Allen-Bradley 1747-L551 SLC 500 Processor – Pickup in Store
In stock: 8 units in Milwaukee, WI. Physically stocked and ready to ship or available for local pickup. Includes a 1-year full-function warranty.
SLC 5/05 PLC Processor · 16K Words User Memory · channel 0 RS-232 (DF1 / DH-485 / ASCII) and channel 1 Ethernet (10Base-T; 10/100 on later series)
Actual NJT inventory photos
| Part Number | 1747-L551 |
| Description | SLC 5/05 PLC Processor. In stock in used and refurbished condition, Series C and D. |
| Shipping | Ships same or next business day
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| Pickup | Free local pickup at 2122 N Prospect Ave. Call ahead at (414) 331-5954. |
| Warranty | 1-year full-function warranty provided by NJT Automation. Warranty details
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| Returns | 90-day free returns. View return policy |
| Exchange | Send us your defective 1747-L551 after your purchase for a 10% core credit. We also purchase old or damaged parts outright. |
Replacement Options for 1747-L551
| Variants | Part NumberConditionSeriesQtyPrice 1747-L551 /C$1,129.99 Used · Series C · 1 in stock1747-L551 /CUsedSeries C1$1,129.99 USD 1747-L551 /C$1,199.99 Used · Series C · 1 in stock1747-L551 /CUsedSeries C1$1,199.99 USD 1747-L551 /C$1,349.99 Refurbished · Series C · 4 in stock1747-L551 /CRefurbishedSeries C4$1,349.99 USD 1747-L551 /C$1,419.99 Refurbished · Series C · 1 in stock1747-L551 /CRefurbishedSeries C1$1,419.99 USD 1747-L551 /D$1,999.99 Used · Series D · 1 in stock1747-L551 /DUsedSeries D1$1,999.99 USD | ||||||||||||||||||||||||||
| Availability | 8 units in stock | ||||||||||||||||||||||||||
| Repairs | 1747-L551 Mail-In Repair Service | Flat RateFlat rate: $949.99 | ||||||||||||||||||||||||||
Part Number Decoder | SLC 5/05 PLC Processor 1747L551
Decoded from the Rockwell Automation catalog-number structure. Series and firmware revision are printed on the product label, not encoded here. | ||||||||||||||||||||||||||
Series & Revisions | Series C and D in stock; other series on request. Series A shipped with OS500 and can be flashed to OS501; Series B and C ship with OS501. Only Series C hardware has the 10/100 Mbps Ethernet port; A and B run 10 Mbps half duplex. Series notes: Same slot and wiring. A later series runs an earlier program; an earlier series rejects a program that uses newer OS/FRN features. | ||||||||||||||||||||||||||
Intended Use | Designed for Ethernet-connected legacy machine and small-process control applications. SLC 500 processors still run packaging lines, conveyors, water and wastewater stations, HVAC plants and OEM machinery installed through the 1990s and 2000s. Most demand today is replacing a failed processor like-for-like so the existing rack, I/O and RSLogix 500 program stay in place. | ||||||||||||||||||||||||||
Migration Path | Rockwell Automation has discontinued SLC 500 processors; replacement units come from the surplus market. Published successor for the SLC 500 modular processor: CompactLogix 5380 (5069-L3xxER) with Compact 5000 I/O, or CompactLogix 5370 (1769-L3xER) to reuse 1769 Compact I/O.
