Does the PLC output appear as ON during online monitoring? If online monitoring shows that your output is off, yet the output LED turns ON, it means that the output driver has probably blown.
The output drivers on T22H-npn are controlled by the ULN2003A. You can try to swap the ULN2003A that controls output 1-4 with the other chips and see if the output problem has shifted. If so, it confirms that the output driver is fried.
The most likely reason for the output driver to blow is over current. Wrong polarity connection to the PLC's power supply input can also knock out the output driver.
You can purchase the ULN2003A driver chip easily from any Radioshack or any local electronics store, or you can purchase it from us. Please send your request to sales@tri-plc.com if you wish to purchase the ULN2003A chip.
