Samsung ML-2851ND/XAZ Service Manual page 28

2.2.3.1(b) Memory
Flash Memory : It stores System Program and downloads the System Program through PC Interface, and in case of
model for export it compresses the PCL font, then stores it.
- Capacity : 16M Byte (NOR Flash)
- Random Access Time : 10 us (Max)
- Serial Page Access Time : 50ns (Min)
DRAM : It is used as Swath Buffer, System Working Memory Area, etc. when printing.
It stores Font List, compressed into Flash memory, on DRAM and uses it as PCL font in case of model for export.
- Capacity : 32M Byte(Basic), up to 160Mbyte (Factory Option)
- Type : SDRAM 100MHz/133MHz , 32bit
2.2.3.1(c) Sensor Input Circuit
Paper Empty Sensing
The Paper empty sensor (Photo Interrupter) on the HVPS informs the state of paper to CPU whether it is empty or not
with operation of the actuator.
When cassette is empty, it detects the fact by reading the E20 of CPU, and then informs the fact by displaying the RED.
Paper Feeding/With Toner Cartridge Sensing
When paper passes the actuator (feed sensor part), it detects the signal of Photo interrupter, informs the paper feeding
state to CPU, and then sprays the image data after certain time.
If it doesn t detect the feed sensor within 1sec. after paper is fed, paper Jam0 is occurred (LED will be display Orange
color). The fact whether the developer is inserted or not is detected by CRUM. After the developer is mounted, the sub-
CRUM can read the information of toner cartridge from contact with CRUM involved in toner cartridge. If the information
of toner cartridge is invalid, it will show invalid sign on LED.
Paper Exit Sensing
It detects paper state whether paper gets out from the set with operation of exit sensor on the HVPS and actuator on the
frame. Paper detects the on/off time of exit sensor by reading D22 of CPU, and the normal operation or jam information
is informed to the CPU.
The paper JAM2 is informed. (LED will be display Orange color)
Cover Open Sensing
The Cover open sensor is located on the HVPS. After the front cover is opened, +24VS (DC fan, Solenoid, Main Motor,
Polygon motor part of LSU and HVPS), which is supplied to the each unit, is cut off. The cover-open sensing is operated
by the D23 of CPU.
In case, the red will be ON for informing the facts to user.
DC FAN / SOLENOID Driving
It is driven by transistor and controlled by D14(FAN MAIN), E16(FAN DUPLEX), C23(PICK-UP CLUTCH), C18(REGI
CLUTCH), D15(MPF CLUTCH) of CPU.
When it is high, the fan is driving by turning on the TR, and it is off when the sleep mode is selected. There are three
solenoids, and they are driven by paper pick-up, regi and MPF signal. It is turned on or off by C23, C18, D15 of CPU.
The diode protects the driving TR from the noise pulse, which is flown when the solenoid id de-energizing.
FAN Driving Circuit is driven by Transistor, and controlled by D14, E16 of CPU.
Service Manual
Product spec and feature
2-19
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