ML1400 Starting problem

I am using a ML1400 for a project, the problem arising is that the PLC is not powering up completely.

The POWER LED and the Fault LED, both are blinking. The display is blank. The PLC is going ON...OFF...ON...OFF...ON.....

I searched the internet for the problem, but could not find any relevant piece of information.

Any pointers to what may be the problem.

PS: The power is given via a 24V SMPS, with proper grounding.

If this belongs somewhere else, please move to the respective thread.


Thank You

What is the complete catalog number of your ML1400?

Do you have another PS to try?

It sounds like the power supply is undersized, either for the MicroLogix alone or for one of the circuits connected to it.

Isolate the power supply and the MicroLogix only, and see if the controller still goes through that cycle.

What it supposedly means from the User Manual:

The POWER LED never flashes as a diagnostic indicator.

If it's turning on and off, the controller supply power is also turning on and off, or the controller is rebooting.

If the controller is receiving continuous steady power and is still cycling on and off, it is defective and should be replaced.

First things to try.

1) Put a meter on the 24vdc to see if it is also going on and off.
2) Unhook all other loads except for the PLC power supply and try again.
3) Try a larger supply

Based on the symptoms I would suspect the PS or some other device on the 24VDC than I would the ML.

First of all, thank you for your valuable inputs. Answering to them below:

Mickey said:

What is the complete catalog number of your ML1400?

Do you have another PS to try?

Click to expand...

I am using 1766-ML1400. Yes, I do have another PS to try with, and I did that as well. No difference.

Ken Roach said:

It sounds like the power supply is undersized, either for the MicroLogix alone or for one of the circuits connected to it.

Isolate the power supply and the MicroLogix only, and see if the controller still goes through that cycle.

Click to expand...

No, the power supply is a proper 24V DC supply. The same PLC was working on the 24V DC supply earlier, suddenly it starts behaving like this. The power supply is only for the PLC. There are no other connections in the circuit. I was programming the PLC and hence had taken it out of the panel.

Lancie1 said:

What it supposedly means from the User Manual:

Click to expand...

I did refer the UM. Did not find any pointers to the problem I have been facing and hence posted here. That was kind of you to post the reference to the User Manual.

Ken Roach said:

The POWER LED never flashes as a diagnostic indicator.

If it's turning on and off, the controller supply power is also turning on and off, or the controller is rebooting.

If the controller is receiving continuous steady power and is still cycling on and off, it is defective and should be replaced.

Click to expand...

No, the power supply is giving a constant 24V DC. I used a multi-meter and tested it and also connected another PLC in the circuit. The other PLC is working fine, but not this one.
I also figured a problem with the controller and would be contacting Rockwell for this now.

DamianInRochester said:

First things to try.

1) Put a meter on the 24vdc to see if it is also going on and off.
2) Unhook all other loads except for the PLC power supply and try again.
3) Try a larger supply

Based on the symptoms I would suspect the PS or some other device on the 24VDC than I would the ML.

Click to expand...

1. Used a multi-meter, the supply is constant 24V DC.
2. The PLC in this case was the sole load for the PS.
3. Do you recommend trying a supply more than the recommended 24V DC for the PLC. For more clarification on the problem, please read the replies I have given above.

Thank You.

I am using 1766-ML1400.

Click to expand...

Complete cat. no. please.

Mickey said:

Complete cat. no. please.

Click to expand...

Oops! My bad. Should have done this before.

I am using 1766-L32BXB. SER B. FW 11.

MWA said:

Oops! My bad. Should have done this before.

I am using 1766-L32BXB. SER B. FW 11.

Click to expand...

Thanks, what I was looking for was to make sure your unit was in fact a 24VDC input powered unit. It is of-course.

I have seen power supplies that even though the specification would indicate it is powerful enough to supply your PLC but
could not handle the inrush to start the PLC. If you have a bigger power supply you might try it.

In case it wasn't clear from previous posts, unhook all add-on I/O modules and all input and output connections on the base unit and retry.

If the problem is resolved begin by re-connecting the inputs and outputs one at a time. If the unit is still functioning then begin reconnecting the add-on modules one at a time.

Of course if the problem wasn't resolved by removing all connections then the base unit needs to be replaced.

MWA said:

...The POWER LED and the Fault LED, both are blinking. The display is blank. The PLC is going ON...OFF...ON...OFF...ON.....

Click to expand...

On the MicroLogix 1400, flashing of the POWER and FAULT LEDs, along with no LCD display, indicates an incorrectly supplied voltage. This might often be seen when a user accidentally applies AC voltage to a DC controller, as Mickey was verifying was not the case here. The controller is not cycling ON and OFF, it's indicating that it's not happy with the supply it's receiving.

MWA said:

...I was programming the PLC and hence had taken it out of the panel.

Click to expand...

Why you had to take it out I'm not sure, but is there any chance that you mixed up controllers before re-fitting one to the panel?

