The leds of the modules have been left flashing (digital inputs and outputs).

• The first thing we thought was that the modules were damaged, we discarded it by installing new ones and they were still flashing too,

• Then we thought it was a failure in the power supply or in the source, but it was discarded by measuring the power supply and it is stable,

• Then we also thought it was a failure in the bus connectors, but we ruled out bus damage because other connectors were installed,

• An output module was also added to the hardware (followed by the failed modules) to rule out bus damage and the LEDs on the bus do light up normally when the output is activated, while the previous ones were still flashing,

• To the output modules that are in failure the address range was changed, thinking that they were being overwritten in the program, it was changed in the program to the new addresses and in the hardware and the modules worked correctly, but the failure was passed to two modules of a remote station, then they were returned to the addresses that had in the modules with failure and the signals of the modules of the remote station remained fixed or do not activate (in outputs) and those in the CPU rack remained flashing,

• In order not to affect so much the production, the necessary signals were programmed in the module that was added and to another input module that was available.