Allen-Bradley · ControlLogix
1756-L71 Repair
Allen-Bradley ControlLogix L71 processor (1756-L71). Test-and-verify service with an honest verdict — plus repair of the supplies and modules around it.
Known failures on the 1756-L71
- ▸SD/firmware faults
- ▸Backplane wear
Ship your unit to
USPS
Control Board Lab
PO Box 120241
Arlington, TX 76012
UPS / FedEx
Control Board Lab
1009 Oakwood Ln # 120241
Arlington, TX 76012
Write your RMA number on the outside of the box and include it on a note inside. Units over 50 lb (large VFDs, spindle drives, industrial PCs in enclosures) ship by freight — contact us before ordering and we will arrange dock-to-dock shipping.
Check these before you ship
Some of these will tell you the 1756-L71 is fine and the fault is elsewhere — worth ten minutes before you pay to ship it.
- □Move the suspect module to a different slot. If the fault follows the module it is the module; if it stays with the slot, the problem is the rack or backplane.
- □Identify exactly which points have failed and whether they are stuck on, stuck off, or intermittent. Stuck-on outputs usually mean a shorted driver; stuck-off can be the driver or its supply.
- □Check the field wiring on the failed points for shorts and for inductive loads without suppression diodes or snubbers — otherwise the repaired module fails the same way.
- □Confirm the rack power supply is healthy under full load. A sagging supply produces faults that look like several modules failing at once.
Not your exact model?
Search the catalog or send us the number on your unit's label — we service far more than the catalog shows.
How the 1756-L71 differs from the rest of the ControlLogix range
These share an electronics platform and fail in the same ways, but they are not interchangeable — check the number on your unit's label against this list before you ship, and before you buy a replacement.
| Part number | Distinguishing spec | Repair | |
|---|---|---|---|
| 1756-L71 (this page) | ControlLogix | Test & verify service | |
| 1756-PA72 | ControlLogix | $349 | View → |
| 1756-PB72 | ControlLogix | $349 | View → |
| 1756-PA75 | ControlLogix | $349 | View → |
| 1756-L61 | ControlLogix | Test & verify service | View → |
| 1756-L55 | ControlLogix | Test & verify service — honest verdict before you buy anything | View → |
Why a 1756-L71 fails — and what we do about it
The ControlLogix shares its electronics across the family, so these are the faults we see on this part number again and again.
Failed output points
- What you see
- Specific outputs no longer switch, or are stuck permanently on.
- Why it happens
- Output drivers fail from switching inductive loads without suppression, from short circuits in field wiring, or from sustained operation near their rated limit. A stuck-on output usually means the driver has failed short.
- What we do
- Failed drivers are replaced and every point on the module is retested individually — not just the ones reported faulty.
Failed input points
- What you see
- Inputs that no longer register field devices, or that read as permanently on.
- Why it happens
- Input opto-isolators fail from overvoltage or from surges arriving on field wiring, which is exactly the job they exist to do.
- What we do
- Isolation components are replaced and every input verified against specification.
Repair or replace a 1756-L71?
I/O modules are worth repairing mainly when the platform is discontinued or when the alternative is an unplanned migration of a working control system. Many older module families are no longer manufactured, and the surplus market for them is inconsistent in both price and quality — a repaired module of known provenance, tested point by point and warranted, is usually the more predictable option. Where a module is current, inexpensive and readily stocked, we will say so.
- New replacement
- ~$1,690–1,880 sealed surplus [REPORTED]
Market figures are collected from public listings and are indicative only — a used unit also arrives with an unknown service history and no warranty from us.
Full technical detail for this repair
The PLC Module service page covers the complete bench sequence — how the unit is tested, what gets replaced and how it is proven before it ships back — along with the rest of the family we service.
PLC Module Repair — full details →Frequently asked questions
Can the 1756-L71 be repaired?
Yes — sd/firmware faults, backplane wear are the failures we commonly repair on the ControlLogix platform. It starts with a free bench evaluation and a firm quote you approve before any work — $0 if unrepairable.
How long does a 1756-L71 repair take?
Standard bench time is 3–5 business days once the unit arrives. Rush service (+$149) moves it to 1–2 business days, and emergency same/next-day attempts are available — contact us first.
How do I send it in?
Start the repair online to get an RMA number instantly, pack the unit well with the RMA on the box, and ship it to our Dallas–Fort Worth lab with any carrier. Full packing guidance is on the mail-in instructions page.
Machine down? Let's get it back up.
Start a repair online in two minutes, or send us the part number for a free technician review.
The Fixed-or-Free Guarantee: if we can't repair it, you don't pay for the repair.
Call (817) 799-7332 · 📱 Text us a photo of your unit · Email repairs@controlboardlab.com