A like-for-like replacement or a repair keeps the existing program, wiring and panel layout; a migration is a project. Both are listed on this page so the choice can be made on lead time and budget. | ||||||||||||||||||||||||||
Physical Data | Weight and DimensionsEst. weight0.82 lb (0.37 kg)H × W × D5.7 × 1.4 × 5.7 in. (145 × 35 × 145 mm)
Product dimensions are typical manufacturer-published values and may differ by series or option. Unit weight is an estimate; no published figure is available for this catalog number. Shipping box and weight are estimates for freight planning; the packed unit may ship in a different box. | ||||||||||||||||||||||||||
Similar Part Numbers | |||||||||||||||||||||||||||
Allen Bradley Information | Technical Specifications12 parameters from manufacturer-published specifications
Typical manufacturer-published values for this catalog number; confirm against the current manufacturer documentation before specifying. | ||||||||||||||||||||||||||
| Category | SLC 500 | ||||||||||||||||||||||||||
| UPC / GTIN | 10662072745622 | ||||||||||||||||||||||||||
| Part Number | 1747-L551 | ||||||||||||||||||||||||||
| Manufacturer | Allen-Bradley | ||||||||||||||||||||||||||
Previously sold 1747-L5517 sold · +5 on eBay
NJT Automation has supplied and shipped 7 1747-L551 SLC 5/05 PLC Processors since 2024; these listings are sold and the in-stock options above are ready to ship.
- Sold
- 7 since 2024
- Series
- A × 3, B × 2, C × 2
Image gallery106 PHOTOSActual units photographed by NJT
Can the 1747-L551 be repaired?
Yes. NJT Automation repairs the 1747-L551 by mail-in: diagnostic evaluation, component-level repair and a functional test, backed by a 1-year full-function warranty.
Option 1
NJT managed repair
- Evaluation
- Free. No repair, no charge.
- Shipping
- Prepaid UPS label both ways.
- Pricing
- $650 minimum. Rush service available.
- Warranty
- 1-year full-function warranty included; 2- and 3-year options.
Option 2
Independent repair bids. Compare quotes from independent repair technicians. Post your repair on RepairMode to receive competitive bids from experienced technicians. Each technician sets their own pricing and warranty.
Common Failures
Failure patterns we regularly see on SLC 5/05 PLC Processor hardware like the 1747-L551:
- FLT LED on and the processor will not go to RUN (major fault that returns after clearing)
- DH+ channel 1 dead on a 5/04 (transceiver failure on the 3-pin blue-hose port)
- Keyswitch worn: processor will not stay in RUN or REM
- Program lost on power cycle: BATT LED on, battery (1747-BA) depleted
- Channel 0 RS-232 port damaged by a hot-plugged or miswired programming cable
Fault code reference
1747-L551 Fault Codes
50 codes · 1747-RM001
Fault codes a SLC 5/05 PLC Processor reports on status word S:6 in RSLogix 500 (hexadecimal), as documented in Rockwell Automation publication 1747-RM001. Use them to narrow a problem down to the unit, its wiring or the application before sending it in for repair.
| Code | Fault | What it indicates |
|---|---|---|
| 0001 | NVRAM error | Processor memory was corrupted: noise, lightning, poor grounding or missing surge suppression on inductive loads. The default program is loaded. |
| 0002 | Unexpected hardware watchdog timeout | The processor reset unexpectedly; usually electrical noise or a failing processor. |
| 0003 | Memory module memory error | The memory module is corrupted. This can also occur when going to REM Run mode. |
| 0004 | Memory error in Run mode | Processor memory became corrupt while running. |
| 0007 | Memory module transfer failure | Transfer from the memory module failed; the module is corrupted. |
| 0008 | Internal software error | Unexpected software error, typically caused by noise or a hardware problem. |
| 0009 | Internal hardware error | Unexpected hardware error inside the processor. |
| 0010 | Processor revision too low | The processor does not meet the revision level the program requires. |
| 0011 | Program file 2 absent | Executable program file number 2 is missing: incompatible or corrupt program. |
| 0012 | Ladder program memory error | The ladder program has a memory integrity problem. |
Show 40 more codes
| 0013 | Memory module absent | The required memory module is absent, or S:1/10 / S:1/11 is not set as the program requires. |
| 0014 | Internal file error | Processor data files are corrupted. |
| 0015 | Configuration file error | The I/O configuration file is corrupted. |
| 0016 | Startup protection after power loss | S:1/9 is set and power was lost while running; the processor waits for the fault routine to clear it. |
