Dot-matrix printer diagnostics: On an impact (dot-matrix) printer, what common cause leads to a print pattern that alternates between light and dark (banding) across the page?

Introduction / Context:
Dot-matrix printers deposit ink by striking a fabric ribbon against paper. Consistency of ribbon movement is critical to maintain uniform ink density. “Light–dark” banding is often a ribbon feed issue rather than a head or paper motion problem.

Given Data / Assumptions:

• Symptoms: alternating light and dark horizontal bands across printed output.
• Printer type: impact/dot-matrix with fabric ribbon cartridge or spool.
• Mechanisms involved: ribbon feed, head impact, paper tractor feed.

Concept / Approach:

If the ribbon does not advance smoothly, the same section of ribbon is reused too frequently and becomes depleted (light), while a suddenly advanced segment appears darker. This creates a visible periodic variation in density independent of paper motion. Paper feed issues usually cause skewing, misregistration, or stretching patterns rather than neat alternating density bands.

Step-by-Step Solution:

Verification / Alternative check:

Swapping in a known-good ribbon that prints uniformly confirms the diagnosis. If banding persists, check head solenoids and platen pressure, but ribbon feed remains the prime suspect.

Why Other Options Are Wrong:

• Overheating print head: would cause dropout or stalling, not periodic dark/light bands.
• Misaligned head: leads to positional errors, not density oscillation.
• Erratic paper advancement: causes spacing errors or skew, not alternating ink density.

Common Pitfalls:

Overlooking worn ribbon drive gears; attempting platen pressure adjustments before verifying ribbon condition; using expired ribbons.

Final Answer:

Erratic ribbon advancement