Overheat Protection - Ricoh Aficio MP2550B Service Manual

Image Fusing and Paper Exit
Starting and stopping the fusing lamp power every second causes fluorescent lighting in
the room to flicker. To reduce this flickering, use SP1-108 to change the cycle from 1
second to 2 seconds.
Fusing soft-start
In addition, whenever the fusing lamp power switches on, full power is applied to the fusing
lamp gradually, not all at once. This prevents the power in the room from dropping suddenly.
This feature is known as "Soft Start". The machine does this by gradually allowing more
power to the fusing lamp over a number of zero-cross cycles of the ac supply. The diagram
below shows full power being applied gradually over the duration of 3 zero-cross cycles.
Soft start occurs every time the fusing lamp power switches on (i.e., at some time during
every second), not just at the start of the print job.
This feature is effective to counter flickering lights. However, generated noise
increases if the setting is changed from the default. If a radio or a TV is close by
the machine, the noise may have some effect on the image or sound.

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.
D017/D018/D019/D020 6-74 SM