Allen-Bradley SLC 500 PLC —> CPU fault what does mean

[sam_sam_sam]

If you do not have the E-rom chip it gives you this error light ON
If you put the E-rom chip in the unit the run light come on and CPU fault light is on

This PLC is outside of the machine when testing it
Does this matter if outside of the machine to get this CPU fault light to be ON

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I found out why the CPU fault light is on

Look at the picture of the ic chip

[Topcat]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

^
I dont think that one is going to make it. Going to attempt to find a replacement?

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

^
I dont think that one is going to make it. Going to attempt to find a replacement?

You are so very right about this

So far I have not much luck yet still working on it

[R_J]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I don't think you will find a replacement ic, easier to find a used SLC500
It might be a OKI M82C55A-2 ; MSM82C55A-2 QFP44.
or AT89S52-24AU

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I don't think you will find a replacement ic, easier to find a used SLC500
It might be a OKI M82C55A-2 ; MSM82C55A-2 QFP44.
or AT89S52-24AU

I trying to find a used one that does not have a CPU fault error

I am just going to use it for parts

Thanks for the information

[Curious.George]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I found out why the CPU fault light is on

Look at the picture of the ic chip

I'd be looking to see what has caused this. The chip, on its own, would hardly experience such a fault.

Does this connect to the field or any "high-er voltage/power" devices, elsewhere?

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I'd be looking to see what has caused this. The chip, on its own, would hardly experience such a fault.

Does this connect to the field or any "high-er voltage/power" devices, elsewhere?

This machine has it own 24 volt power supply ( transformer type ) that is not regulated and has 120 volt transformer that is step down from 480 volt main power supply to the machine

I have try to figure out what part of the switch controls to this part of the circuit board and see if one the 24 volt transformer is having some type of issue before I put in another PLC unit

This area where I work the power company has issues with power brown outs on one or more phases not a total brown out but a phase in balance of any where from 3 to sometimes more than 8 % enough to see light dim

It is not unheard of us losing a phase for some time and then we have to call the power company and let them know that we lost a phase

[redwire]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

The site's dirty power could make a big surge between two phases, or to ground. You might have an issue with bad grounds between mains power, the PLC and the I/O.

The control transformer (480-120V) primary could be wired Delta or Wye, and a Delta could go overvoltage if one phase got lost. NEC requires a control transformer (480-120V) secondary to be grounded, so the PLC power should have a neutral/ground there.
The 24VAC transformer I would see if the secondary is grounded somewhere or it is floating?

I would find out why the chip blew up on the CPU module. That looks like a good surge hit it.
If an I/O card got zapped or is shorted, it could put high voltage on the backplane back to the CPU module.
It's something I would also check, so the replacement CPU card doesn't get damaged.

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

The power company sends power that sometimes is not very good

Here is why I say it not unheard of that you will hear a jack fuse blow down the street and we loose a phase of our incoming power from the power company

Down the street there are automatic feeders that switch from one feeder line to another we have had where it has gone crazy and put us in dark brown out to no power right back to power and may do this 3 or times in a row

I have had to call the power company about this before

I have even have had this happen at my house

Now do not get me wrong it does not happen very often but it has happened before

But what happens more often is that I have work at night when the power has brown out but where does not go out completely it does not do this on all phases at the same time

It has happened in daytime as well and it might do a few times in a row then settle down for awhile and do samething again some time later in day again

I have sat in the break where there drink machines are and I can tell when the power is not stable because the compressor motor start changing pitch and sometimes it does for few minutes to sometimes for hours this not all the time but it happens


Today I was in the main office and I sitting at the computer and could hear the transformer for the battery back up unit humming a lot more than normal most of the time I do not hear it

I actually got up and went to where the battery back up unit to if I could hear it changing pitching which it sometimes it has done before

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

My luck finding a good working PLC is not very very good
I have one more of them coming and then I have to go different route

Two for less than $30.00 each two at about $55.00 each
One of the $50.00 I returned to the seller for a refund
The last one that I bought was $75.00 the seller tell me that this one the CPU fault light is not ON or flashing so we will see what happens with this one

There is a company called OneStop that I used them before and they were able to help with another PLC for one of our other machines

That had a very unusual fault it would run for a while and then just shut down then when power cycle the machine it might come right back ON and sometimes it would take a while for it to come back ON

I had to change the power supply board and the PLC has been working very good for at least 3 years now

But the problem with using them is that it takes a while to get the remanufactured PLC and I will have to send them the E-Rom chip to make sure that it works correctly or not

It would take about 10 working days before I would have one that if the they get a working one or not

The cost of a remanufactued is about $400.00 plus the fee for making sure that the PLC works with the E-Rom chip plus the cost of the E-Rom chip from the machine manufacturer will cost any where from $200.00 to 400.00 so maybe for about $1000.00 compared to $6000.00 for a retro fit PLC plus installation cost could be any where $2000.00 to $4000.00

The power supply board seems to have a shorted rectifier and seems to have a shorted switching power regulator ic chip and what else I do not know yet I have not gotten that far yet

So I do not trust weather or the E-Rom chip is good or not


This machine was made in 2008

[TechGeek]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

While you're at it, PLEASE install some kind of filtering device between the AC powerline and the PLC.