I just want to be clear that the catalog number you quoted was indeed off the one and the same blinking controller that you've put back in on the 24VDC supply in the panel, and not off the side of the other working controller that you had wired in with the blinking one. We have several different models of ML1400 on the shelf. It's easy make a mistake. Can you please re-confirm that the blinking controller is indeed a 1766-L32BXB, and out of curiosity, what is the catalog no. of the working controller that you tried?

I have acidentally wired AC to DC controllers in the past, with the same symptoms you are presenting with.

George

Mickey said:

Thanks, what I was looking for was to make sure your unit was in fact a 24VDC input powered unit. It is of-course.

I have seen power supplies that even though the specification would indicate it is powerful enough to supply your PLC but
could not handle the inrush to start the PLC. If you have a bigger power supply you might try it.

Click to expand...

As of now, I don't have a bigger supply unit, but if I have access to one in future, I would try one.

bernie_carlton said:

In case it wasn't clear from previous posts, unhook all add-on I/O modules and all input and output connections on the base unit and retry.

If the problem is resolved begin by re-connecting the inputs and outputs one at a time. If the unit is still functioning then begin reconnecting the add-on modules one at a time.

Of course if the problem wasn't resolved by removing all connections then the base unit needs to be replaced.

Click to expand...

Sir, the particular application does not need any extra I/O modules apart from the base PLC and all are disconnected. It is a lone power supply connected to a Base ML1400 PLC without any I/O modules.

Also, there are no I/O's wired up in the base module at the moment. For further clarification, read my reply to Geospark.

Geospark said:

On the MicroLogix 1400, flashing of the POWER and FAULT LEDs, along with no LCD display, indicates an incorrectly supplied voltage. This might often be seen when a user accidentally applies AC voltage to a DC controller, as Mickey was verifying was not the case here. The controller is not cycling ON and OFF, it's indicating that it's not happy with the supply it's receiving.

Click to expand...

The supply is 24V DC and the controller was working perfectly fine with the same supply a day ago. It is no AC voltage, only 24V DC as checked via a multi-meter as well.

Why you had to take it out I'm not sure, but is there any chance that you mixed up controllers before re-fitting one to the panel?

Click to expand...

Sir, the specified controller was not mounted in a panel. It was sent to me for testing and update in the program from the site. It was working when I received it, but the problem started after that.

I just want to be clear that the catalog number you quoted was indeed off the one and the same blinking controller that you've put back in on the 24VDC supply in the panel, and not off the side of the other working controller that you had wired in with the blinking one. We have several different models of ML1400 on the shelf. It's easy make a mistake. Can you please re-confirm that the blinking controller is indeed a 1766-L32BXB, and out of curiosity, what is the catalog no. of the working controller that you tried?

Click to expand...

I have not yet put it back onto the Panel. It is still on my desk and I am using the same 24V DC that was being used earlier when the controller was working very fine. All the controllers that I have are the same Catlog 1766-L32BXB that operate with 24V DC. Another controller of the same Catlog number is working perfectly with the same SMPS, that rules out the problem of the SMPS completely.

I have acidentally wired AC to DC controllers in the past, with the same symptoms you are presenting with.

Click to expand...

Thanks for this info. Now I know what to check first if this kind of an error occurs.


Thank You.

MWA,

Thankyou for further clarifying the situation. Up to now your comments read as though the supply in question was in the panel, not on a desk.

MWA said:

...The supply is 24V DC and the controller was working perfectly fine with the same supply a day ago. It is no AC voltage, only 24V DC as checked via a multi-meter as well.

Click to expand...

Having thought the 24VDC SMPS was in the panel, I was more implying that you might have accidentally connected an AC supply whilst the controller was out of the panel. We now know better what you were doing and that only one power supply is in question here.

Personally, I'm not a big fan of using Switch-Mode Power Supplies for bench testing PLCs. They switch at very high frequencies. Less expensive SMPS can be noisy because of poor suppression and frequently power cycling them while connected to a controller on a desk "might" do harm over time. If used in a panel, power cycling tends to be less frequent. Again, it depends on the quality of the SMPS.

MWA said:

...the particular application does not need any extra I/O modules apart from the base PLC and all are disconnected. It is a lone power supply connected to a Base ML1400 PLC without any I/O modules.

...there are no I/O's wired up in the base module at the moment...

...It is still on my desk and I am using the same 24V DC that was being used earlier when the controller was working very fine. All the controllers that I have are the same Catlog 1766-L32BXB that operate with 24V DC. Another controller of the same Catlog number is working perfectly with the same SMPS, that rules out the problem of the SMPS completely.

Click to expand...

I think you have answered your own questions here. If the SMPS was the only PS you have had connected to this controller, and another BXB controller is working fine, then it looks like the controllers PS may have gone faulty.

My initial suspicion would be the SMPS did the damage through frequent power cycling, but it could just be a controller with a suspect PS that would have gone anyway.

I found RA's reference to the aforemention flashing LEDs...

It's TechConnect level: 567396

George