Troubleshooting The GE Series 90-70 PLC System

Welcome to PDF Electric and Supply Company troubleshooting series: Troubleshooting the GE Series 90-70 PLC System.

PDF Supply has a large inventory of GE 90-70 parts, and we’ve created this article to assist users with troubleshooting techniques.

Step 1: Inspect Power Supply Status

The first step to understanding the GE Series 90-70 PLC status is to inspect the LED’s on the front of the power supply and CPU. When the green power LED on the power supply is on, it indicates that all power in and out of the power supply appears to be functional.

Note: The Series 90-70 has 7 different power supply modules. See all the modules here

Power Supply Pictured IC697PWR713



Step 2: Check Power Supply Fuse

If this LED is off, first check the fuse inside the power supply door. If your fuse is good, then most likely you will need to replace the power supply.



Step 3: Inspect CPU Power-Up Status

If the power supply is good, then move to the CPU located next to the power supply. A green ‘OK’ LED on the CPU means it has passed its power-up test. If this LED is not on, then replace your CPU and/or memory card mounted on the side of the CPU because there is most likely a hardware failure.

Note: The Series 90-70 has 21 CPU modules. See all the modules here



Step 4: Inspect CPU Run Status

A green ‘RUN’ LED indicates that the CPU is in run mode and is solving program logic properly. Your problem could be with field devices or the I/O Enable switch inside the CPU door. It could possibly be in the improper position. If this LED is off, we will describe a troubleshooting procedure later in this video.



Step 5 – Inspect ‘ENABLE’ LED

Finally the green ‘ENABLE’ LED should be on, which indicates that there are no faults in your CPU, and the I/O Enable switch is in the correct position inside the CPU door. Your processor is fully functional, and other non-CPU issues could be at fault.



Step 6 – Inspect ‘MEM PROTECT’ LED

A fourth LED remains off unless the key switch is in the ‘MEMORY PROTECT’ mode. This LED exists only with the latest series of the 90-70 CPU’s.



Step 7: Inspect Battery Status

If you have a dead battery, your CPU may go into ‘STOP’ mode on a power cycle because you have no program.

  • It is always good to setup a regular battery change out procedure to limit the loss of a program. You must carefully replace the battery while the PLC is powered up.
  • In many cases, there are two battery connectors; one for the new battery, and one for the current installed battery. Install the new battery before removing the old battery.
  • DO NOT power down your PLC System, or you will most likely lose your program during the battery change out process.


Step 8: CPU Out Of ‘RUN’ Mode

The most common failure of the Series 90-70 PLC is the ‘RUN’ LED is off, which generally indicates that an incident has put the CPU in ‘STOP’ mode. Connect your programming unit to the RS-485 Serial Port on the PLC CPU, and then navigate to the fault tables in your programming software.



Step 9: View Fault Tables

There are two basic fault tables; I/O and CPU. There you will find time and date stamp faults that have caused your system to leave ‘RUN’ mode. In many cases, it will identify rack and slot positions of the failed module. Once you have fixed the issues creating the fault, clear the fault tables so that any additional faults will be logged at the next power-up. Continue this process until your GE Series 90-70 PLC System is back up and running.



Step 10: Additional Support Options

We hope our troubleshooting guide has helped you track down the problem in your PLC system.

Should you to need to repair or replace any parts for your GE Fanuc 90-70 PLC, please contact us at 1-800-360-6802 or visit our website at

We offer:

  • Repair
  • Repair with Exchange Credit
  • Remanufactured – 3 year warranty
  • New