Sharp AR-651 Service Handbook page 256

<<Procedure of the "surface potential sensor control check">>
Set the value for the number of detected abnormalities of the drum surface potential control
(08-420) to "0".
Set the value for the drum surface potential setting (08-421) to "0" (valid).
Set the value for the auto-start print volume setting 1 of the image quality control (08-803) to "0"
(valid).
Perform a test printing.
Check the control status of the surface potential sensor (05-242) and number of detected
abnormalities of the surface potential sensor (08-420).
If the value for 05-242 is except "4" and the value for 08-420 is "0", the status is normal.
Return the value for the auto-start print volume setting 1 of the image quality control (08-803) to "2".
The check is completed.
AR-651/810 TROUBLE SHOOTING 5 - 106