SPO2 monitors

Nellcor A7390: troubleshooting and error codes

The ServiceForge knowledge base holds 27 documented symptoms for the Nellcor A7390, with 65 ranked causes, 24 diagnostic checks with test points and expected values, and 70 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

USB data port does not function properly

USB port fails to transfer data or communicate with PC

Ranked causes

1. USB cable not firmly connected (common)
2. Covidien bridge driver corrupted (occasional)
3. Mismatched baud rates between monitoring system and PC (occasional)
4. Mismatched COM port between PC and HyperTerminal (occasional)
5. USB port damaged (rare)
6. Main board failure (occasional)

6 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Questionable patient physiological measurements or missing/mistagged data patient safety

Unreliable SpO2 readings, patient data incorrectly tagged, or patient data missing

Ranked causes

1. Sensor not attached correctly (common)
2. Sensor is malfunctioning (occasional)
3. Electromagnetic interference (occasional)
4. Ambient light interfering with sensing (occasional)
5. Coin cell battery removed from main board (occasional)

5 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Date and time incorrect on LCD and in monitoring history download patient safety

System displays wrong date/time or monitoring history shows incorrect timestamps

Ranked causes

1. Date and time not set correctly during installation (common)
2. Coin cell battery depleted or removed and replaced (common)
3. Coin cell battery tab does not provide firm contact (occasional)
4. Main board failure (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Display does not function properly or looks distorted

LCD shows distorted image, improper display, or visual artifacts

Ranked causes

1. Electromagnetic interference (occasional)
2. LCD cable disconnected or improperly connected (common)
3. Main board is malfunctioning (occasional)
4. LCD visibly cracked or broken (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

No response when control buttons are pressed

Buttons do not respond to user input or commands

Ranked causes

1. Keypad ribbon cable not making contact (common)
2. System is frozen (occasional)
3. Buttons are defective (occasional)
4. Button activators on main board malfunctioning (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Sensor messages: SpO2 Pulse Search, Sensor Off, Cable/Sensor Disconnect, Signal Artifact patient safety

SpO2 sensor connectivity or signal quality issues indicated by monitor messages

Ranked causes

1. Sensor disconnected from cable or monitoring system (common)
2. Sensor detached from patient (common)
3. Interference from substances or motion (common)
4. Defective cable or sensor (occasional)

4 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

No sound during POST

Buzzer or speaker does not produce sound during power-on self-test

Ranked causes

1. Speaker cable is loose or disconnected (common)
2. Speaker is malfunctioning (occasional)
3. Main board is malfunctioning (occasional)

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit does not turn on when Power button is pressed

Monitoring system fails to power on despite pressing Power On/Off button

Ranked causes

1. Power button not held long enough (common)
2. Battery not properly seated (common)
3. Depleted or unsuitable battery (common)

First check

Verify power button activation

Test point: Power On/Off button
Expected: Button held for 1 second

3 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Audio alarm cannot be silenced patient safety

Alarm sound continues after pressing Silence button

Ranked causes

1. Main board is malfunctioning (occasional)
2. Keypad is damaged (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Audio alarm does not silence for specified time patient safety

Silence button press does not mute alarm for duration set in institutional defaults

Ranked causes

1. Institutional defaults not set correctly (common)
2. Silence Alarm button activator malfunction (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Blank display after normal POST

LCD screen shows no image or text following successful power-on self-test

Ranked causes

1. LCD cable disconnected (common)
2. LCD is damaged (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Low or critically low battery condition

Monitor displays low battery or critically low battery message

Ranked causes

1. Battery depleted after extended use (common)
2. Unsuitable battery type installed (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Monitoring system frozen

System is frozen or unresponsive

Ranked causes

1. NELL-1 malfunction requiring reset (common)
2. Main board malfunction (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Permission to Mute Alarm not functioning

User cannot mute alarm through Permission to Mute Alarm setting; alarm audio continues despite setting enabled

