Problem in an Input card 1746-IA16

[AB2005]

I have an SLC 5/03 with I/Os in one of our machine. I am facing a problem with an Allen Bradley PLC Input card 1746-IA16 (85-132VAC) that voltage at its terminal block of an input (not specific, some time 5, some time 8 or some time 12 etc.) is high but related LED doesn’t ON and no operation performs by PLC for related input. I have replaced 3 cards till now due to this problem but could not understand that why it happens. The supply voltage remains between 110-120VAC.
I need assistance to overcome on this problem.

 

[Tharon]

Could the voltage be spiking occasionally causing damage to the card?

 

[Gil47]

The two bottom terminals of a 1746 IA16 is a common terminal that has to have a wire connected to it .

Is that wire connected to a neutral terminal .

Test your high input terminals to the common to confirm its good.

 

[cornbread]

What is feeding the inputs, i've had trouble when I had a solid state device feeding these types of inputs.

 

[AB2005]

I found some problem in grounding of control power transformer 380/110V which was an Auto Transformer. I installed an Isolated transformer and connected one output point (110V) with ground.

 

[adel1961]

why you did not try to get a direct line from the transformer (120v a.c.) to that input to confirm is it a plc problem or power problem !, this should be step one in troubleshooting before replacing 3 input modules!