Dot-matrix printer care: which part should never be lubricated during maintenance?

Introduction / Context:
Dot-matrix printers use an impact printhead with multiple tiny pins driven by solenoids to strike an ink ribbon. Proper lubrication keeps motion smooth, but lubrication of the wrong parts can destroy print quality and the mechanism itself.

Given Data / Assumptions:

• Standard dot-matrix printer with a multi-pin impact head.
• Manufacturer-recommended lubricants and schedules exist for rails and bearings.
• Printhead pins operate in precise bushings and must remain clean.

Concept / Approach:
Carriage rails and certain bearings may require approved, light lubrication to reduce friction. However, the printhead pins must never be lubricated. Oil attracts dust and ribbon debris, causing sticking pins, smeared characters, and misfires. Printheads are typically serviced by cleaning with approved solvents, not by applying oil or grease to the pins.

Step-by-Step Solution:

Verification / Alternative check:
After proper maintenance, the carriage glides smoothly and test patterns show crisp dots with no missing columns. Oiled pins often show fuzzy text and sticking columns.

Why Other Options Are Wrong:

• Carriage rails / bearings: Often require careful lubrication.
• Paper advance bearings: May receive lubrication per vendor guidance.
• None of the above: Incorrect because pins should not be lubricated.

Common Pitfalls:
Over-lubrication leading to oil migration onto the ribbon or paper path, and using non-approved oils that gum up over time.

Final Answer:
Printhead pins