Quick Tips to Solve Your PLC Problems Without Losing the Program

Mitsubishi PLC repairs

Is your PLC finally dead now that you’ve reprogrammed the channels on the I/O cards about 10 times? (Did you think we didn’t know you did this? Everyone does this.)

Did your Mitsubishi PLC suddenly just “lose” its program?

Or maybe your GE Fanuc PLC faulted and now the little red light is on and you can’t get your error codes to clear?

Then you would definitely NOT be alone.  We hear these tales of woe day in and day out from manufacturing plants and shops of all sizes.

In a perfect world you would perform monthly or bi-monthly maintenance checks on your PLCs, but even if you manage to do this, many of the most common PLC problems are not caused by lack of maintenance.

Machine age and environmental conditions are often at the heart of the problem.  Assuming you have ruled out ridiculously obvious problems such having the wrong cables or loose cable connections, a few of the evil PLC poltergeists include:

  • Power fluctuations or surges
  • Over heating
  • Blown power supplies
  • Blown I/O cards
  • Bad I/O channels
  • Bad cables/loose cable connection
mitsubishi plc batter

However, another frequent PLC problem is absolutely a maintenance issue – bad batteries.   Yes, this really happens as it did recently to this Mitsubishi FX-64MR-UA1/UL (see top photo) which is an obsolete PLC.  Obsolete PLCs can be repaired, but this may add some challenges to the repair process. 

If you’ve been neglecting to replace your PLCs back-up battery (a very inexpensive item!), bad things are sure to happen.  If the red fault light indicates “battery status” you are in imminent danger of losing your program.

If you do not have a current program on hand to reload after you’ve replaced the dead battery, then you are in even more trouble.  (WARNING:  If the red battery light comes on don’t down the power! First, get the program backed up BEFORE you attempt to change the battery(s).) Whether you are the boss or the operator, this is not a situation you want to find yourself in.  Let the finger pointing begin!

In almost all of the above mentioned cases, you will need to remove the PLC unit and have it repaired.  If the PLC is still under warranty, you will need to contact the OEM.  If not, you will need the services of a reliable  industrial electronic repair shop that does PLC repairs.  The best repair shops will provide free evaluations, accurate quotes and a warranty on both parts and labor.