Ranked causes

1. Permission to Mute Alarm setting not enabled in Service Menu (common)
2. Alarm audio not disabled in Device Settings Sound Settings (common)

First check

Verify Permission to Mute Alarm is enabled

Test point: Service Menu Permission to Mute Alarm
Expected: Yes

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Pulse Volume not adjustable or not audible

Pulse tone does not sound with heartbeats or cannot be adjusted in volume

Ranked causes

1. Pulse Volume setting not configured correctly (common)
2. Sensor not connected properly or patient data not being detected (occasional)

First check

Access Pulse Volume setting

Test point: Device Settings Sound Settings Pulse Volume
Expected: menu accessible

2 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Screen Saver not activating or not darkening display

Screen does not darken during inactivity or Screen Saver setting not functioning

Ranked causes

1. Screen Saver Time setting not configured correctly (common)
2. Screen Saver only activates when no alarm condition and no buttons pressed (occasional)

First check

Access Screen Saver Time setting

Test point: Service Menu Power Saving Settings Screen Saver Time
Expected: setting accessible

1 more check with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Sensor Disconnect alarm not triggering or not at correct priority patient safety

Sensor disconnect is not detected or alarm priority does not match setting

Ranked causes

1. Sensor Disconnect alarm priority not set correctly (common)
2. Sensor not properly disconnected or connection is intermittent (occasional)

First check

Disconnect sensor from monitoring system

Test point: Sensor port connection
Expected: sensor fully disconnected, not making intermittent contact

2 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Sensor Off alarm not triggering or not at correct priority patient safety

Sensor off condition is not detected or alarm priority does not match setting

Ranked causes

1. Sensor Off alarm priority not set correctly (common)
2. Sensor still in contact with patient or connection not fully removed (occasional)

First check

Disconnect sensor from patient finger

Test point: Sensor contact with finger
Expected: sensor fully removed from finger

2 more checks with pass and fail actions, 2 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

System Failure (910) message displayed with buzzer sound

Monitor displays error code 910 and buzzer sounds during POST

Ranked causes

1. Speaker cable is disconnected (common)
2. Speaker or main board is malfunctioning (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

System Failure (920) message displayed

Monitoring system displays error message 920 after POST or abnormal shutdown

Ranked causes

1. Abnormally shut down or harnesses disconnected (common)
2. Batteries depleted (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

System failure message and error code appear on display

Monitor displays system failure message with associated error code

Ranked causes

1. Firmware is not loading correctly (occasional)
2. Monitoring system is malfunctioning (occasional)

2 corrective actions and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm Silenced function not working

Alarm silence button does not silence alarms; alarm tone continues or does not silence for expected duration

Ranked causes

1. Alarm Silence Duration not set to 30 seconds (common)

First check

Verify alarm silence duration setting

Test point: Service Menu Alarm Silence Duration
Expected: 30 seconds

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Alarm Volume Control not adjusting

Alarm volume cannot be adjusted or does not respond to volume control changes

Ranked causes

1. Alarm volume setting not accessible or responsive (occasional)

First check

Access Alarm Volume control

Test point: Device Settings Sound Settings Alarm Volume
Expected: menu accessible and responding to Up/Down buttons

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Display brightness cannot be adjusted

Screen brightness is too dim or too bright and does not respond to adjustment controls

Ranked causes

1. Brightness setting not accessible or not responding to controls (common)

First check

Access Brightness Setting

Test point: Device Settings Brightness Setting menu
Expected: menu accessible and responsive

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Key Beep Volume not responding

Key beep sounds on every button press when disabled, or does not sound when enabled

Ranked causes

1. Key Beep Volume setting not properly configured (common)

First check

Access Key Beep Volume setting

Test point: Device Settings Sound Settings Key Beep Volume
Expected: menu accessible

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Save Spot Reading function not working

Spot readings cannot be saved or saved data is not displayed in monitoring history

Ranked causes

1. Spot Reading not being saved or saved data cannot be retrieved (occasional)

First check

Attempt to save spot reading

Test point: Menu Save Spot Reading function
Expected: Spot Reading Saved message appears

