PLC 5 multiple outputs stuck high on multiple cards

Hey there, I have a PLC 5 in which I have outputs 1,5,6,and 11 stuck high. The LEDs on the card do not indicate the output is one, but there is 120v at the terminal strip. I have replaced the card and noticed that the replacement also was high on these same outputs.

I dont think its regular leakage current because all the outputs on this card go to motor mags or solenoids for valves, and they have enough to power to pull in a valve because 1 and 11 are a two way valve that was fried due to this issue.

If I lift the wires from the terminal stip they are still hot, so it is not feedback from the circuit.

I have pulled the card out and tested continuity across the stuck outputs and the common on the card. They are fine, no continuity.

I may have done some other stuff that i cant think of at the moment. im kinda dumbfounded at the moment...

Any thoughts?

What is the model number of the I/O module in question?

Was this a working system and suddenly stopped?
Can you move the card to a different slot?

Card model number would help. You may be thinking you are SOURCING voltage FROM a card common, when in fact you are SINKING voltage TO a card common, or you may have a relay card which doesn't care.

Switching between processor types can screw with your head, thinking about AB vs. DirectPLC. First time I almost had to learn how to troubleshoot all over again...

jschapansky said:

Hey there, I have a PLC 5 in which I have outputs 1,5,6,and 11 stuck high.

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It's been a while since I worked on a PLC5, but I'll try to help anyway.

jschapansky said:

The LEDs on the card do not indicate the output is one, but there is 120v at the terminal strip.

Click to expand...

Ok, so the logic is not turning on the output but there is still voltage present.

jschapansky said:

I have replaced the card and noticed that the replacement also was high on these same outputs.

Click to expand...

Was this a new card or one of unknown history? Is there a posibility that your system has dammaged these outputs before?

jschapansky said:

I dont think its regular leakage current because all the outputs on this card go to motor mags or solenoids for valves, and they have enough to power to pull in a valve because 1 and 11 are a two way valve that was fried due to this issue.

Click to expand...

So you already know about the leakage issue from types of output modules.

This sounds like a direct acting double solenoid control valve. If I was to guess it's a D05 hydraulic valve. D05 valve coils can be tough on PLC outputs. The holding current when the spool has shifted is around 1 amp. The current draw before the spool has shifted is somewhere around 6 to 8 amps.

Is there a possibility that the spool is stuck? If so then perhaps the moment the coil burned up it killed the output point. Then perhaps the PLC tried to energise the other coil and the same thing happened there.

jschapansky said:

If I lift the wires from the terminal stip they are still hot, so it is not feedback from the circuit.

Click to expand...

Ok! But have you tested for voltage when you have a load attached to the output in question? Is it a full 120 or is it only around 70 volts?

jschapansky said:

I have pulled the card out and tested continuity across the stuck outputs and the common on the card. They are fine, no continuity.

Click to expand...

Did you use the "diode check" setting on your meter? Did you reverse the leads? I once experenced a triac output module with a bad output (like your complaint). Triacs are just scr's in opposed pairs. In my case one of the scr's was conducting for every half cycle.

PS. I'm curious do you have individual fuses on your outputs?