Melsec Comms fault

Hi everyone,

An interesting question.
I have a company that has an extruder on a pie line, installed 1996 purchased from Holland. It has a Melsec FX 64MR running with now a comms fault appearing every now and then. It drops out of run mode and then goes into comms fault for about 1 to 3 seconds then goes back to run mode. Advice from a company in New Zealand told me its the battery running low. Maybe this is the case as the company has told me they have no recollections of changing it ever.

So change the battery you may say! problem is the company has no backup disk no program anywhere and the line runs everyday.

No problem I say as I purchased the developer software and said we will upload the program before we change the battery.

I have found that it requires a keyword to get into it. With no PLC notes or manual with the drawings I find myself at a dead end. The company is trying to contact the Holland company in order to get the keyword, if this dosen't work the company who sold me the software tells me to send it to them and they will hack the keyword for us.

Is this the right thing to do or is there another way? If the PLC crashes we will have to write another program from scratch! any idears on which direction I should take?

Regards,

Steve Pali

You have puzzled me a little.

What exactly is telling you it is a comms fault?

Is it a plug in unit or comms card to the FX.

And next, I wouldnt suspect the battery unless the low battery light was on.

At first my thoughts would be suspect a poor connection somewhere
maybe even inside the plc

More information please.

Hi,

There are four leds down the front of the unit. The power, batt, run and the led that shares the Prog-E and CPU-E. Power and Run are on during normal opperation, but every now and then the run led goes out drops all the outputs and the bottom led comes on CPU-E. then within 2-3 seconds the run led comes back on and the program resumes as normal. By the way this has been happening for many months now.

The unit has communication module power supply inputs and outputs on the same module. The unit has three FX 2DA modules on it.

Regards,

Steve Pali

Steve Pali said:

Power and Run are on during normal opperation, but every now and then the run led goes out drops all the outputs and the bottom led comes on CPU-E. then within 2-3 seconds the run led comes back on and the program resumes as normal. By the way this has been happening for many months now.

Click to expand...

This sounds more like a power problem. How often does it do it? Do you have something you can monitor the incoming power?

I don't think this is a battery problem. It sounds like power supply or hardware failure. But you should try to get the password and upload the program. That way you have a backup. But the first thing I would check is cables. Can you access PLC Diagnostics in GX Developer without a keyword? I can't remember. If so, you can at least get more info from the PLC about what the error actually is.

Thanks for your input guys,

I will focus my attention to the main unit and power supply. I did measure voltage coming in and during one of the faults I noticed the power light didn't go out. I also measured the output voltage which was a healthy 24vdc +.

Yes I did access the diagnostics through the developer software and got two errors the first simply said: PLC/PP comm err the second gave a 6708 operation err step 955.

One of these may be a satuation error, Getting out of my league now.

Also to answer it does it about 5 to 10 times an 8 hour shift.

Regards,
Steve Pali

Well this is what 6708 is detailed as in the help files:

Error code list[Error code 6708]
Applicable Machine FX series PLC
=====================================================================================
Error code(D8067) 6708
Error messages OPERATION ERROR
Step Number of error D8069
LED status(RUN) OFF
LED status(PROG.E) OFF
PLC ACT STATUS RUN
Diagnosis timing While in the RUN state.
Error contents and causes
FROM/TO instruction error.
Managing method
This error occurs during the execution of an operation.
When an OPERATION ERROR occurs, STOP the PLC enter programming code and correct
the fault.
Note:
Operation error can occur even when the syntax or circuit design is correct,
e.g. T0Z is a valid statement within an FX PLC. But if Z had a value of 10000,
the data register T10000 would be attempted to be accessed. This will cause an
OPERATION ERROR as there is no T10000 device available.

Ok, I guess you do need to get that keyword from the manufacturer

When you get that error, you can click the 'error jump' button to go to that step of the program. But again, that probably won't work without the keyword.

Hi
Most (older) Mitsi's have a hardwired link to the 'RUN' terminal. Have you checked this wiring has notworked loose?

IMHO there is only a 50% chance that error numbers given by a Mitsubishi product are exact or even close to what is happenning.

Some Mitsu product will give funny errors when you divide by zero.

I have also seen this type of error when the onboard DC+24 would be shorted out. Is it used to drive anything other than the input devices? If so, something should be investigated.

My 2 cents.

The comms error is just the analog cards, it could be that if it states the from/to instruction is the cause of the error then the analog card could be the cause, I have never known the low battery to be the cause of cpu error before.
You could change the battery while powered down as it will give you 5 mins min before loosing program, however if you have had this machine powered down for sometime the chances it may have an eprom fitted, in this case you would not loose the program.
but it's a brave man who would chance it giving you have no way of re-loading it.

Thanks very much everyone for your help and support you all have given me some good leads which I can try while we wait for the keyword. I will keep you informed with the outcome.


Regards,

Steve Pali

plc/pp error

Hi friend i am using mitsubishi fx1s plc. this shows a plc/pp error. Kindly help me to resolve my problem. Thanks

Just had a thought recently had a problem on a new install where occasionally the plc would go into stop & then cpu err, I noticed that if the plug (from the HMI comms) was wiggled this created the fault, however after taking the thing apart I found a bad joint between the two boards. It's possible that this being an old plc that you have either a BAD JOINT OR POOR CONNECTOR in any case if you can get the keyword I suggest you upgrade to FX3 should be pretty simple or at the very least FX2N