Samsung SCX-4720F Service Manual page 40

Summary of Product
4.4.1 HVPS(High Voltage Power Supply)
1) Transfer High Voltage (THV+)
- Function : It is this voltage that transfers toner from the OPC Drum to the paper.
- Output voltage : +1300V DC±20V
- Error : IF THV (+) is not present, low density printing occurs due to toner on the OPC Drum not being
transferred to the paper. It is possible that waste toner over-flow can occur if this condition
persists. Ghost images may appear which repeat at 76mm intervals.
2) Charge Voltage (MHV)
- Function : It is this voltage that charges the surface of the OPC to -900V ~ -1000V.
- Output voltage : -1550V DC ± 50V
- Error : IF MHV is not present toner then since the OPC drum surface has no charge toner is attracted to
the whole OPC surface. A black page is printed out when this happens.
3)Cleaning Voltage (THV-)
- Function : It removes toner contamination from the rear side of the paper by sending (-) polarity to the
transfer roller forcing toner to transfer back to the to OPC drum.
- Output Voltage : -1200V, +300V/-150V
- Error : Smudges and toner contamination on the reverse side of the printed page.
4) Developing Voltage (DEV)
- Function: It is this voltage that develops toner with on to the section of the OPC drum surface exposed
by the LSU
(Laser Scanning Unit).
* When printing the exposed voltage on the OPC is -180V, unexposed is -900~-1000V, and the exposing
voltage on the DEV is -430V. Therefore toner with (-) polarity is developed onto an exposed
section of the OPC.
- Output voltage: -430V DC ± 20V
- Error: a) If DEV is GND, print density gets extremely low.
b) When DEV is floating due to poor connection between the frame and cartridge contacts etc.,
print density gets extremely high.
5) Supply Voltage (SUP)
- Function: It is this voltage that supplies toner to the developing roller.
- Output voltage: : -580V DC ± 50V (Use ZENER, DEV Gear)
- Error: a) When SUP is GND print density gets extremely low.
b) If SUP is floating due to poor connection between the frame and cartridge contacts etc. density
gets extremely low such that it is hard to see toner with the eyes
6) OPC Ground ZENER Voltage
- Function: It is this voltage that prevents image contamination under low temperature and low humidity
environment conditions.
- When a set prints without an output voltage, -130V DC ± 15V is maintained on OPC ground. (-103V
ZENER diode is connected to OPC ground)
- Error type: a) When the ZENER diode is - 0V there is no serious image problem in general environ-
Service Manual
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ment, but in low temperature and low humidity environments it is possible that contamination
can occur on the entire image
b) When the ZENER diode is disconnected a blank page is printed out. (It is the same when
a ZENER diode is disconnected from OPC ground.)
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