Abstract: An image forming apparatus has developing rollers mounted to be spaced-apart from a photo-sensitive body and supplying a developing agent to the photo-sensitive body, a bias-applying part applying a predetermined bias to the developing rollers through respective current-conducting paths to the photo-sensitive body from the developing rollers, a current detection part detecting a current flowing through the developing rollers in accordance with a bias applied from the bias-applying part, and an engine control part applying a first test AC voltage having a set first frequency to the developing rollers, controlling the bias-applying part to apply a second test AC voltage having a set second frequency to the developing rollers, calculating a resistance of the developing rollers and a gap between the developing rollers and the photo-sensitive body using a current value detected from the current detection part respectively corresponding to the first and second frequencies, and setting a bias voltage of a driving co

Abstract: A self-diagnosis method for a facsimile device and a facsimile device to perform the same. The facsimile device has a modem and a line interface unit (LIU) that connects the modem to an external line. The method includes determining whether a communication path is in a normal state or in an abnormal state according to the detection of a dial tone transmitted from an outside, and/or determining whether the modem is in a normal state or in an abnormal state according to whether a diagnosing tone signal generated in the facsimile device is normally received. Accordingly, the self-diagnosis method self-diagnoses errors in the peripheral environment of the facsimile device without communicating with another facsimile device. These errors may be errors on external lines, or errors in the facsimile device, e.g., errors in a modem.