Ppm Control; Protection Against Abnormally High Temperature - Konica Minolta magicolor 4690MF Service Manual

Theory of operation Ver. 1.0 May 2008
D. Print control temperature adjustments
• The temperature during print control is adjusted using the menu available from the con-
trol panel. The temperature can, however, be decreased only.
• Adjustment steps are 0°C, -5°C, and -10°C.
21.3.6

PPM control

• The PPM control is performed to prevent the fusing pressure roller and the fusing belt
temperatures from going down during a multi-print cycle as well as to prevent the tem-
peratures of the roller and belt edges from going up.
• If a multi-print cycle is run using media of a small size, a difference is produced in tem-
perature between the center portion of the roller/belt (the surface over which the media
moves past) and the edges of the roller/belt (where no part of the media moves past).
To inhibit this situation, the distance between sheets of media is widened and the tem-
perature of the fusing roller is thereby made uniform.
21.3.7

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 circuit on the DC power supply is turned OFF to shut down the power sup-
ply 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.
C. 3rd stage: Thermostat protection
• If neither the soft protection nor hard protection can detect an abnormally high tempera-
ture due to a defective thermistor, the thermostat operate at the specified temperature.
This shuts down the power supply to the fusing heater lamp, thus forcibly turning them
OFF.
21. Fusing section
85