When a PLC Goes Bad…


Earlier this week, a customer of ours who runs a sorting and distribution facility ran into a problem. A big problem. It was an issue severe enough to shut down their entire sorting line. One of their PLCs (as well as its accompanying IO systems) had completely failed and refused to power back on. The fix would require ordering spare parts, which meant a long delay due to supply-chain issues caused by the COVID-19 pandemic.

Because this was an emergency for the customer, costing them money to keep their machinery stalled, we had to find a solution quickly. So we bypassed the PLC completely and modified the VFD’s configuration to run non-stop using their manual mode setting.

This should, of course, only be done in emergency situations like this, where there is no other alternative but to run the machine. But it did get the customer up and running while we wait on the parts to fix the system.

Below, we detail how we swapped the VFDs to manual mode in order to let them run without stopping.

“So we bypassed the PLC completely and modified the VFD’s configuration to run non-stop using their manual mode setting.”

Click the button below to download the PDF version of our PowerFlex 525 manual mode guide.

PowerFlex 525 Manual Mode Switch Procedure


1. Change the Start Source of the VFD



2. Save the
to Keypad

3. Change the
Frequency Command
of the VFD


4. Save the
Parameters to

5. Exit to Home Screen

a longer step-by-step if you prefer:


01. Make sure that you are on the home screen and there are no errors.

02. How to set the start source to keypad:
– Press select (center key)
– Locate the PO parameters and select enter (cycle parameter types using the up and down arrow)
– Locate parameter PO46 (Start Source)

03. Use the up and down arrows to cycle to the number 1 (Keypad)
– Selection 5(ethernet) is the default it should be placed back on this setting using the same steps to properly communicate with the PLC.
Note: moving to a parameter and waiting for approximately 2 seconds will populate the parameter description.

04. Press Enter

05. Press the escape key 3 times to go back to the home screen and save the new parameters.