Dot-matrix printer maintenance: During preventive maintenance, which component should you NOT lubricate in a dot-matrix (impact) printer?

Introduction / Context:
Dot-matrix printers use a print head with fine pins that strike an inked ribbon to form characters and graphics. Proper maintenance increases lifespan and print quality, but incorrect lubrication can cause severe damage or print defects.

Given Data / Assumptions:

• The printer is an impact (pin) printer.
• Preventive maintenance may include cleaning rails, belts, and light lubrication of approved moving parts.
• Manufacturer guidelines caution against lubricating sensitive mechanisms.

Concept / Approach:

Lubrication reduces friction in certain assemblies (carriage rails, gears) when the correct lubricant is used. However, the print head pins and their guide mechanism operate at high frequency and require precise, clean movement. Lubricants can attract dust and ink particles, gum up the guide tubes, and cause pin sticking or misfires, leading to poor print quality or head failure.

Step-by-Step Solution:

Verification / Alternative check:

After maintenance, the carriage should move smoothly and the print quality should be uniform. If pins stick or characters appear faint/misaligned, contamination or improper lubrication of the head may be the cause.

Why Other Options Are Wrong:

• Platen assembly: Some models permit minimal lubrication of the platen bearings, not the rubber surface, per guidelines.
• Print head pulley and paper advance gear bushings: Certain mechanisms may accept light lubrication per service docs.
• None of the above: Incorrect because there is at least one component (print head pins) that must not be lubricated.

Common Pitfalls:

Over-lubricating, using the wrong lubricant, contaminating the ribbon path, and touching the rubber platen with solvents that degrade it.

Final Answer:

Print head pins