Dark copy what will be the cause?

That means that you have to clean copy glass , lenses, ccd,...maybe even laser unit if you know how.
On digital machines dirty optics means light copy, on analog oposite, dirty optics dark copies.

Just one more question how do you mean " charge toner"?

Dark copies in that machine means the drum it's getting old. If adjusting the exposure to light makes the copies better, then the drum is the culprit.

does the lamp under the platen glass turns on when copying? if not you might need a new exposure lamp...but if you get an image but its very dark, if you are mechanically inclined you can clean the mirrors and lens and the bottom of the platen glass because after many years of use dust will make the optics dirty and cause the copies to be very dark. hope this helps.

don't know the model of machine, but usually caused by the drum unit or toner cartridge. many machines have both drum and toner in 1 unit. try replacing.

Sounds to me like the drum needs replacing, and likely the developer too. There is probably a haze of toner still on the drum. You can check by opening the right side cover and looking at it. Is there toner on the drum (green cylinder). It may not be too obvious depending on how dark the copies are. GENTLY wipe a tissue across it after making several copies - it should be clean if the drum is functioning properly. If it is, it could be the fuser that is wearing out, but I'm leaning toward the drum. As I said, if you need to replace this, it is a good idea to do developer at the same time, because these machines tend to be a little sensitive.

are you using brother products or generic. using some generic supplies will cause this problem

have you replaced the drum??? are you using brother oem toner???? generic toner will give you all kinds of problems

the dark lines are caused by these things so check.

the thin strip of lamp dirty, or a light is bad
the drum has a dark toner ring around it, change
the fuser is dirty or is bad

Please give modell number and name. Cant give you a advice out into the blue :-)

How do the copies look? Most commonly dark print is caused by defective generic supplies or dirty laser scanner.

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