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Error code reference

Samsung Multifunction Printer Error Code #04-001

LSU Hsync error

Samsung codesSamsung multifunction printer codes

LSU Hsync error: after LD on, the laser beam detect signal is not generated or is irregular.

First step from the service manual

Check the Beam Detect signal. If there is a BD signal, replace the Main board. If not, check the LD control signal.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What #04-001 means on a Samsung multifunction printer

Error code #04-001 on a Samsung multifunction printer indicates a failure in the Laser Scanning Unit (LSU) Hsync (horizontal synchronization) detection circuit. Specifically, after the Laser Diode (LD) is powered on, the printer's control system fails to receive a valid Beam Detect (BD) signal, or the signal it receives is irregular. The BD signal is generated when the rotating polygon mirror sweeps the laser beam across the BD sensor at the start of each scan line. This timing signal is critical for synchronizing the laser firing sequence with the drum rotation, ensuring each line of the printed image is accurately positioned.

The diagnostic process for this error follows a clear branching logic. A technician must first determine whether a BD signal is present at all. If a BD signal is detectable but the error still triggers, the issue lies in how the Main board is interpreting or processing that signal, pointing to a failed Main board. If no BD signal is present, the investigation shifts upstream to the LD control signal itself, which may indicate a failed laser diode, a faulty LSU assembly, a broken wiring harness, or a defective connection between the LSU and the Main board.

Common root causes include a failed laser diode within the LSU, a seized or degraded polygon mirror motor preventing the mirror from spinning at the correct speed, a broken or intermittent connector between the LSU and the Main board, or Main board component failure affecting signal processing. Because the LSU is a precision optical assembly, physical contamination or damage to internal components can also disrupt the BD sensor's ability to register the laser sweep correctly.

Source: manufacturer service documentation.

Common causes of #04-001

  1. 01

    Failed or degraded Laser Diode (LD)

    Part replacement

    If the laser diode inside the LSU has burned out or weakened, the beam will not reach the BD sensor and no detect signal will be generated. This is confirmed by the absence of a BD signal during diagnostics.

  2. 02

    Faulty LSU assembly (polygon mirror motor failure)

    Part replacement

    If the polygon mirror motor inside the LSU is seized or rotating at an incorrect speed, the laser beam will not sweep across the BD sensor at the expected timing, producing no signal or an irregular one. The entire LSU assembly typically requires replacement in this scenario.

  3. 03

    Loose or damaged LSU wiring harness connector

    Wiring / connection

    A disconnected, corroded, or broken connector between the LSU and the Main board can interrupt both the LD control signal and the returning BD signal. Inspect all connector pins on both ends of the LSU cable for damage or poor seating.

  4. 04

    Failed Main board

    Part replacement

    If a BD signal is present at the LSU output but the error still triggers, the Main board is failing to correctly receive or process the signal. This is confirmed only after verifying that the BD signal exists using the diagnostic branch.

  5. 05

    Contaminated or obstructed BD sensor within the LSU

    Wiring / connection

    Toner dust or debris on the beam detect sensor inside the LSU can prevent the sensor from registering the laser sweep, producing an absent or intermittent BD signal even when the laser diode and mirror motor are functional.

See the test procedure for each cause

Frequently asked questions about #04-001

What does #04-001 mean on a Samsung multifunction_printer?
Error #04-001 is an LSU Hsync error, meaning the printer powered on its laser diode but did not receive a valid Beam Detect signal in return. This signal is required to synchronize each scan line during printing. The error indicates a problem somewhere in the laser scanning unit circuit, the wiring connecting it, or the Main board that processes the signal.
Can I fix error #04-001 myself or does it require a technician?
The first step any user can attempt is checking that all connectors to the LSU are firmly seated, as a loose cable can cause this error without any component failure. Beyond that, diagnosing whether a BD signal is present requires test equipment and technical knowledge, so most repairs beyond connector checks are best handled by a qualified technician. Replacing the LSU or Main board involves disassembling the printer and handling precision optical components.
Will resetting the printer clear error #04-001?
A power cycle or soft reset will not clear this error if an underlying hardware fault exists. The error will return as soon as the printer attempts to initialize the laser system and fails to detect the BD signal again. The root cause, whether a failed LSU, a bad connector, or a faulty Main board, must be resolved before the printer will operate normally.
Is it safe to continue using the printer with error #04-001 displayed?
The printer will typically halt operation when this error is active and will not allow print jobs to proceed, so there is no immediate safety hazard to the user. Continuing to attempt to force the printer to operate in this state is not recommended, as repeated failed startup cycles could stress related components. The printer should be serviced before returning to regular use.
How much does it cost to repair error #04-001 on a Samsung multifunction printer?
Repair costs depend on which component has failed. LSU assembly replacements typically range from moderate to high cost depending on the printer model, and Main board replacements can be significantly more expensive when factoring in parts and labor. For lower-cost printer models, the total repair cost may approach or exceed the replacement value of the unit, so it is worth getting a diagnostic estimate before authorizing any parts replacement.

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