Disclaimer; whatever you do to your cart is at your own risk. I bricked my Ez4 original cart by using GBA Exploader where the cart was not seen by NDS or GBA. Well if the system cannot see the cart you cannot update the firmware by holding right shoulder button. Well GBA Exploader can always see EZ IV and you can switch between writing modes by pushing the left shoulder button between psram and NOR. I would say the best thing to do would be to just not use GBA Exploader with EZ4 and I think this should have been made more clear. However I had fun playing with recovering my cart from a bricked state. So in order to restore the EZ4 you will have to have the USB EZ-Writer device designed to write to the old EZII and EZIII GBA carts that did not have the mini SD slot like the EZ4.So essentially the ez4 is just an ez3 cart with a mini SD slot added. So you can write to the cart memory regardless of the state of the firmware and loader. So you might have to play with some ezmanager software versions, but I believe 2.22b (last version I believe) works. Anyway after you get all your USB drivers going for the writer and the drivers are contained in the usb folder of the software and I only tried this on XP so I don't know how newer versions of windows would work. Anyway replace GBA loader with a full dump of the firmware (not the update). The full firmware dump is around 4 MB, so if the size is around 2MB then you probably just have the update and not the full firmware. I think the ez4 kernel collection is available on GBA temp downloads. So with the ez-manager software started and the light on the programmer on showing the drivers are seeing the device, replace GBA loader file with the full firmware dump and rename it to whatever the name of the GBA loader is called inside the SYSBIN folder. With the software started if you unplug the usb cable to the ez-writer the software should see the writer and cart and ask you if you want to update and if you say yes and it will try to update. Sometimes the update will get stuck and you can unplg the cable from the writer to get it to progress to teh end. If you have to unplug then you will not successfully update the firmware and will have to try again until you get the update to complete. It takes patience and I also wrote the 4mb firmware dump with GBA exploader to the psram and the nor of the cart before getting the firmware to complete. It seems to be a bit of voodoo to get the ez-manager to complete the update. Sorry for this poorly written guide, but I wanted to share how I successfully unbricked my ez4 and your mileage might vary and again whatever you do, you do it at your own risk. Contact me if you want me to give your cart a shot at revival and I would do it for a few bucks if you ship in continental US.