Patent ID: 6965741

Claim:
A thermal fixing device, comprising: a fixing member that thermally fixes the medium to an other medium, the fixing member being elongated in an elongated direction and having a main portion and an end portion aligned side by side in the elongated direction; a main heater that heats the main portion of the fixing member; an end heater that heats the end portion of the fixing member; a main portion temperature detector that detects a first temperature at the main portion of the fixing member, an end portion temperature detector that detects a second temperature at the end portion of the fixing member, a diagnosing unit that judges whether the main heater and the end heater are operating properly based on the first temperature and the second temperature; a power supply starting unit that starts supply of power to the main heater and to the end heater; a main warm up timer that measures a main warm up time from when the power supply starting unit starts supplying power to when the first temperature reaches a predetermined main warm up temperature, the diagnosing unit further judging whether the main warm up time measured by the main warm up timer exceeds a predetermined acceptable time limit and determining that the main heater is not operating properly when judged that the main warm up time measured by the warm up timer exceeds the acceptable main time limit; and an end warm up timer that measures an end warm up time from when the power supply starting unit starts supplying power to when the second temperature reaches a predetermined end warm up temperature, the diagnosing unit further judging whether the end warm up time measured by the end warm up timer exceeds a predetermined acceptable time limit and determining that the end heater is not operating properly when judged that the end warm up time measured by the warm up timer exceeds the acceptable end time limit, wherein the acceptable main time limit is the same as the acceptable end time limit.