Prints Contain White Spots or Horizontal Lines, How to Solve?

depends on the printer (different printers employ different systems to apply ink), but a common solution is a simple cleaning of the printer mechanism. Look in the owner's manual for maintenance or troubleshooting. If you don't have the manual, you can certainly get one on line from the manufacturer (or many other places, probably). If the manual does not say, then the manufacturer website will almost certainly have something about it, somewhere.

the drum has a horizontal crack ... should be replaced

If you prints contains white spots or horizontal lines, it means your print heads may has been clogged--especially if you haven't used your printer for some time. Clean the head by running the printer's utility program. If you can't find it, try accessing it from your Print & Fax system preference. Select your printer from the list, and click on Options & Supplies. In the resulting window, click on Utility. You may need to clean the head several times for best results. Be sure to print a test sheet between cleanings to avoid damaging the nozzles.

If cleaning doesn’t work, then you can turn off the printer over night, and run the the cleaning process once again. Generally speaking, the sublimation ink will not dried any more and will be easier to clean.

If you have a chronic problem with clogged heads, make a habit of turning your printer off at night. (Turn it off at the printer, not at the power strip.) In some models, doing so will engage a capping mechanism that protects the nozzles.

Most printer utilities will let you print a test sheet that uses all the printer's ink cartridges. If you haven't printed a color image in a while, print a test sheet before printing a large file--it wastes less ink than a bad print.

Wash the print head.