| 0017 | NVRAM / memory module mismatch | S:2/9 is set and the memory module program does not match the NVRAM program. |
| 0018 | Incompatible user program | Operating system type mismatch: the program was written for a different or newer processor. |
| 0019 | Duplicate label | A duplicate or missing LBL instruction was found in a subroutine. |
| 001F | Online edit integrity problem | Noise, communication loss or a power cycle occurred during an online editing session. |
| 0020 | Minor error at end of scan | A minor error bit in S:5 (lower byte) was set at the end of the scan, for example a math overflow. |
| 0021 | Remote expansion chassis power failure | An expansion I/O chassis lost power, or an over-voltage / over-current condition occurred. |
| 0022 | Watchdog scan time exceeded | The program scan took longer than the watchdog setpoint, or the program is caught in a loop. |
| 0023 | Invalid STI interrupt file | The STI interrupt file number is invalid or the subroutine does not exist. |
| 0024 | Invalid STI interval | The STI setpoint is greater than 2550 ms or negative. |
| 0025–0027 | Excessive stack depth / JSR calls | A JSR instruction is calling the STI, I/O interrupt or user fault routine file directly. |
| 0028 | Invalid startup-protection fault routine | The fault routine file number in the status file does not exist or is invalid. |
| 0029–002D | Indexed / indirect address error | An indexed or indirect address references outside its data file or data space. |
| 002E | Invalid DII input slot | The DII slot is empty or does not hold a discrete input module. |
| 002F | Invalid DII interrupt file | The DII interrupt file number is invalid or the subroutine does not exist. |
| 0030 | Subroutine nesting exceeded | Too many nested JSRs, or potentially recursive routines. |
| 0031 | Unsupported instruction | The processor type or series does not support an instruction in the program. |
| 0032 | Sequencer out of range | A sequencer length / position parameter points past the end of a data file. |
| 0033 | Bit shift / FIFO / LIFO out of range | The length parameter of an LFU, LFL, FFU, FFL, BSL or BSR instruction points past the end of a data file. |
| 0034 | Negative timer value | A negative timer accumulator or preset value was detected. |
| 0035 | TND / SVC / REF in interrupt routine | A TND, SVC or REF instruction is used inside an interrupt or user fault routine. |
| 0036 | Invalid PID parameter | An invalid value is being used for a PID instruction parameter. |
| 0038 | RET outside subroutine | A RET instruction resides in the main program file. |
| 003A | Write to protected file | An attempt was made to write to a constant / protected data file. |
| 003B | Firmware mismatch | Motherboard and daughter card firmware were not flash-upgraded as a pair. |
| 003C | STI watchdog timeout | The STI setpoint is set too low for the routine. |
| 005F | Invalid rack ID | Invalid rack setup or a problem with the rack. |
| xx50 | Chassis data error | Slot xx returned bad chassis data; usually noise or grounding. |
| xx51 | Stuck runtime error | A stuck I/O module in slot xx: noise on a discrete module or a fault on a specialty module. |
| xx52 | Module missing | The module configured for slot xx is missing or was removed. |
| xx53 | Unused slot has module | A slot declared unused contains a module, or a module reset itself. |
| xx54 | Wrong module type | The module in slot xx is a different type than configured. |
| xx55 | Wrong I/O count | The discrete module in slot xx has a different I/O count than configured. |
| xx56 | Chassis configuration error | The chassis configuration in the program does not match the hardware. |
| xx57–xx5E | Specialty module error | A specialty I/O module in slot xx faulted, timed out or has an invalid G / M0-M1 file configuration. |
| xx90–xx93 | Disabled-slot / ISR error | A specialty module in a disabled slot requested service or faulted, or its interrupt subroutine is invalid. |
| xx94 | Module inserted under power | A module was inserted under power in Run or Test mode, or reset itself. |
Where the manual's only remedy for a code is to replace the unit or module, the code is pointing at a hardware fault inside that part. Those are the faults NJT Automation repairs at component level, so a repair quote is usually the first thing to check before buying a replacement.
Source: Rockwell Automation publication 1747-RM001, SLC 500 Instruction Set Reference Manual. Codes are listed as documented; fault behaviour can vary by firmware revision, so confirm against the manual for your unit's series.
Photos by NJT Automation; test videos from NJT or network repair technicians.
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