Protection Against Abnormally High Temperature - Konica Minolta magicolor 5550 Service Manual

Theory of operation Ver. 1.0 Nov. 2006
20.3.13

Protection against abnormally high temperature

• The main body provides protection at three different stages to prevent abnormally high
temperature of the fusing unit.
1. Soft protection
2. Hard protection
3. Thermostat protection
A. 1st stage: soft protection
• If the thermistor/1 or the thermistor/2 detect a temperature exceeding a predetermined
value, the malfunction code representing abnormally high temperature is displayed. At
this time, the heater lamps are turned OFF forcibly and the initiation of any new print
cycle is prohibited (abnormally high temperature detection control).
B. 2nd stage: hard protection
• The following hard protection control is provided if the CPU overruns and becomes
unable to detect an abnormally high temperature.
1. The thermistor/1 or thermistor/2 detect a temperature exceeding a predetermined
value.
2. The remote signal for the corresponding heater lamp of the DC power supply is
forcibly turned OFF through the MFP board.
3. The triac on the DC power supply is turned OFF to shut down the power supply to
the corresponding heater lamp.
4. The heater lamp is forcibly turned OFF.
5. The temperature detected by the thermistor/1 or thermistor/2 is decreased to a
level below the predetermined value.
6. The remote signal forcible OFF of the corresponding heater lamp is reset so that
power supply to the heater lamp is resumed. This operation is repeated until the
CPU recovers to be able to detect the abnormally high temperature condition. This
control allows the power supply to the corresponding heater lamp to be shut down
before the thermostat operates, inhibiting the fusing unit from being damaged.
20. Fusing section
101