MicroLogix 1400 (1766) faults: FAULT LED, LCD fault code, BAT. LO battery, memory module and back to RUN

A faulted MicroLogix 1400 (Bulletin 1766) shows it first on the FAULT indicator on top of the controller: flashing red is an application fault, steady red is a controller hardware fault (1766-UM001P-EN-P, p. 149). The code itself is on the Fault Code screen of the built-in LCD, which you have to open (pp. 107–108). The user manual does not explain each major error code: it sends you to the reference manual 1766-RM001 and to the RSLogix 500/RSLogix Micro online help (pp. 108, 151, 155). This article covers what the user manual itself states. For the older MicroLogix 1500, see MicroLogix 1500 fault codes.

Controller status indicators

In normal operation POWER and RUN are on (p. 151).

Indicators on the LCD

Six indicators sit at the top left of the LCD; a solid rectangle means on (p. 150).

On the I/O Status screen, inputs show terminal status and outputs show logic status (pp. 150–151).

What the indicator pattern tells you

Reading the fault code on the LCD

1. On the Main Menu, select "Advanced Set" with the Up and Down keys and press OK.
2. Select "Fault Code" and press OK.
3. The screen shows "Major Error Code=" and the code; 0000h means no fault. Press ESC to go back (pp. 107–108).

On the same "Advanced Set" menu, "System Info" shows the catalog number, the operating system firmware revision and the boot firmware revision (p. 107).

Codes and messages the user manual names

For the full major error code list with causes and recovery, use 1766-RM001.

If a ControlFLASH update stops with "Target Module Not in Proper State for Programming", put the controller in PROGRAM mode and restart the update; with "Failed to Receive Initial TFTP Request from Target", connect the controller directly to the computer with a crossover cable or disable firewall, VPN or virus protection on the computer, cycle power and restart (p. 167).

Battery (1747-BA) and BAT. LO

• BAT. LO solid means either the battery wire connector is disconnected or the battery will fail within 2 weeks (p. 25). The controller is designed to run for up to 2 weeks from the moment the indicator first turns on; replace the battery at once (p. 145).
• Replace the battery with the controller powered on. Replacing it with power off loses all user application memory (p. 25).
• The controller ships with the battery connector connected; secure the wires so they do not block the 1762 expansion bus connector (pp. 25, 145).
• The real-time clock uses the same battery. Bit RTC:0/BL = 1 means battery low. If power is removed while the battery is low, RTC data is lost (pp. 119–120).

Memory module (1766-MM1)

• Optional 384 KB module: backup of the program and data, and a way to carry programs between controllers; it does not add memory (pp. 14, 119).
• Program Compare: with S:2/9 set, the controller will not enter run or test mode if the program in the module differs from the one in the controller (p. 120).
• It can be inserted or removed under power except during a data transaction; one inserted while the controller is executing is recognized only after a power cycle or in a non-executing mode. Write protection cannot be removed once set (p. 121).
• Load or save through "Advanced Set" > "Comms EEPROM" ("Store to MM" / "Load from MM") on the LCD (pp. 108–110), or in RSLogix 500 under "Comms" > "EEPROM" (p. 121).

Checks, step by step

1. Record before any reset: the controller and LCD indicators, the Fault Code value, and the System Info data.
2. Hardware branch (Figure 73, p. 152): check that the controller has power and the wire connections are tight.
3. FAULT flashing: Rockwell's recovery model is to identify the code and look it up, clear the fault, correct the condition causing it, return to RUN or a REM test mode, then test and verify (p. 152).
4. Will not go to RUN with a memory module fitted: check Program Compare, S:2/9 (p. 120).
5. Inputs do not match the field: compare the I/O Status screen with the field device (p. 151).
6. No serial link: "Advanced Set" > "DCOMM Cfg" puts Channel 0 in default communications (DF1 full-duplex, 19.2 Kbps, no parity, node 1) (pp. 57–59).
7. No Ethernet: "Advanced Set" > "ENET Cfg" shows the MAC address and, once assigned, the IP address; changing it needs the master password, or the LCD password from firmware 21.000 (pp. 98–101). Watch COMM 1 and look for IP CONFLICT; the Ethernet channel is disabled when status bit S:36/0 is set (pp. 276–277).
8. Expansion I/O: up to seven 1762 modules; remove power before inserting or removing one, because an arc can send a false signal and fault the controller (p. 31). On a fault, 1762 analog outputs go to zero (p. 152).

Clearing faults safely

Return to RUN only once the condition causing the fault is corrected (p. 152). Before returning to RUN, make sure the machine is safe to move, because outputs will again follow the program logic. The LCD "Mode Switch" menu sets PROGRAM, REMOTE or RUN (p. 93); holding OK for 5 seconds at power-up forces RUN and holding ESC forces PROG, and output status may change (p. 94). Holding OK for more than 5 seconds on the Main Menu toggles DCOMM instead (p. 58).

Auto Reset (pp. 127–128): from firmware 21.007, with S:36/1 set to 1 (default 0) and downloaded, a 2H, 4H, 8H or 9H fault makes the controller restart and reload the latest program and user data from NVRAM. From Remote Run it recovers to Program mode; from Hard Run, to a recoverable fault state. You still have to put it in Run; run-time data is lost and the initial data restored. It does not work if the backup is corrupted (1H) or a memory module is fitted with Load Always or Load on Error. Before you select Run, check that the restored initial data suits the machine's current state, and follow the plant's permit and lockout rules.

OS reload: an operating system upgrade clears the user program, so have a backup; Ethernet settings are kept, and SNMP must be enabled before the update (p. 159).

When it is hardware

• POWER and FAULT stay steady after checking connections and cycling power, with no "Fpga Corrupt" BOOT screen: contact Rockwell (p. 151).
• A 1762 analog module whose status LED stays off after a power cycle: replace the module (p. 153).
• Channel 0 connected to a MicroLogix 1000, 1200 or 1500, or a 1747-DPS1, with a 1761-CBL-AM00 cable: the manual warns this damages Channel 0 or the controller (pp. 16, 60).

What to record before calling for support

Rockwell asks for the controller type, series letter, revision letter and firmware (FRN) number, the indicator status and the controller error codes (p. 155). Also note whether a memory module is fitted and when the fault appears. For an engineer on site: breakdown support.