Copies are printing out light on the top half of page

See troubleshooting section of user manual at page 65
Troubleshooting - Sharp AR-5516 Operation Manual [Page 66] ' ManualsLib

There are a few potential reasons why your copier might be printing faint copies:

1. Low toner levels: If the toner in your copier is running low, the copies it produces may appear faint or light. To fix this issue, you will need to replace the toner cartridge.
2. Dirty or clogged nozzles: If the nozzles on your copier's print head are dirty or clogged, they may not be able to produce a full, even layer of toner on the page. To fix this issue, you can try cleaning the nozzles or running a nozzle check to see if any are clogged.
3. Wear and tear on the print head: If the print head on your copier is worn or damaged, it may not be able to produce copies with the same intensity as a new or well-maintained print head. In this case, you may need to replace the print head to fix the issue.
4. Incorrect print settings: If the print settings on your copier are set to a low quality or low density setting, the copies it produces may appear faint. To fix this issue, you will need to adjust the print settings to a higher quality or density setting.

If none of these steps resolve the issue, it is possible that there is a malfunction or defect with the copier that will need to be addressed by a professional. In this case, you may want to consider contacting the manufacturer or a customer service representative for further assistance.

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Check toner setting (saving)
Replace / refill toner
If the problem still exists, then clean corona wire
Gestetner F104 Operating Instructions Manual

Have you calibrated your printer after changing ink cartridges?

There are many different companies that sell compatible toner, and the quality varies greatly. You should try getting your money back from the company you bought that toner from, and find a new supplier if you can't get it from Gestetner. Premier is a company that sells compatible toner for many different machines, and they usually get pretty good reviews.

The partial faint copy in your case is most likely toner on the laser optics. It is NOT the fuser.
Since you are indicating a toner dusting or spillage issue into the bottom or perhaps paper tray area then this toner is also most likely on the laser optics. This blocks a portion of the laser light and results in a faded or sometimes even blank portion of the copies. Dis-assembly of a portion of the machine is going to be required to clean the laser.
It is located between the toner cartridge and the Drum/PCU unit at the bottom of the machine. So if you open the front door where the toner cartridge comes out. The laser strip glass would be below and to the right of there the toner is. Some of these still have a small metal cover/clip that you can remove and then slide the laser strip glass out and clean it then re-install.
Hope this helps. If this makes no sense or does not help then it might be a good idea to call a service company and have the machine cleaned.
Good Luck and Thank You for using Fixya.

There may be spilled toner inside the copier, Free the drum and paper way of toner an ensure the toner container is not over full. do proper cleaning and the copier will be okay.

Bad fuser.

If the copy count is around 150,000 or higher and you haven't replaced the developer as well, it should be replaced. That symptom can cause light copies if it hasn't been replaced every 150,000 cycles.