Datasheet

OK now you can plug in your 5V 2A or 4A or larger wall
adapter into the HAT/bonnet. This will turn the green
LED on but nothing will display on your matrix yet
because no software is running!
Check that the Matrix plugs are installed and in the right location
© Adafruit Industries https://learn.adafruit.com/adafruit-rgb-matrix-plus-real-time-clock-hat-for-raspberry-pi Page 29 of 39