I had spare time (read: was bored) and I decided to make a USB Jig for my Galaxy to reset its custom binary count.
What is this?
When you root a Galaxy S2, the bootloader keeps a record of how many custom firmwares you flash. I’ve flashed a couple of ROMs already so my phone’s “custom binary count” was 4. Basically, once you’ve rooted your phone or flashed a custom ROM, you’ve voided the warranty.
Samsung knows if you’ve voided the warranty by checking your “custom binary count”. If it isn’t 0, then they presume you’ve voided the warranty and can refuse to service your device. It doesn’t matter if you go back to stock firmware because your “custom binary count” won’t go down. Simply put, once you flash a custom ROM, your warranty is bye bye.
If you run a custom ROM, you also get this huge yellow triangle with an exclamation mark on it to signify you’re not running an official firmware.
Back to the point, this USB Jig will reset the “custom binary count” to zero and get rid of that yellow triangle. The Jig is basically an imitation of Samsung’s tool to kick the device into recovery mode. In short, the Jig will make your phone look like it’s never been rooted before.
The Jig can also save you if you screw up flashing your bootloader and your Android won’t boot into Download mode.
How to make one?
There are numerous guides on the internet but in short, you need to make 301Kohms of resistance between pin 4 and 5 of the USB plug that goes into the phone. You’ll actually have to unsheath the plug since normally pin 4 isn’t connected to anything.
Personally, I just got a plastic one and cracked it open (since it can be put back easily with a bit of super glue while rubber ones can’t be replaced - apart from that, no difference).
How to use?
I had problems with it not working at the start.
What I had to do was first take out the battery from the phone once you’ve powered it off. Plug in the jig, then place the battery back in. It should automatically boot into a special Download mode that says “Erasing download information succeeded”.
You can now unplug the jig and reboot your phone. Voila! “Custom binary count” is zero. No more yellow exclamation mark. Yet the phone is still rooted. Win!
I kept the cable intact in this picture because I wanted to be able to reuse the cable but it’s totally optional.