processor (1756-L8x) | $3,000–$8,000 |
| EtherNet/IP communication module | $1,500–$3,000 |
| 1756 I/O modules (replacing 1771 I/O) | $200–$800 per module |
| Chassis, power supply, wiring conversion | $5,000–$15,000 |
| Engineering labor (80–200 hours) | $12,000–$30,000 |
| Total per PLC-5 rack | $25,000–$60,000+ |
When Migration Makes Sense
- You need Ethernet/IP connectivity and DH+ isn't cutting it anymore for data collection and SCADA integration.
- Your spare parts supply is critically low and you're paying emergency pricing for every replacement 1771 I/O module.
- You're adding significant new I/O and the PLC-5 rack is at capacity with no expansion slots.
- Cybersecurity requirements mandate modern authentication and network segmentation that PLC-5 can't support.
When Keeping the PLC-5 Is the Smarter Move
- The program works perfectly. These ladder logic programs have been debugged over decades. Rewriting introduces risk of logic errors that could cause production issues.
- You have a strategic spare parts inventory. If you've stocked 1785-L60B processors, 1771 I/O modules, and power supplies, you can keep the system running for another decade.
- The system is isolated and doesn't need modern connectivity. Many PLC-5 systems run standalone processes that don't require Ethernet integration.
- Budget constraints make migration impossible in the current fiscal year, and the existing system is reliable.
The Spare Parts Strategy
If you decide to keep your PLC-5 running, here's what you should stock:
- 1× spare processor (1785-L60B, L80B, or your specific model) — tested and with a fresh battery installed
- 1× spare power supply per rack
- 2–3× spare I/O modules of each type in your system (discrete input, discrete output, analog input, analog output)
- 1× spare DH+ communication module if you use DH+ networking
- RSLogix 5 software license and a working programming cable (1784-CP10 or equivalent)
At PLC Parts Direct, we stock all common PLC-5 spare parts — processors, I/O modules, power supplies, chassis, and communication modules. All units are functionally tested with 48-hour burn-in.