Protection Against Abnormal Conditions - Konica Minolta bizhub 200 Service Manual

19. Fusing section
E. In standby (for Europe area)
Standby temperature
19.3.3

Protection against abnormal conditions

• The machine provides protection against abnormally high temperature of the Fusing Unit
in the following four steps.
1. The Fusing Roller Thermistor and the Fusing Roller Sub Thermistor are connected
via a short-circuit connector. If a connection failure occurs in the Fusing Roller
Thermistor or the Fusing Roller Sub Thermistor as a result of the thermistor's not
being connected via the short-circuit connector, a heater remote is cut off. If the
above condition is detected, the machine displays the malfunction code represent-
ing a warm-up failure and prohibits the initiation of a new copy cycle. (This is an
ordinary detection of a warm-up failure.)
2. When the Fusing Roller Thermistor and the Fusing Roller Sub Thermistor detect
230 C due to an abnormally high temperature as a result of a faulty triac or remote
°
driver, the machine displays the malfunction code representing an abnormally high
temperature and prohibits the initiation of a new copy cycle. (This is an ordinary
detection of a malfunction of an abnormally high temperature.)
3. A different protection is provided when the CPU overruns, becoming unable to
detect the malfunction of an abnormally high temperature. If the Fusing Roller
Thermistor and the Fusing Roller Sub Thermistor detect 250
the Power Supply unit is turned OFF through the Mechanical Control Board and the
power supply to each of the heater lamps is shut down. If the detected temperature
thereafter decreases, the heater relay is turned ON again and supply of power to
the heater lamps is resumed. The sequence of these operations is repeated until
the CPU recovers from the overrun and becomes able to detect the malfunction of
an abnormally high temperature. This control allows the power supply to each of
the heater lamps to be shut down before the corresponding thermostat operates. It
thereby suppresses damage to the Fusing Unit itself.
4. If detection of the abnormally high temperature through approaches 1, 2, and 3
above is not possible due to a defective thermistor or other reason, the thermostat
comes into play to shut down the power supply to each of the heater lamps. The
Fusing Roller Thermostat is rated at 250
mally high temperatures)
68
Fusing Roller Thermistor
(TH1)
Mode1: 190 °C
Mode2: 190 °C -> 165 °C
Mode3: 165 °C
C. (Ordinary protection against abnor-
°
Theory of Operation Ver. 2.5 Jul. 2006
Fusing Roller Sub Thermistor
(TH2)
C, the heater relay of
°