Start with the status LEDs
RUN, STOP, ERROR and BATTERY LEDs narrow the problem in seconds. Note their state before touching anything.
Check the power supply
Measure 24 V DC at the CPU and I/O modules under load. Sagging supplies cause random faults that look like software problems.
Back up the program first
Before any repair or reset, upload and save the program and data blocks. A flat battery or memory fault can erase the logic.
Isolate I/O faults
Force or monitor the input from the programming software. If the LED changes but the logic does not, suspect the module; if neither changes, check the field device and wiring.
Communication errors
Inspect connectors, terminating resistors and cable shielding. Check addresses and baud rates match after any module swap.
When to call us
CPU faults, repeated memory loss and failed modules need bench repair. We support Siemens, Allen-Bradley, Mitsubishi, Schneider, Omron and Delta.
