hi, i'm new here

i have a question about an allen bradley slc 5/04. As we all know when you initially power up the processor it goes through a self test where all the lights flash and it does all it's other little checks.
I have 1 5/04 in our shop which will occasionally skip all that power up stuff. the red fault light will just come on by itself, solid, not blinking. when this happens it dumps the program and will not allow any communication. after cycling power a few times we eventually get communication back and are able to reload the program.
anyone ever see this before? any ideas what i should look for? tia

Hi Shadrach and welcome to the forum

Unfortunately I have seen this before and it is usually a sign of a failing processor.

I did have an instance recently that was caused by a bad chassis. Do you have another chassis and power supply you could stick it in?

TWControls said:

Hi Shadrach and welcome to the forum

Unfortunately I have seen this before and it is usually a sign of a failing processor.

I did have an instance recently that was caused by a bad chassis. Do you have another chassis and power supply you could stick it in?

Click to expand...

I had some time last night so i tried a brand new power supply, same thing happened. i took the old processor out and put a brand new one in, same thing happened. i ended up putting the old power supply back in and the processor came back up like it should. at this point i had to leave to pick up my young'ens so i just left it alone. i do plan on ordering a new rack today.

Hi,
I have faced this problem once with the SLC. But in my case the CPU was not at all communicating. so we replaced the CPU and it worked. Like, as you said after some tries the communication comes back, so does it has got anything to do with the Input/Output cards may be analog cards in the local chasis. Just try removing all the I/O's and put a another sample program without the I/O's to see if the problem comes again...
--Arun

Welcome to the forum Shadrach! For future reference, do tell if the rack was to blame...

Shadrach said:

I had some time last night so i tried a brand new power supply, same thing happened. i took the old processor out and put a brand new one in, same thing happened. i ended up putting the old power supply back in and the processor came back up like it should. at this point i had to leave to pick up my young'ens so i just left it alone. i do plan on ordering a new rack today.

Click to expand...

DOH!...it helps if you move the jumper from 240 vac to 110 vac.

The new power supply seems to have done the trick. Had the machine powered down all weekend. Came in Monday morning and it powered up just fine.

DOH!...it helps if you move the jumper from 240 vac to 110 vac.


You can be lucky that was all that happened. In the RSA we use 220v and one was shipped to us jumpered for 110v. You can guess what happened next. Fried processor and power supply