Who knows how to repair a copier machine? (ricoh 4422)?

I can help but you need more details in your question? I looked up your machine online, it's over 5 years old. If it's never had any work done on it it probably needs a cleaning blade, when you said you adjusted the exposure and it doesn't help is a giveaway. When you say dark is it lots of dark lines ? The exposure can be adjusted internally but it's vary rare and usually is just concealing another problem. If you really want to try something get into to scanner area, (unplug it ) using a flashlight/torch take a look at the mirrors they should be bright and shiny if not let me know and we will go from there.