Identifying and Resolving Laser Printing Issues on Brother MFC-9140CDN

If you're encountering streaking, botchy, or smudgy black prints on your Brother MFC-9140CDN laser printer, fret not. In this guide, we'll delve into troubleshooting steps to pinpoint the problematic part and effectively resolve the issue.

Assessing the Situation

Upon receiving the printer, you noticed streaking issues specifically with black printing. While all cartridges are remanufactured and hold over 40% toner, the problem persists. Initially, the test page printed fine (PDF number 1), but subsequent prints exhibited the aforementioned issues (PDF number 2). Despite thorough maintenance, including cleaning corona wires, drums, LED heads, and high voltage contacts, the problem persisted (PDF number 3).

Analyzing Test Results

To isolate the issue, you performed a cartridge test print (PDF number 4), which revealed that swapping the black unit with the magenta resulted in normal black printing, indicating that the black toner and drum unit are operational. Additionally, the transfer belt and fuse unit were deemed functional.

Potential Causes and Solutions

1. LED Head or Power Supply Issue: Given that the black print degrades over time, suspicion falls on the LED head or power supply. Check if the LED head has malfunctioned or if the power supply to the corona wires of the black unit is insufficient. This may involve inspecting the low voltage board for LED head issues or the high voltage board for power supply problems.
2. Capacitor or Corona Wire Issue: Consider the possibility of capacitor failure on the board causing degradation over time. Additionally, ensure the corona wire for the black unit in the transfer belt is intact and properly charged.

Troubleshooting Steps

1. LED Head Inspection: Examine the LED head for any signs of damage or malfunction. Replace if necessary.
2. Power Supply Assessment: Test the power supply to ensure it's providing sufficient voltage to the corona wires. Replace the low or high voltage board if faulty.
3. Capacitor Check: Inspect capacitors on the board for any bulging or leaking. Replace damaged capacitors as they may be causing degradation issues.
4. Corona Wire Verification: Confirm the integrity and charge of the corona wire for the black unit in the transfer belt. Clean or replace if necessary.

By following these systematic troubleshooting steps, you can effectively identify and resolve laser printing issues on your Brother MFC-9140CDN printer. Remember to carefully inspect each component and systematically rule out potential causes until the problem is resolved.

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