Jams at the manual bypass (or multi-purpose) tray on the Konica Minolta bizhub C451 are among the most common service calls. This feed path is mechanically distinct from the main paper trays, utilizing a dedicated motor and a set of sensors to manage a single-sheet or small-batch feeding process. A persistent Jam code here requires a methodical diagnosis of its unique lifting, feeding, and sensing sequence to restore reliable operation for special media and quick prints.

Understanding the Jam Detection

The machine identifies a bypass misfeed through several precise conditions, offering clues to the specific failure point:

1. Primary Misfeed: The paper’s leading edge does not activate the Tray 1 Vertical Transport Sensor (PS4) within the required time after feeding starts. This indicates the paper never reached the merge point with the main paper path.
2. Paper Lift Failures:
   1. PS35 Limit Fault: The Bypass Paper Limit Sensor (PS35) is not blocked within a set time after the lift plate begins to rise to the feed position. This means the paper stack or the plate itself failed to reach the sensor.
   1. PS36 Lower Fault: For fed paper, the Bypass Paper Lower Sensor (PS36) is not blocked in time as the lift plate lowers after feeding. This indicates a problem with the paper’s exit from the lift area or the plate’s return motion.
3. Loop Registration Jam: The paper from the bypass does not form the necessary loop before reaching the timing rollers, causing a registration timing conflict. This often suggests a feed speed or synchronization issue.
4. TOD Permit Waiting Jam: A high-level timing fault where the “Top Of Document” signal is not enabled as expected, pointing to a control board communication error.

Relevant Components (Key Parts)

Focus your diagnosis on these bypass-specific and shared components:

• Bypass Paper Feed Motor (M27): The dedicated motor that drives the pickup and feed rollers, and often controls the lifting plate mechanism.
• Tray 1 Vertical Transport Sensor (PS4): The shared sensor where the bypass paper path merges with the main transport; the ultimate confirmation of successful feed.
• Bypass Paper Limit Sensor (PS35): Detects when the paper stack (or lift plate) is in the raised, ready-to-feed position.
• Bypass Paper Lower Sensor (PS36): Detects the paper’s leading edge as it begins to exit the bypass feed area.
• Paper Feed/Transport Drive Board (PFTDB): Controls M27 and monitors PS35 & PS36.
• Printer Control Board (PRCB): The main system controller.

Systematic Troubleshooting Procedure

Follow these steps sequentially to isolate the faulty component.

Step 1: Initial Mechanical Checks

• Open the bypass tray fully. Inspect the pickup roller and separation pad for severe wear, smoothness, or debris. Clean or replace them.
• Manually check the entire paper path from the tray entry to the merge point for obstructions, torn paper, or foreign objects.
• Ensure the paper lift plate moves smoothly up and down without binding. Check for worn bushings or broken gears in the lift mechanism.
• Verify you are using supported paper that is not curled, torn, or damp.

Step 2: Check Tray 1 Vertical Transport Sensor (PS4)

• Action: Perform an I/O check for PS4 in the service mode. This is a critical shared sensor; ensure it functions correctly.
• Physical Check: Inspect the sensor actuator for free movement. It is located where the bypass paper path joins the main vertical transport.
• Signal Verification: Confirm the signal at PFTDB connector CN4-8 toggles to ON when the sensor is blocked.

Step 3: Check Bypass Paper Limit Sensor (PS35)

• Action: Perform an I/O check for PS35. This sensor must be blocked when the lift plate is raised.
• Physical Check: Locate the sensor, typically near the lift plate’s top position. Ensure its actuator is engaged by the plate or paper stack.
• Signal Verification: Test the signal at PFTDB connector CN26<B>-10. It should be ON when the plate is up.

Step 4: Check Bypass Paper Lower Sensor (PS36)

• Action: Perform an I/O check for PS36. This sensor confirms initial paper pickup.
• Physical Check: Find this sensor along the initial feed path. Ensure its actuator moves freely.
• Signal Verification: The signal at PFTDB connector CN26<A>-11 should be ON when paper passes under the sensor.

Step 5: Check Bypass Paper Feed Motor (M27) Operation

• Action: Use the service mode to activate the dedicated bypass feed motor (M27).
• Observation: Listen and observe its operation. It should run smoothly to drive both the lift mechanism and the feed rollers. Erratic noise, stalling, or no movement indicates a faulty motor or severe mechanical binding.
• Control: The motor is driven via PFTDB connector CN26<B>, pins 1 through 4.

Step 6: Replace the Paper Feed/Transport Drive Board (PFTDB)

• If all three sensors (PS4, PS35, PS36) and motor M27 test correctly, the local controller (PFTDB) that drives them is likely defective. Replacement is the next step.

Step 7: Replace the Printer Control Board (PRCB)

• If the jam persists with a new PFTDB, the final step is to replace the main logic board (PRCB) to resolve any potential communication or high-level timing faults.

Conclusion

Troubleshooting a manual bypass jam on the bizhub C451 requires understanding its multi-sensor verification process. The key is to methodically verify each sensor in the sequence—PS35 (paper up), PS36 (paper picked), and finally PS4 (paper merged)—before testing the dedicated motor M27 and then the control boards. This logical progression from the point of origin (the lift plate) to the merge point ensures an accurate diagnosis, allowing you to efficiently resolve the misfeed and restore the functionality of this essential paper source.