It is not staying on. When it is powered on, it switches off after a few minutes.

Once power is connected, please allow 3 minutes for the device to completely boot up. During the boot up process, LEDs on the MG400 front panel will flash and then grey out. This is normal.

If the device switches off after a few minutes of operation. Please check following:

For both MG400 and MG200 if using the AC adapter, check AC power adapter if plugged in securely.

For DC power, check the fuse in DC power cable and the DC source outputs the correct voltage and current.

The MG400 unlike the MG200 has an Ignition Sense pin which allows it to switch-on and off with other electrical accessories in a vehicle.

When the Ignition Sense detects zero or low voltage, the MG400 will automatically switch off (per shutdown Timer setting in Power Control menu).

To disable / change the setting, in device Web GUI navigate to Service -> Power Control.  See image below: