Issues with 1769-IF4 module

[rejoe.koshy]

hey guys,
I am stuck with a peculiar issue with a micrologix plc unit with an analog input module as an external I/O.

I have a micrologix 1500 series PLC with a 1769-IF4 analog input module which was working fine but recently the analog module started malfunctioning & I replaced it with a new one.After this when I power up , the plc goes in to fault mode (starts blinking red) , but as soon as I switch the key from run to program back to run modes the fault disappears & it starts working.This happens every time I power up.

Added to this when I am running my application , which involves a timer, the PLC goes in to fault mode when the timer stops timing(preset value is reached).

The fault that is displayed in the software is F81- "expansion I/O hardware error"

I am totally confused since the module replaced was identical to the old one.
& the field transducers are working fine.

ps: on careful observation I found a blown transistor in the PCB of the old analog module

I have uploaded the pdf version of the program for your reference

Pls help!!

 

[Mickey]

Check and double check the connection(s) between the expansion module(s) and base unit, end cap. Unseat and reseat might help also.

Make sure you have proper grounding.

 

[rejoe.koshy]

The connections have been checked & reseated.Is there any special grounding system that needs to be followed?

 

[Mickey]

Nothing special, just follow the book. See paf

 

[rejoe.koshy]

I suspect there could be voltage drop in external 24 v supply.Should change over to internal bus supply & try?

I have been struggling with this problem for a week now!..pls help!