Ricoh SP 330DN Field Service Manual page 246

7.Detailed Descriptions
Unit Temperature" in the "Maintenance Mode (SP menu)".
Overheat Protection
The surface temperature of the hot roller is monitored with the fusing thermistor and the non-contact
thermistor (which is kept at a gap of 1mm from the surface of the hot roller).
If the fusing thermistor temperature becomes greater than 235 °C or the non-contact thermistor
temperature becomes greater than 220°C, the CPU cuts off the power to the fusing lamp. At this time,
SC543 or SC553 will be generated.
If the thermistor overheat protection fails, there is a thermostat in series with the common ground line of
the fusing lamp. If the temperature of the thermostat becomes greater than 185 °C, the thermostat
opens, removing power from the fusing lamp. At this time, the machine stops.
[A]: Thermostat: Operation stops when the temperature surrounding the hot roller is more than 185°C.
[B]: Fusing thermistor: SC543 will be generated when the surface temperature of the hot roller is more
than 235°C.
[C]: Non-contact thermistor: SC553 will be generated when the surface temperature of the hot roller is
more than 220°C.
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