1 more check with pass and fail actions, 1 corrective action, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Sensor Failure alarm not functioning patient safety

Sensor Failure condition is not detected or alarm does not sound

Ranked causes

1. Sensor Failure alarm priority setting not configured or sensor not actually failing (unknown)

First check

Verify Sensor Failure priority setting available

Test point: Service Menu Sensor Alarm Priority Settings
Expected: Sensor Failure option available with Low, Medium, or High selection

1 corrective action and part numbers are in ServiceForge. Connect ServiceForge to your AI

Error codes

Code	Meaning	Trigger	Severity
`001`	SpO2 front end RAM error	RAM memory failure detected in SpO2 front end	critical
`002`	SpO2 front end ROM/code integrity error	ROM or firmware code integrity check failed in SpO2 front end	critical
`004`	SpO2 front end reports command not allowed	Invalid or out-of-sequence command sent to SpO2 front end	error
`005`	SpO2 front end reports illegal value sent by SpO2 back end	Invalid parameter value received from SpO2 back end module	error
`006`	SpO2 front end reports calibration (offset) failure	Calibration offset calculation failed during initialization	error
`010`	Over-current limit in SpO2 front end has tripped	Overcurrent condition detected in SpO2 front end power supply	error
`012`	SpO2 front end reports other hardware problem	Unspecified hardware fault detected in SpO2 front end	error
`017`	SpO2 front end reports other hardware problem	Unspecified hardware fault detected in SpO2 front end	error
`018`	SpO2 front end reports internal register modified from expected value	Internal register value changed unexpectedly during operation	error
`048`	SpO2 front end reports spurious interrupt detected	Unexpected interrupt signal detected in SpO2 front end	warning
`050`	SpO2 front end reports internal software consistency check failed	Internal software checksum or integrity check failed in front end	error
`051`	SpO2 front end reports DigiCAL communications error	Communication error on DigiCAL interface of SpO2 front end	error
`256`	SpO2 back end reports beginning of packet missing	Packet received without proper start delimiter in back end	error
`257`	SpO2 back end reports packet state ID (SID) missing	Received packet missing State ID field in back end	error
`258`	SpO2 back end reports packet length error	Received packet length does not match expected value in back end	error
`259`	SpO2 back end reports message length error	Message length exceeds expected size or is invalid in back end	error
`260`	SpO2 back end reports packet contains unsupported Key	Packet received containing unrecognized Key field in back end	warning
`261`	SpO2 back end reports packet CRC error	Cyclic Redundancy Check failed on received packet in back end	error
`262`	SpO2 back end reports end of packet missing	Packet received without proper end delimiter in back end	error
`263`	SpO2 back end reports packet contains undefined Key	Packet received containing undefined Key field in back end	warning
`264`	SpO2 back end reports corrupted variable	Variable data integrity check failed in back end software	error
`265`	SpO2 back end reports memory overflow	Memory allocation exceeded available space in back end	error
`266`	SpO2 back end reports bad pointer	Invalid memory pointer detected in back end software	error
`267`	SpO2 back end reports parameter value out-of-range	Parameter value received outside valid range in back end	warning
`268`	SpO2 back end reports reset detected	Unexpected reset or restart detected in back end module	warning
`269`	SpO2 back end reports unexpected value	Unexpected data value received in back end processing	warning
`270`	SpO2 back end reports timeout	Operation exceeded timeout threshold in back end	warning
`271`	SpO2 back end reports not ready/not initialized	Back end module not initialized or ready for operation	error
`272`	SpO2 back end reports double fault	Multiple fault conditions detected simultaneously in back end	critical
`273`	SpO2 back end reports data out of range error	Measurement or data value outside acceptable range in back end	warning
`274`	SpO2 back end reports incompatible software version	Software version mismatch between modules in back end	error
`275`	SpO2 back end reports incorrect registration number	Registration or license number mismatch detected in back end	error
`276`	SpO2 back end reports sensor read failure	Unable to read sensor data in back end module	error
