Laser printer print defects - Fading print with bubbles

Problem	Possible Cause	Solution
fading print with bubbles	Toner cartridge drum not grounded properly	With no ground path, the drum cannot discharge. The negative charge on the drum repels toner and leaves a white page with bubble print. 1. Replace toner cartridge. 2. Check the drum ground spring and reconnect it, if necessary. 2. Replace the engine controller board