5.1.0 successfully updated, but..font problem

[maxkhoon]

Hi all,

After follow the simple de-bricking steps, 5.1.0 can be updated even before that I have already jailbrake it with a mp3 file and such,

However, the mobi chinese book appeared as “口口口”, not all, but 30% of chinese characters look like this
I never try to de-jailbreak it before this update (5.1.0) because I see some users here said that no de-jailbreak action is needed for updating to 5.1.0,

is there any way to solve this? I have been bothered for quite a long time, really just want it to be back in original condition only,

some "way" I am thinking of:
Format it (kindle disk) through USB mode then factory reset, then download the "kindle disk" files from other users?

please guide me, thank you very much!

[maxkhoon]

please close.
thanks.