1, internal motherboard has no output.

2. The connecting wire between the internal and external machines is disconnected.

3 There is no feedback from the external motherboard. Open the external terminal box and check whether there is a pulse of 0-20V between the black line and the zero line. If there is, it is the fault of the external board.

If the connecting wires of the internal and external machines are not connected properly, or there is a pulse of 0-20V between the black line and the zero line of the internal machine, if not, the internal machine board is faulty. If there is a pulse of 0-20V, it is a fault of the connecting line between the internal and external machines (pay attention to the extension of the tube).