A dot-matrix printer produces alternating light and dark print density across a line. Which likely cause best explains this varying darkness pattern?

Introduction / Context:
Dot-matrix printers use an inked fabric ribbon advanced by a small mechanism as the print head moves. Uneven print density (light then dark, repeating) often points to consumable or feed issues. Knowing symptoms helps with fast, low-cost service.

Given Data / Assumptions:

• Pattern: Alternating light/dark density along the print direction.
• Print method: Impact pins strike an inked ribbon onto paper.
• Mechanisms involved: ribbon feed, head pressure, platen, paper feed.

Concept / Approach:
If the ribbon does not advance smoothly, the same section of fabric is struck repeatedly, depleting ink locally (light output). When the ribbon finally moves, a fresher ink area produces darker output—creating a light/dark periodic pattern. Paper thickness or head position cause overall density shifts, not regular alternation. Paper slippage tends to cause misalignment or skew, not periodic darkness bands.

Step-by-Step Solution:
Observe the repeating density pattern synchronized with head travel.Associate periodic density change with ribbon movement irregularities.Conclude that improper ribbon advancement best matches the symptom.

Verification / Alternative check:
Replacing or re-seating the ribbon cartridge and verifying the drive gear typically resolves the issue. A test with a new ribbon eliminates consumable variables.

Why Other Options Are Wrong:

• Paper slippage: Causes skew or gaps, not cyclical dark/light stripes.
• Paper thickness: Affects overall impact, not alternating bands.
• Head position: Misalignment affects clarity, not periodic density changes.
• None of the above: Incorrect because ribbon advance explains the pattern.

Common Pitfalls:
Overlooking a worn or jammed ribbon cartridge and spending time adjusting platen gap unnecessarily.

Final Answer:
Improper ribbon advancement