If your Quadra no longer boots or some application you installed has messed things up, no problem! It is fairly easy to make a recovery SD card and then restore your Quadra firmware. Note that this will completely erase your Quadra: Any settings or data you had on it will be erased by this process.
Items you will need:
1. A computer (Windows/Mac/Linux) with an SD or micro-SD slot or USB adapter.
2. A 16GB or larger micro SD card. Ideally a micro SD card with adapter so it can be used in standard or micro slots. Note that if you get a 32GB micro SD card or larger, you can also use it to make backup, so a good investment.
Note: If you don't have or can't afford these items, you can contact firstname.lastname@example.org and request a factory restore SD card. This is a free service, but we request that you return the SD card when done so we can keep this service free.
1. Download and install Balena Etcher
2. Download the Quadra firmware
3. Insert the SD card into your computer's SD slot
4. Launch Balena Etcher
5. Select "Flash from file". Select the Quadra firmware you downloaded above
6. Select the drive containing the SD card (its size should match your SD card size) under "Select drive"
7. Click "Flash"
This will take several minutes and will create your Quadra installer & recovery SD.
Unplug or don't connect a monitor at this point as the installation is automatic if one is not connected. Plug the SD card into the TV box and plug in the power adapter.
The front panel LED (light) will turn red while booting and flashing the internal ROM. This will take about 7 minutes. When it is done, the LED will turn blue.
Finally, unplug the TV box, remove the SD card, connect the monitor, keyboard and mouse to the TV box and reconnect it to power. After a few seconds you will see an "Armbian" logo and after a few seconds more, the LED will turn blue indicating Linux has started. A few moments later, you will see a login screen. The default password will have been reset to "1n0v@t0" (the "0"s are zeros). Then you will see the full desktop appear. You'll want to change your password again.
If you won't need the SD card for other things, keeping it as your recovery SD is helpful as you won't have to create it again, making recovery fast and easy.
It is also a good idea to make periodic backups! This will give you a way to still use your Quadra if the internal storage becomes corrupted, with all your data intact to your last backup.