Compact Logix 5330 Output Module Problems

Greetings Everyone:

The system in question is a Compact Logix 5330 with (1) 24 VDC sink/source input module, (1) 24 VDC source output module, and (1) AC/DC out module.

The recurring problem we are having is that, on occasion, all the LED's on the 24 VDC source output module will go out at which point we lose all our outputs from our PLC, without the processor seeing this malfunction as a fault per se, amazingly enough.

It has been noticed that this problem has not recurred all that frequently since a ventilator fan was placed blowing across the PLC. However, we did take note that when the ventilator fan was moved away for cabinet maintenance, the problem with the output module manifested itself once again. So, excessive heat seems to be a instigating factor in this case.

Additionally, the procedure that is in use to 'reset' the PLC is to turn the processor key from run, to rem, to prg, then from prg, back to rem, and then back to run. We usually have to repeat this cycle with the processor key twice, at which point, the output LED's usually come back on almost in an instant thereafter.

Any suggestions that anyone may have for helping properly resolve the issues with this PLC would be greatly appreciated.

Thank you for your time.

Best regards,
Max

Madmaxx:
It's not common to hear what you have explained, only one thing comes to my mind, are your connection between modules tight, they have a lock, if one of them is a little bit loose it will cause a problem like yours.

widelto said:

Madmaxx:
It's not common to hear what you have explained, only one thing comes to my mind, are your connection between modules tight, they have a lock, if one of them is a little bit loose it will cause a problem like yours.

Click to expand...

Agree.
Also, are you exceeding in any way the Max rating for the card?
Overload of some sort will kick in the self protection of the module and that may be what you are experiencing.
Calculate the total load of your outputs and find out if you are over the rating of the module.
As you mentioned excessive heat, it will derate the actual module ratings quite a bit in a hurry too.
Can't think of anything else at the moment.

I'm sure you can write a bit of code for diagnostics of each module.
Most of them come predefined (Built in status registers and such that you can read), just look on the AB site and take it from there.

From your description it seems that the backplane connection is OK but we can't be certain until you describe how you monitor it.

Is the output module a 1769-OB16P with electronic overload protection ?

Generally this is only a point-by-point protection against short circuits and overload, but it does reset automatically when the circuit cools. The keyswitch action might just be coincidental.

With regard to the controller not faulting; the default behavior if an I/O card loses its backplane connection is to fault the controller, but this can be disabled. Check your RSLogix 5000 program to see if the module is configured to fault the controller if the connection fails.