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3. Key Technical Specifications
| Parameter | Value |
|---|---|
| Outputs per Module | 16 non-isolated |
| Output Voltage Range | 10 to 60 V DC |
| Nominal On-State Voltage | 48 V DC |
| Continuous Current per Output | 2 A resistive (0.2 A pilot duty) |
| Continuous Current per Module | 8 A maximum |
| Surge Current | 4 A per output for 10 ms (every 2 s) |
| Minimum Load Current | 2.5 mA |
| On-State Voltage Drop | 1.5 V DC maximum |
| Off-State Leakage Current | 0.5 mA maximum |
| Output Signal Delay | Off-to-On 0.1 ms; On-to-Off 0.2 ms |
| Backplane Current | 400 mA @ 5 V DC |
| Power Dissipation | 15.6 W maximum |
| Thermal Dissipation | 53.3 BTU/hr maximum |
| Isolation | 60 V continuous (tested 1000 V AC) |
| Field Wiring Arm | 1771-WH (WHF / WHFB fused options) |
| Keying Bands | 10–12 and 22–24 |
| Compatible Chassis | 1771-A1B through 1771-A4B (not 1771-A4) |
4. Product Introduction
The Allen-Bradley 1771-OBD is a 16-point DC sourcing digital output module for the PLC-5 and 1771 I/O chassis family. It switches 10–60 V DC field power to loads such as solenoids, motor starters, indicators, and relays, with a continuous rating of 2 A per point (8 A total module limit).
It draws 400 mA from the backplane, includes status LEDs and a fuse-blown indicator, and uses the 1771-WH wiring arm for quick module swaps without rewiring. Direct drop-in replacement for existing 1771-OBD modules in local or remote 1771 chassis. Standard choice for brownfield PLC-5 systems that still drive higher-voltage DC loads.
1771-OBD
1771-OBD
5. Troubleshooting Quick Reference
| Symptom | Possible Cause | Relevance to this Part | Quick Check Method | Recommendation |
|---|---|---|---|---|
| No green ACTIVE LED | Chassis 5 V missing or module not seated | ❌ Low | Measure 5 V at backplane; reseat module | Verify chassis power supply before replacing module |
| Fuse-blown LED on | Overloaded output or shorted load | ✅ High | Check field wiring for shorts; measure load current | Replace fuse only after clearing the fault |
| Output LED on but no voltage at terminal | Blown fuse, open load, or failed output circuit | ✅ High | Measure voltage at terminal vs. field common | If LED on and fuse good but no voltage, channel failed |
| Output LED off while PLC bit is on | Addressing error or module not scanned | ✅ Medium | Confirm slot addressing and I/O image map | Check keying bands and processor configuration |
| Output works but trips under load | Exceeding 2 A/point or 8 A module limit | ✅ High | Calculate total load current; check derating curve | Reduce load or add external contactors |
| Intermittent outputs | Loose wiring arm, dirty edge connectors, or marginal supply | ✅ Medium | Inspect connectors and field supply voltage under load | Clean contacts; confirm field supply stays in range |
If these checks do not isolate the fault, provide photos of the module face, wiring arm, fuse status, and a diagnostic buffer capture. Contact technical support with the series letter and any observed error codes.
6. Frequently Asked Questions (FAQ)
Q: Is the 1771-OBD still manufactured? No. The PLC-5 / 1771 platform is discontinued. Available units are New Surplus or fully tested refurbished stock. Confirm current availability and series letter before ordering.
Q: Can I hot-swap the 1771-OBD? No. Power down the chassis before removing or inserting the module. Hot-swapping can damage the backplane and cause unpredictable output states.
Q: What wiring arm is required? 1771-WH is the standard arm. Fused versions 1771-WHF (3 A) and 1771-WHFB (1.5 A) are also compatible. Keep the original arm so field wires stay connected during a swap.
Q: Can a 1771-OB or 1771-OBN replace this module? No. The 1771-OB is only 8 points and limited to 10–27 V. The 1771-OBN is 32 points with different current ratings and keying. Use another 1771-OBD for a direct replacement.
Q: Does the module store any configuration? No. Addressing is set by the chassis keying bands and the processor’s I/O configuration. Always photograph the keying bands (10–12 and 22–24) before removal.
Q: Why is the price lower than a factory-new module? Because production has ended. Units sold as New Surplus or tested refurbished are verified on a live 1771 chassis and carry a 1-year warranty. New production units no longer exist.
Q: What is the maximum continuous current I can draw? 2 A per output and 8 A total for the entire module. Exceeding either limit will blow the fuse or damage the output transistors. Always leave margin and follow the published derating curve for higher ambient temperatures.
