· On 09th of Aug’ 2017 at around 10:30 PM both ML 200 processors went into Fault Mode with Error code “E030”. On resetting the PLC was not getting into RUN mode.
· Meanwhile it was identified that the processor was in fault mode since 6 nos. I/O cards were not getting recognised by their respective bases. Rack #2 Slot #8&10 digital output cards ( 2 nos. 2MLQ-RY1A), Rack# 6 Slot #8&11 digital output cards ( 2 nos. 2MLQ-RY1A) & Rack#8 Slot#2 digital output card ( 1 no. 2MLQ-RY1A) were not getting recognized by the CPU.
· All the above mentioned cards were finally changed & the system was made ready.
· The error code “E030” indicates that there is module mismatch. In this case since the I/O modules were not recognized by the CPU therefore it was creating a mismatch with the hardware configuration defined in the system.
· After opening the cards it was found that one of the 100 KΩ ,250mW resistor (R1: SMD resistor) in the feedback circuit was in open condition. Circuit details shown below.
· The resistors were replaced and the cards were tested in the test jig . The cards were recognised by CPU. Further the D/O’s were forced from the logic as well as made high through program to check their functionality & they were found working satisfactorily. There was no time delay observed for the D/O operation & the D/O’s were turning ON/OFF instantaneously w.r.t the Force command given from PLC logic.
· The PCB circuit for the D/O card was further traced back to the extent possible to understand the role of R1 resistor. Details given below. (this diagram may not be accurate. if anybody have the correct ML200 DO card diagram plz share)
· The D/O module receives signal from the CPU vide Connector#2 shown in above drawing. The LG make FDIO I/C switches on the corresponding Transistor (TR#1,2,3 &4) based on the input received from CPU. Once the transistor is ON the subsequent relay (NY5W-K) is turned ON & this in turn makes its potential free N/O contact.
· As per the circuit diagram the R1 resistor is connecting the +5 V DC with the LG FDIO I/C. It is assumed that any open circuit condition due to failure of R1 resistor will result into malfunctioning of LG make I/C thereby creating problem in recognition of corresponding D/O module.
· PLC faukt log says 11 times system reset made by key switch at a span of an hour.
· The resistor was of 250 mW. With 5 V Dc the current will not be sufficient to burn in i2rt effect except may be possible if it occurred multiple times with switching surge.
Now here I am stuck. How i can conclude/ correlate that the failure of R1 resistors in all the five cards are due to no of startrs/resets.