Development Bias - Gestetner A193 Service Manual

PCU (PHOTOCONDUCTOR UNIT)

4.5.4 Development Bias

[A]
[C]
[B]
A193D534.wmf
This machine uses a negative-positive development system (write to black),
in which the black areas of the latent image are at a low negative charge
(-140 ± 50 V) and white areas are at a high negative charge (-900 V).
To transfer negatively charged toner to the black areas of the latent image on
the drum, the high voltage supply board [A] applies a bias of -600 volts to the
development rollers throughout the image development process. The bias is
applied to the development roller shaft [B] through that shaft's gear [C].
The development bias is kept at 0V until the latent image on the drum comes
to the development roller. This is to prevent toner from transferring to the
area of drum near the development roller, which has not yet been charged.
The development bias is then increased to -600 V at the same time as the
development clutch turns on.
The development bias voltage (-600 V) can be adjusted using the service
program mode, SP2-201.
SM 2-33 (A193)