PURPOSE: To detect the disorders of a large number of heating units for a short time, by a method wherein to detect the disorders of heating units, power is applied for the power application time when the color developing paper is not developed and when a heating unit is normal, the detection of the next heating unit is immediately carried out.
CONSTITUTION: Drivers 32 are connected to the circuit of data latch and picture signal drive circuit 30 and the circuit 33 for detection of heating unit break down is parallely connected to respective transistors Tr1WTr3 29 by letting diode 44 to lie. The maximum value of ON time of L1WL6 is determined to be T (the time when thermal color development paper is not developed even if power is applied to heating units 26) and L1WL6 are successively turned on. If IHOPN becomes L within a time T, the time on detection of its L level is so set as to become the next detection timing.
NISHIDA MANABU
FUTAMURA HITOSHI
