Abstract: An image forming apparatus which detects deterioration of developer contained in a developing unit, and if it is the case, the toner is discharged out of the developing unit through a surface of an image carrying member. The apparatus is provided with a sensor to measure toner concentration in developer contained in the developing unit, a drive controller to control a supply amount of toner into the developing unit based on the toner concentration, a calculating unit to obtain average toner supply during a predetermined period, a detecting unit to detect the deterioration of the developer by comparing the average toner supply with a reference data stored in a memory.

Abstract: A method of forming an insulating layer having a planar surf on a lower wiring layer having given patterns steps at the shoulders of the patterns. On a lower wiring layer, a lower insulating layer is formed and a heat resistive material is coated over the lower insulative layer to form a substantially a planar top surface and to fill cavities appearing in the surface of the lower insulating layer with the material. Then, etching is carried out to preserve the profile of the surface of the coating layer and to remove the coating layer at portions where through-holes are to be formed. Any cavities in the surface of the lower insulating layer remain filled with the material after etching. An upper insulating layer is deposited on the exposed lower insulating layer and the remaining part of the coating layer.