HP LaserJet M750dn Color Enterprise

The heartbeat LED provides information about product operation. If a product error occurs, the formatter displays a message on the control-panel display. However, error situations can occur causing the formatterto- control panel communication to be interrupted.

NOTE: HP recommends fully troubleshooting the formatter and control panel before replacing either assembly. Use the heartbeat LED to troubleshoot formatter and control panel errors to avoid unnecessarily replacing these assemblies

Formatter-to-control panel communication interruptions

• The firmware does not fully initialize and configure the control panel interface.
• The control panel is not functioning (either a failed assembly or power problem).
• Interface cabling between the formatter and control panel is damaged or disconnected.

TIP: If the heartbeat LED is illuminated—by an error condition or normal operation—the formatter is fully seated and the power is on. The pins for the LED circuit in the formatter connector are recessed so that this LED will not illuminate unless the formatter is fully seated.

The heartbeat LED operates according to the product state. When the product is initializing, see Heartbeat LED, product initialization. When the product is in Ready mode, see Heartbeat LED, product operational.

Heartbeat LED, product initialization

The following table describes the heartbeat LED operation while the product is executing the firmware boot process.

NOTE: When the initialization process completes, the heartbeat LED should be illuminated solid green.

If after initialization, the heartbeat LED is not solid green, see Heartbeat LED, product operational.

Product initializing state	Heartbeat LED, normal state	Heartbeat LED, error state
No power (power cable disconnected or power switch off)	Off	Not applicable
Power on (immediately after the power switch pressed)	Red, solid • Duration should be 1 second or less	Red, solid Firmware error; problem finding hardware and booting the serial peripheral interface flash memory • Boot process halted Replace the formatter.
Serial peripheral interface (SPI) flash memory boot	Green, solid	Red, solid Firmware error; problem corrupt or missing SPI flash memory • Boot process halted Replace the formatter.
HW checks on board DRAM	Green, solid	Red, solid Power on self check failure ◦ Boot process halted Replace the formatter.
Control panel connection initializes	Green, solid NOTE: Control panel communication successful. If an error occurs, a message will appear on the control-panel display.	Yellow, fast flash Formatter to control panel connection failed ◦ Boot process continues Check the cables between the formatter and control panel for damage. Make sure that the cables are fully seated.
Preboot menu available (including diagnostics)	Green, solid	Red, solid Diagnostic failure ◦ Follow diagnostic instructions Turn the power off, and then on again to restart the initialization process.
Accessing disk for firmware image	Green, solid NOTE: If applicable, disk error messages appear on the control-panel display.	Yellow, fast flash Control panel not connected
Firmware boot	Green, solid NOTE: If applicable, error messages appear on the control-panel display.	Yellow, fast flash Control panel not connected
Product operational	Green, heartbeat blink NOTE: If applicable, error messages appear on the control-panel display.	Yellow, fast flash Control panel not connected
49.XX.YY error or initialization freezes	Not applicable	LED off NOTE: An error message (for example, 49.XX.YY) might appear on the control-panel display.Eventually a formatter connection missing message will appear. Turn the power off, and then on again to restart the initialization process. If the error persists, perform a firmware upgrade.
Control panel connection interrupted after the product is operatio	Not applicable	Yellow, fast flash Control panel not connected
Sleep Mode	Green, slow blink	Not applicable
Approaching Sleep Mode	Green, slow blink	Not applicable
Wake up from Sleep Mode	Follows initialization progression	Follows initialization progression
Approaching wake up from Sleep Mode	Follows initialization progression	Follows initialization progression