Dark Screen on Cowon X5

[hellomoto]

Hello,

I just received a bunch of Cowon X5 (I have 4 of them now nice collection, two are working perfectly, one is even in mint condition, with the protective sticker on the screen!), and two of them have problem. The person that sold them couldn't explain me where did these problems come from.

One can be easily repaired, the other one is definitely dead.
Anyway, the screen is dark (the battery is also dead, and the jack is desoldered, but I know how to fix that), ie i can see the screen, the letters and so on, but the screen is so dark that's it's a pain to read. How can I fix that?

Thanks you very much! (and sorry for my approximative english!)