Thanks for your kind advice and I wil be guided accordingly. However, when the spring tension in the Fuser Unit is increased the machine gives error code, as if the motor overloaded in while engaging in raising the lower roller.
Be sure to setup correct the paper settings, otherwise the fuser unit could be the problem.
In my Fuji Xerox DC 9000, when copies or prints made, the images are bit crisp but smudged, not fixed properly (though heater section is working). So the toner stuck on the heat rollers is transered over subsequent printed matter. One can wipe off the toner from print/copy easily. Also in 2-sided copying the reverse copy is even much duller than the front side image of the copy/print. I will grateful for all your kind help.