Overheat Protection - Ricoh R-C4 Service Manual

IMAGE FUSING AND PAPER EXIT 21 July 2006

6.13.7 OVERHEAT PROTECTION

If the hot roller temperature becomes higher than 231°C, the CPU cuts off the
power to the fusing lamp. At the same time, SC543 is generated.
Even if the thermistor overheat protection fails, there are four thermostats in series
with the common ground line of the fusing lamp. If the temperature of the
thermostat reaches 210°C, one of the thermostats opens, removing power from the
fusing lamp. At the same time, SC542 is generated and the machine stops
operating.
In addition to these protection devices, there is a backup temperature control circuit
on the SBCU. If the thermistor protection fails, or if a short circuit occurs on the
PSU board.
If the temperature exceeds 250 °C:
• This backup temperature control circuit switches off the fusing lamps
• The machine issues SC544.
6-84