Unity Booting Issue | How to fix the bootloader with STLINKv2
When do I need this?
First make sure it’s the bootloader which is broken, not the firmware. This is not for a broken firmware, always try to flash the firmware again using the Focbox app first! The main symptom of a broken bootloader is that it does not turn on at all. Often a light goes on, and turns off after a few seconds. The Unity comes with the bootloader pre-flashed, so if the Unity just comes out of the box this is also not required (unless it’s broken out of the box ofc).
What do I need?
- An STLINKv2 serial debugger. Get the original (or a really good fake), as fakes are sometimes wired wrong.
- A bunch of female to male jumpers. I used these 25, as I had some laying around. They were slightly too large (they do fit, but it’s for one-time use), so get one size smaller if you ordering for this.
- A Windows computer.
- The ST-LINKv2 41 utility.
- The Bootloader binary 57. This is the bootloader and firmware bundled together.
How do I do this?
- Disconnect the unity from the battery and any other connectors.
- Remove the orange cover.
- This reveals the unity with a separate PCB on top. The separate PCB is the Bluetooth module.
- Remove the Bluetooth module. Take note of the connector the module is plugged into. This is the connector we will be using to flash the bootloader.
- Take the jumpers, and connect them as follows to the ST-LINK (phase wires are oriented at the top). Take a look at your ST-LINK for the corresponding connections.
NOTE: You don’t need to plug your unity into your battery. It is powered by the ST-LINK.
- Connect the ST-LINK to your computer.
- Open the ST-LINK utility.
- Click connect on the top row (Looks like a mains plug with a lightning bolt). This should connect to the unity. It should look somewhat similar to this:
- Click on
Open fileand select the bootloader binary.
- Click on
Program & Verifyon the top row. This should show something like this:
- Check the start address. (Unlike the photo) it should show
- Click start!
- After this is done, disconnect the ST-LINK inside of the Utility. This is the Mains plug with the red cross on it.
- Disconnect the ST-LINK from the computer.
- Unplug the Jumpers from the Unity.
- Put the Bluetooth module back in its position.
- Put the orange cover back.
- Connect the phase wires, remote and battery back into the Unity as normal.
- Try it out!
Now you should be able to use the Unity like normal.
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