`277`	SpO2 back end reports sensor signature verification fails	Sensor authentication or signature check failed in back end	error
`280`	SpO2 back end reports does not support feature required by sensor	Sensor requires feature not supported by back end module	warning
`281`	SpO2 back end reports overflow/underflow	Data value overflow or underflow condition in back end processing	warning
`282`	SpO2 back end reports sensor activation failure	Sensor could not be activated during initialization in back end	error
`283`	SpO2 back end reports sensor write failure	Unable to write data to sensor in back end module	error
`284`	Host is providing both HW and SW ECG triggers	Both hardware and software ECG trigger signals sent to monitor	error
`285`	Host attempted Read or Close of Sensor Event before successful Open	Sensor Event accessed without proper initialization in host	error
`286`	Host attempted redundant Open of Sensor Event	Sensor Event opened multiple times without closing	error
`287`	An error occurred with the Sensor Event data and is unavailable for reading	Sensor Event data corrupted or unable to be accessed by host	error
`288`	No more Sensor Event data available for reading by host	All available Sensor Event data has been read by host	info
`289`	Sensor Private Label/Host Sensor Key incompatible; will not operate sensor	Sensor key does not match host requirements in back end	error
`512`	SpO2 back end reports internal software consistency check failed	Back end software checksum or integrity verification failed	error
`513`	SpO2 back end reports software functions executed before initialization completed	Software function called before initialization sequence complete	error
`514`	SpO2 back end reports internal memory buffer overflow	Internal memory buffer exceeded capacity in back end	error
`516`	SpO2 back end ROM/code integrity error	ROM or firmware code integrity check failed in back end	critical
`517`	SpO2 back end RAM error	RAM memory failure detected in back end module	critical
`518`	SpO2 back end reports internal software consistency check failed	Back end software checksum or integrity verification failed	error
`519`	SpO2 back end reports a state machine is in an unexpected state	Internal state machine detected in invalid state in back end	error
`520`	SpO2 back end reports memory corruption detected	Memory corruption detected by diagnostic check in back end	critical
`521`	SpO2 back end reports spurious interrupt detected	Unexpected interrupt signal detected in back end module	warning
`522`	SpO2 back end reports unable to issue commands to SpO2 front end	Communication failure when sending commands to front end	error
`523`	SpO2 back end reports unable to write to external Flash	External Flash memory write operation failed in back end	critical
`524`	SpO2 back end reports that communication with SpO2 front end lost	Communication link lost between back end and front end modules	critical
`525`	SpO2 back end reports internal register modified from expected value	Internal register value changed unexpectedly in back end	error
`701`	Flash writing transaction error	Error occurred during Flash memory write operation	error
`901`	SpO2 module communication error/setting value mismatch between host and SpO2 module	Communication error or configuration mismatch with SpO2 module	error
`902`	Program memory error	Error detected in program memory during operation	critical
`903`	RAM error	Error detected in RAM memory during operation	critical
`904`	PSRAM error	Error detected in PSRAM (pseudo-static RAM) during operation	critical
`905`	Sub MCU communication error	Communication failure with sub-microcontroller unit	error
`907`	RTC error	Real-time clock (RTC) error detected during operation	warning
`908`	Serial flash memory error	Error detected in serial Flash memory during operation	error
`909`	Internal voltage error	Internal power supply voltage out of acceptable range	warning
`910`	Sound/speaker error	Speaker or audio system malfunction detected during POST	warning
`912`	LCD error	LCD display malfunction detected during POST	warning
`913`	Button error	Button or keypad malfunction detected during POST	warning
`920`	Abnormally shut down last time	System was not shut down properly on previous startup	info

Likely causes and actions for each code are in ServiceForge. Connect ServiceForge to your AI

Community

0 fixes logged by technicians through their AI, with outcomes, for this model.

ServiceForge knowledge base record. Field-unverified unless technicians confirmed it. A teaching summary of the record, not a service manual. Export 2026-10-14.