Ricoh FT4460, Service Manual, Page: 341 / 413

28 February 1989
1.2 DIRTY BACKGROUND
- Phenomena -
1.
2 .
3 .
The background is dirty at image density level 4 (manual setting).
When newspapers are copied, the background is dirty even at level 7.
ADS copies have a dirty background.
- Possible Causes -
1.
2 .
3.
4.
5.
6.
Dirty optics
The optics fan brings in dust from outside the copier; this adheres to the
exposure glass and mirrors. Dirty optics can sometimes be detected by
increasing the magnification; this changes the position of the background
pattern. (For details, see the paragraph on uneven inage density.)
The following parts of the optics unit are most likely to become dirty:
(1) Toner shield glass (toner)
(2) Exposure glass and the mirrors 1 to 6.
Toner density is too high. (For details, refer to the troubleshooting
section.)
If the toner density is too high, toner scatters inside the copier, getting on
the toner shield glass, PTL, ID sensor, charge corona wire, and transfer
corona wire.
The mylar strips or the side seals have been stripped off the
development unit (side seals, inlet seals).
If seals have been damaged or removed, toner will scatter.
The exposure lamp intensity is too weak. This may be caused by
deterioration of the exposure lamp or low lamp regulator output voltage.
The doctor gap is too wide.
If the doctor gap is too wide (standard value: black toner: 0.6 + 0.1 mm),
the background will be dirty. With solid copies, the carrier may sometimes
adhere to the drum.
Defective or deteriorated drum
(1)
(2) The sensitivity of the drum is deteriorated.
The drum may not be properly grounded. The drum stay may be
deformed and as a result have a poor connection with the bearing on
the drum knob.
12-4