Why doesn't work the backlight of my iPod?

Hi everyone!

This is a big problem for me because I love this iPod. The ,,back” button (left button) under the clickwheel was broken. I have a donor motherboard so I just replaced the broken button. I tested the iPod after the button replacement work and everything was fine then I put the motherboard in my ultrasonic cleaner because I used flux. After the ultrasonic cleaning the backlight didn’t work. I tried with an another display but the situation is same.

I need a schematic to the repair or any advice that where can I find the backlight circuit.

Please don’t write that: ,,Just buy an another motherboard”. This isn’t worth It and I just want to repair this iPod.

Thanks in advance to the replies.