Why is the “ON” LED of the power supply unit off on a 1038/20?

Fault:

The led “ON” of power supply unit is off.

Solution:

Check the mains, if it is ok then disconnect the terminal “+V” and measure the voltage between terminals “+V” and “0V”.

If the reading is between +21Vdc and +24Vdc, section the system in order to find the short-circuit on the powering line (+V; 0V)

If the reading is lower than +21Vdc, replace the power supply unit.