Ricoh Aficio BP20N, Service Manual

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SYSTEM LAYOUT
G144/G145 6-10 SM
Safety Features
The machine has the following countermeasures to prevent overheating:
1. 1st protection device: Hardware shuts down when the machine temperature
reaches 207 C.
2. 2nd protection device: Software shuts down when the machine temperature
reaches 220 C for 3 seconds
3. 3rd protection device: The thermostat measures the temperature of the hot
roller and cuts off main power to the fusing lamp when the temperature reaches
a pre-determined level.
Safety Devices
1. Fusing power is cut when the front cover is opened.
2. LSU power is cut when the front cover is opened.
The temperature of the fusing unit’s cover surface remains at less than 80ºC. This
protects the user. A caution label is attached where the customer can see it easily
when the rear cover is opened.
6.3.5 LASER SCANNNING UNIT (LSU)
The LSU converts video data into an electrostatic latent image on the surface of
the OPC drum. This is accomplished by controlling the laser beam and exposing
the surface of the OPC drum with the laser light. A rotating polygon mirror reflects
the laser light onto the OPC drum. Each side of the polygon mirror equals one scan
line.
The OPC drum turns as the paper feeds, to scan the image down the page. A
/HSYNC signal is created when the laser beam from LSU reaches the end of the
polygon mirror. The signal then goes to the controller. The controller detects the
/HSYNC signal and adjusts the vertical line of the image on paper. In other words,
after the /HSYNC signal is detected, the image goes to the LSU to adjust the left
margin on the paper.