Since the two of you have not solved the problem, it is okay to put here together to solve.
Because I have been contacted by quite a lot users who have upgraded the RC firmware by mistaken,
From the success stories of the fix. All the conditions that can increase the success rate are listed below.
why stucked in OSINIT?
Because FW5RC experimentally improved the read efficiency, however, we did not take into account that most users use SD cards that are not as fast as our sandisk red 32GB, so in the time limit set by the firmware, slower SD cards cannot load the full kernel in time, so they will get stuck in OSINT.
You must have an enough fast SD card, a genuine sandisk red 32GB is the best all we know. it can increase the success rate to load the recovery kernel.
DO NOT USE SDXC card. or older years small card.
best way is preparing two SD card. one sandisk red 32GB, one is other SD card which you can use on the EZ-Jr before(FW4). swap cards is faster on retry.
1. format both SD card with FAT32, 32KB file allocation unit size.
2. put recovery kernel on sandisk 32 GB SD
3. put 1.04 kernel on other SD
4. plug sandisk into EZ-Jr, power up, wait at OSINIT 10 seconds or more. shutdown
5. plug 1.04 kernel SD into EZ-Jr, power up.
if you can enter the kernel, it means firmware downgrade successful. if not, repeat step 4 and 5.
Other conditions: If it is a battery model, please ensure that the battery power is sufficient, if it is rechargeable model, please plug in the charging cable.