[eccerr0r]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

That's weird, never thought to see of low power CPU chips blow chunks. The bond wires are much thinner than of power transistors and die bonds will fail fairly readily?

But anyway, chances of finding a replacement IC is going to be problematic because it looks like it indeed is a QFP 8051 OTP/mask programmed microcontroller and not an 8255.

Time to redesign the whole system ... ?

[redwire]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

If a power suppy and CPU are dead from some thunderbolt, it's time to add transient protection.

If the PLC is powered from one phase and any inputs are off another phase, that can cause the same damage and kill input/output cards.

You can get SPD's (surge prot devices) which are MOV's as 480V 3-phase Wye power protectors, they are not super rugged, just ordinary MOV's with fuse and LED's to go in the panel. Better than nothing.
Schneider SDSA4040
Eaton surge protection

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

If the PLC is powered from one phase and any inputs are off another phase, that can cause the same damage and kill input/output cards.

This is an interesting point and this might be the case It would not be easy to change it because not every thing is in one cabinet

If a power suppy and CPU are dead from some thunderbolt, it's time to add transient protection.

There was no thunder storm that day so I do not know what happened to the PLC

However the week before I had some problems getting the PLC to come on I do not know if this is related or not

However that chip that has the hole in it seems to control the outputs on main part of the PLC because all the output LED lights are all ON

Not only that the POWDER light the RUN light the CPU light the FORCED I/O light are all ON

When you first turn on the PLC light and CPU light are on then the other two comes a few seconds later ( this is with out the E-Rom chip in it but it does the same thing with it in there )

I am also thinking that the auxiliary output card may have a problem as well because one or two of output LEDs lights are also and it did not matter which PLC I put it in but even those PLCs had the CPU was on so it might not mean anything but we will have to wait until I have a working PLC unit to see what other damage was done

One more thing is that the switching power supply the switching power regulator ic chip was shorted on the output pins to the transformer which could have power surge the voltage on the power supply

I replaced the switching power regulator ic chip and the optic sensor and the power supply came back to life and I also recapped the board I ran the power supply for at least 2 hours with no problems

[redwire]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

By thunderbolt I meant a big mains transient, as if Zeus tossed a thunderbolt.

I think it's worth it to look at the aux output card, if it's damaged then for sure you need some transient protection. The surge could come in there or on AC power.

Note Allen Bradley 1992 changed the SLC 500 series chassis wiring, series A had smokable resistor, series B has a 1MEG so the 24VDC side is almost floating. AB recommends DC Neutral connected to earth ground.

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

By thunderbolt I meant a big mains transient, as if Zeus tossed a thunderbolt.

I think it's worth it to look at the aux output card, if it's damaged then for sure you need some transient protection. The surge could come in there or on AC power.

Note Allen Bradley 1992 changed the SLC 500 series chassis wiring, series A had smokable resistor, series B has a 1MEG so the 24VDC side is almost floating. AB recommends DC Neutral connected to earth ground.

Do you have a website link where they talk about these changes that were made and why I would be interested in reading this

Thanks for for sharing this information

[redwire]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

It was in Allen-Bradly backplane documentation but I forgot it. https://ab.rockwellautomation.com/Pr...#documentation
SLC 500 Modular Hardware Style user manual, Grounding guidelines
SLC 500 Fixed Hardware Style install and operation manual, Grounding guidelines

They have an entire doc 1770-4.1 on grounding PLC's. That has a lot of MOV's too.

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

I did get a PLC that seems to work but I do not know what is on the E-Rom but it power ON and turn on 3 relays and I put it in 2 other PLC and it does get the same exact results all three of them

So I have come to the conclusion that the E-Rom ic chip has something wrong with and another PLC E-Rom ic chip does not work correctly either

So now I have to request a new E-Rom from the machine manufacturer

The auxiliary input and output cards might not be good either but I do not have a definite answer to this question until I have a new E-Rom chip

One note

In the manual it does mention that if the CPU fault is ON that you might have a bad E-Rom chip
But the way it worded it says control chip I am wondering if it the same thing

[sam_sam_sam]

Re: Allen-Bradley SLC 500 PLC —> CPU fault what does mean

Ouch this hurts

I got in touch with the machine manufacturer and when I saw this quote I almost fell over

$1200.00 something for E-Prom ic chip

I wonder if this is because it is obsolete item and they know it and we are paying it

I have bought E-Rom ic chip before for there micro computer boards and there prices where a little high but not this bad