I am currently experiencing some printing quality issues in the LaserJet Printer.

[KM44]

The printer actually prints all the characters but as soon as I take the printed paper out of it, some characters start to fade out and disappear.  I don't know if the problem is with the toner or imaging drum.  Both are genuine HP products.  When I verified the imaging drum, I found some excess toner on it.  Should I clean it? 

[Echo_Lake]

@KM44
Thank you for posting on the HP Support Community.

Let's check the toner cartridge and imaging drum for damage.
Remove the toner cartridge and imaging drum, and then inspect both for damage.

1. Lift the scanner assembly, and then open the top cover.

2. Examine the memory chips for damage.

3. Slide back the cover to expose the imaging drum surface.

4. Examine the surface of the imaging drum.

5. Close the top cover, and then lower the scanner assembly. 
   Click here to complete the troubleshooting steps.

Hope this helps! Keep me posted for further assistance.
Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution.

[KM44]

Hello, thank you for helping. I have already checked the imaging drum and it has traces of excess toner on it.  Can this be the reason of why the characters disappear on the paper after being printed?

[Echo_Lake]

@KM44
Thank you for posting back.

To get the answer to this question, Yes! that is one of the reasons the printouts are being printed that way. 
Are you able to print without any issue? Would you require any further assistance?
Please mark my public post as an accepted solution if you feel I have answered your query.

[Repairatrooper]

Can you clarify, this is a laser printer, which uses powdered toner, you say it is fading, do you mean that the image gets wiped off the page? If so then likely either your fuser has a problem, or your media is too heavy for the current heat settings.

[KM44]

Therefore can I clean the excess toner on the imaging drum with a tissue paper or should I change it? Though it is still at around 80% full. Find in the photo the missing and faded characters when I printed a test page.

[KM44]

@repairatrooper 

Yes, it is indeed a laser printer.  After printing immediately, I can see the characters but immediately after 2 3 seconds some of them start to disappear.