Sensor Input Circuit; Paper Feeding; Paper Exit Sensing; Cover Open Sensing - Samsung ML-2251N/XAA Service Manual

Summary of Product
4.3.4 SDRAM
Used as Swath buffer, System working memory area, etc. when printing.
• Capacity: 16MByte (Export) / 32MByte (Domestic), expandable up to 144Mbyte (Export) /160MByte (Domestic)
• Optional Additional DIMM : 16MB / 32MB / 64MB /128MB
• Type : SDRAM 100MHz/133MHz , 16bit

4.3.5 Sensor Input Circuit

4.3.5.1. Paper Empty Sensing
The Paper Empty sensor (Photo Interrupter) on the engine board is monitored by the CPU. When the cassette is
empty the printer flashes the red ERROR LED.
4.3.5.2. MP Sensing
Presence of paper in the MP tray is detected by operation of the MP Sensor (Photo Interrupter) on the frame. The
CPU monitors this sensor to recognize paper in the MP, and paper is fed from MP if there is paper present.

4.3.5.3. Paper Feeding

When paper passes the actuator on the feed sensor, it is detected by the Photo interrupter. This is monitored by
the CPU and this signal starts the process of creating the image after a certain delay time.
If the feed sensor is not detected within 1 sec. after paper is fed, a paper jam0 occurs. (Red ERROR LED is lit).
4.3.5.4. Toner Remain Sensing
The ML2250 does not have a toner sensor fitted

4.3.5.5. Paper Exit Sensing

This detects that paper exits cleanly from the set using an exit sensor on the engine board and actuator on the frame.
The CPU detects the on/off time of the exit sensor and normal operation or jam status is reported.
If a Jam 2 error occurs the Red ERROR LED is lit.

4.3.5.6. Cover Open Sensing

The Cover open sensor is located on the power supply board. It is operated by a molded tab on the front cover.
When the front cover is open the +24V and +5V supplies to the DC fan, solenoid, main motor, polygon motor part
of LSU,
HVPS and LSU Laser diode are cut off.
4.3.5.7. DC FAN/Solenoid Driving Circuit
A fan driving circuit is controlled by the CPU via a transistor. It is automatically turned off when a machine enters
sleep mode.
There are two solenoids, these are driven by signals from the CPU (MP and paper pick-up).
4.3.5.8. Motor Driving Circuit
The main motor drives the paper feed, developing unit, Fuser and Exit ass'y. It is driven by software which controls
the acceleration, constant speed and deceleration profiles. The Motor is driven using an A3977 driver IC.
Service Manual
4-12
Samsung Electronics