CPU Fault on Modicon TSX 3722


Thread Starter

Kukuh Prasetyo

My PLC, Modicon TSX 3722 have a serious problem. After the PLC restart, three of four the LEDs indicator (TER,IO,BAT) light on (not blinked). I have read it on manual that indicating CPU fault. I think it caused when my friend plug the PCMCIA Comm Card when the PLC running. The effect is: I cannot connect my PL7 Junior Program (PC) to my PLC. And the question is how to solve this problem? Is there any other restart mechanism (maybe like take out the CMOS BIOS battery on PC) to recover PLC to original / manufacturer setting?

I really need your troubleshooting, coz I'll use the PLC for my last task on my course.

Thank you, before and after.

Philip Scharff

If you use a PCMCIA memory card in the TSX3721/2 PLC, make sure that it is seated properly and that you use the plastic holder. If you are not using a memory card, there must be a cover in place. If this cover gets dislodged or out of allignment, the PLC can (has for me in the past) exhibit the problem you are describing.

Gijsbert-Jan Welp


There is a way to reset the TSX37 completely. It means everything is erased.

So when you do this and assuming the PLC does not have a seriours hardware fault you need to reload the application using the PL7 software.

To do this make sure PLC is powered down, press the DIAG button on the PLC and keep it pressed, Power up the PLC still keeping the DIAG button pressed. Maintain for aprox 10 seconds. Then release the DIAG button. Now only the ERR led should be flashing. (BAT led could be on because there is no battery or an empty battery)

If on the other hand after this reset your previous led state is still present you could have a serious hardware fault which means you need to replace the controller.
For this you need to contact your local Schneider organization.

Hope this helps?


Gijsbert-Jan Welp,
Technical Support Automation,
Schneider Electric Netherlands.