U7-1 how can i solve it

A worn out copy cartridge can cause this problem. It is the PR timing belt is worn out. If the edge of the timing belt is ok, the exposure lamp under the machine is not working good. This lamp is located above the copy cartridge, and it provides light to the timing sensor so it can read the hole on the timing belt. The bad timing sensor itself can cause these types of problems.
If this light is ok, a broken copy recieving unit can cause these types of problems. It cracks and hangs .

The other area that can cause problems is with the developer motor. Either the linkage is getting stuck, or the belt is so worn out it will not drive the xerographic drive process. Sometimes the motor itself will bind inside, the gears inside the motor can fail.
The main board can cause these problems, but usually it is realiable.
Good luck.

Hello sir; you have a bad copy cartridge, replace it !