Protection Against Abnormally High Temperature; Ppm Control - Konica Minolta magicolor 1690MF Service Manual

17. Fusing section
17.3.4

Protection against abnormally high temperature

• The machine provides protection at three different stages to prevent abnormally high
temperature of the Fusing unit.
A. Soft protection
• If the Thermistor (TH1) detects a temperature exceeding a predetermined value, the mal-
function code representing abnormally high temperature is displayed. At this time, the
power supply line is shut down.
• If the temperature of the fusing roller does not reach a predetermined value within a
predetermined period of time after the start of the warm-up cycle, the power supply line
is shut down.
B. Hard protection
• If the CPU overruns and the output level of the CPU of the Mechanical control board
becomes a HIGH or LOW level, and not a pulse output, and a predetermined tempera-
ture or higher is detected, a circuit within the Mechanical control board turns OFF the
relay to shut down each power supply line.
C. Thermostat protection
• If detection of abnormally high temperatures by soft protect or hard protect cannot be
made due to a faulty Thermistor (TH), the thermostat operates at a predetermined tem-
perature to shut down the power supply line.
• If detection of abnormally high temperatures by soft protect or hard protect cannot be
made due to a faulty Thermistor (TH), the thermostat operates at a predetermined tem-
perature to shut down the power supply line.
17.3.5

PPM control

• PPM control is provided to prevent the temperature on edges of the heating roller from
increasing during a multi-print cycle using plain media of a small size.
• The distance between sheets of media is widened according to the number of printed
pages set to be produced and the media length. This evens out the temperature of the
heating roller and thus stabilizes fusing performance of the printed toner image.
• The PPM control is provided at 20 ppm for a multi-print cycle of producing 20 pages. The
number of printed pages per minute is established as detailed below for each media size
for the 21st and subsequent pages.
• No PPM control is provided for a multi-print cycle of color printing, as it is 1/4 of the
monochrome printing.
Media conditions
A5, invoice
Media having a narrower width and longer length than above
68
Theory of Operation Ver. 1.0 Nov. 2008
PPM
14ppm
8ppm