Laser printing process (conditioning step): During the conditioning phase of a laser printer, a uniform charge of what magnitude and polarity is placed on the photosensitive drum?

Introduction / Context:
Laser printers form images using electro-photography. A key step is conditioning (primary charging), where the drum receives a uniform electrostatic charge to prepare it for exposure by the laser. Knowing the typical charge level and polarity helps diagnose print defects such as backgrounding or light prints.

Given Data / Assumptions:

• The printer uses a standard organic photoconductor (OPC) drum.
• A primary charge is applied by a corona wire or primary charge roller (PCR).
• We seek the typical magnitude and polarity used in many engines.

Concept / Approach:

Most laser printers bias the drum to a negative potential before laser exposure. Common targets are around -600 V (model-dependent). This uniform negative charge is selectively discharged by the laser to form the latent image. Positive values such as +600 V are atypical for common office printers, and low values like +12 V are far below operational requirements.

Step-by-Step Solution:

Verification / Alternative check:

Service manuals specify PCR bias values; measuring with high-voltage probes or reading diagnostic logs confirms the operating range. Print-quality symptoms often correlate with improper drum bias.

Why Other Options Are Wrong:

• +1000 volt / +600 volts: Incorrect polarity for typical systems.
• -1000 volts: Possible in some designs, but -600 V is the commonly cited standard value in many office printers.
• +12 volts: Far too low for drum conditioning.

Common Pitfalls:

Confusing developer bias, transfer bias, and drum bias; overlooking that exact values vary by model; assuming corona-wire systems when a PCR is used.

Final Answer:

-600 volts