We can adjust to make copy darker from feeder using the instructions, but can not make copy darker from glass

does this happen when printing? or copying? if printing check the fuser, image /drum unit What color is the line replace that image unit, if copying does it happen thru the doc feeder ? if so place on the big glass and make a copy if it goes away the its the doc feeder slit glass that is small glass use by the doc feeder, big glass not used by the doc feeder when copying or scanning

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/normanj_7893313f0751935f

Clean the document feeder scanner glass. This is the much smaller strip of glass that is to the right of the large main glass. This strip of glass is used ONLY when using the feeder. So if you are getting a dark line when using the automatic feeder but not when laying a document on the glass then just clean the strip glass. 100% sure this is your problem. You may need to clean it several times as I have seen stuff get stuck to this glass.
Good Luck and Thank You for using Fixya.

Clean the ADF scanner glass. This is the small strip of glass that is just to the left of the large glass. Normally there is a label on the machine right by this glass that instructs you to clean this strip of glass whenever streaks appear when using the ADF or Automatic Document Feeder. Sometimes toner/dirt gets stuck on this strip of glass so clean it well using a soft cloth with some glass cleaner.
Good Luck and Thank You for using Fixya

U need to confirm that u copy through feeder or big glass...

If feeder, u need to check the feeder alignment

Need to adjust the doctor gap of developer unit if some text is darker, some text is lighter... ( can proof by printing negative post )

Is it the same result when you place the original on the glass as when you use the Automatic feeder? If copy is straight when you use the glass, then the rollers on the feeder need cleaning (with a damp cloth) -Lift the cover where paper feeds and clean grey rollers,also, and more importantly, clean the darker roller which has a plastic white roller pressed to it with a heavy spring assembly.
If copies are slanted either way you make a copy, make sure to check the paper guides in the tray are snug

1-it could come from the ADF - if makingfrom the doc feeder adjust screws in rear or ADF
2-the scanner adjust the scanner - turn off machine remove glass and adjust
3-if making from feeder the glass itself may be too dry, spray WD40 and wipe leaving a smooth surface.

is it happening whether you put it on the glass or not, or only in the feeder?

The lines are caused by some debris that is on the platen (the glass where you normally place the copies). The usual culprit is white-out smudges from a copy that wasn't completely dried yet. When you make copies using the feeder, the roller passes the paper being copied over a little section of the platen (if you pull up the feeder "lid", it'll be on the right-hand side of the big glass... it might even be marked with 2 green arrow stickers, but if not, it's the part of the glass directly under the roller of the feeder). You can just take an alcohol wipe or soak a cotton ball with alcohol or windex and wipe down that strip of glass under the roller.

Try this: make a copy from the table and then one from the document feeder. compare the two. If the copy from the table looks good and the document feeder one is bad then clean the glass on the document feeder. If both are bad remove the top glass and clean the mirrors using rubbing alcohol and a lint free cloth. you can also clean the wheels on the feeder and in the tray with rubbing alcohol if you ever have feeding problems
Hope this helps

If the problem only occurs when using the document feeder, the problem is not usually caused by the drum. When using the document feeder, try to notice where the scanner (the light assembly under your scan glass)stops just before the paper is being fed. Some multifunction machines have a small piece of glass that is separate from the large scan glass and the scanner assembly stays parked underneith it as the original is being fed over it. Most likely there is something on the glass where the scanner parks as originals are being fed thru the feeder. When putting your original on the large scan glass to copy, the mark on the glass will only show as a spot, but will show as a vertical line thru the whole copy when using the feeder.