Pulse oximeters

Nellcor N-600: troubleshooting and error codes

The ServiceForge knowledge base holds 16 documented symptoms for the Nellcor N-600, with 36 ranked causes, 8 diagnostic checks with test points and expected values, and 155 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Alarm does not sound high voltage

No alarm tone when alert condition occurs

Ranked causes

1. Alarm silenced (common)
2. Speaker connection loose (common)
3. Speaker defective (occasional)
4. Main Board PCB defective (occasional)

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

Low Battery indicator lights on AC power

Low battery indicator illuminates steadily while connected to AC outlet with adequate charge

Ranked causes

1. Blown or open fuse in Power Entry Module (common)
2. Defective power supply (occasional)
3. Battery defective or aged (occasional)
4. Loose or corroded harness connection on Main Board (occasional)

First check

Verify unit plugged into operational AC outlet

Expected: AC indicator lit

1 more check with pass and fail actions, 4 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Battery does not charge

Battery fails to accept charge when connected to AC power

Ranked causes

1. Battery aged over 2 years (common)
2. Battery defective (common)
3. Defective power supply (occasional)

First check

Verify charging voltage on new battery

Test point: Battery terminals while on AC power
Expected: 7.05-7.35 volts initial climb, then decrease with time V, +0.30 -0.15 V

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

Display pixels do not light

Display screen shows no illuminated pixels

Ranked causes

1. Connection issue between Main and Display PCB (common)
2. Display PCB defective (occasional)
3. Main Board PCB defective (occasional)

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

Display values missing or erratic

Display shows missing data or values fluctuate erratically

Ranked causes

1. OXIMAX sensor issue (common)
2. OXIMAX sensor defective (common)
3. Main Board PCB defective (occasional)

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

No printout received from data port

Monitor fails to send data to connected printer via data port

Ranked causes

1. Printer not operational (common)
2. Baud rate mismatch between monitor and printer (common)
3. Main Board PCB defective (occasional)

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

SpO2 or Pulse values change rapidly with erratic amplitude patient safety

Measured values fluctuate rapidly; Pulse Amplitude indicator shows erratic behavior

Ranked causes

1. OXIMAX sensor damp or reused excessively (common)
2. Electrosurgical unit interference (occasional)
3. Main Board PCB defective (occasional)

First check

Verify performance per Performance Verification procedure

Expected: Normal SpO2 and Pulse values within expected range

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

Alarm sounds without apparent reason

Alarm generates unexpectedly with no apparent trigger

Ranked causes

1. Moisture or liquid contamination (common)
2. Main Board PCB defective (occasional)

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

Buttons do not respond

Monitor does not respond when buttons are pressed while powered on

Ranked causes

1. Main Board PCB defective (common)
2. Top enclosure assembly defective (occasional)

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

Pulse Amplitude indicator shows pulse but displays zero patient safety

Pulse Amplitude indicator responds to patient signal but SpO2/Pulse values show zero

Ranked causes

1. OXIMAX sensor damaged (common)
2. Main Board PCB defective (occasional)

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

RS-232 nurse call inoperable

Nurse call signal over RS-232 interface not functioning

Ranked causes

1. Connection issue on data port (common)
2. Main Board PCB defective (occasional)

First check

Measure voltage between pins 5 and 11 of data port

Test point: Data port pins 5 (GND) and 11 (nurse call)
Expected: -5 to -12 VDC during normal operation; +5 to +12 VDC during alarm, +3.5 -3.5 V (no alarm)
Tools: DC Voltmeter

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

Display PCB requires replacement caution

Display PCB removal and reinstallation procedure for monitor maintenance or repair

Ranked causes

1. Display PCB damaged or defective (unknown)

First check

Verify CCFL harness disconnected from J4 on Main Board PCB

Test point: J4
Expected: CCFL harness removed

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

Error code on disconnect from AC

Unit generates error code when powered from battery after AC disconnection

Ranked causes

1. Battery discharged or defective (common)

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

Low Battery alarm during DC operation

Low Battery indicator illuminates and alarm sounds during battery-powered operation

Ranked causes

1. Battery nearing depletion (common)

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

Primary speaker fails with high-pitched tone

Primary speaker failure resulting in slow, high-pitched audible tone

Ranked causes

1. Primary speaker malfunction (common)

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

Primary speaker failure detected

Monitor displays 'PRIMARY SPKR FAILURE: NOTIFY SVC PERSONNEL' message with high-pitched, slow-pulsing piezo tone. Once silenced, tone repeats every three minutes.

Ranked causes

1. Primary speaker hardware failure (common)

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

Error codes

Code	Meaning	Trigger	Severity
`1`	%SpO2 front end RAM error	RAM error detected during operation	error
`10`	Over-current limit in %SpO2 front end has tripped	Current draw exceeds maximum threshold	error
`11`	%SpO2 front end reports incorrect system voltage	Supply voltage outside acceptable range	error
`12`	%SpO2 front end reports other hardware problem	Unspecified hardware failure detected	error
`14`	%SpO2 front end reports communication channel overflow	Receive buffer overflows during message reception	warning
`16`	%SpO2 front end reports watch dog time out	Watchdog timer expires; front end does not respond within timeout period	critical
`17`	%SpO2 front end reports that sensor appears defective	Sensor communication fails or sensor reports invalid data	error
`18`	%SpO2 front end reports internal register appears modified from expected value	Register verification detects unexpected value change	error
`19`	%SpO2 front end reports signal out-of-range	Sensor signal amplitude or frequency outside valid range	warning
`2`	%SpO2 front end ROM/code integrity error	ROM code checksum or integrity verification fails	error
`256`	%SpO2 back end reports beginning of packet missing	Packet start marker not found in expected location	error
`257`	%SpO2 back end reports packet start ID (SID) missing	Start ID field not found in packet header	error
`258`	%SpO2 back end reports packet length error	Declared packet length does not match actual received length	error
`259`	%SpO2 back end reports message length error	Message length field invalid or inconsistent	error
`260`	%SpO2 back end reports packet contains unsupported key	Packet contains a command or key not recognized by back end	warning
`261`	%SpO2 back end reports packet CRC error	Packet checksum does not match calculated CRC	error
`262`	%SpO2 back end reports end of packet missing	Packet terminator not found where expected	error
`263`	%SpO2 back end reports packet contains undefined key	Packet contains unknown command or identifier	warning
`264`	%SpO2 back end reports corrupted variable	Variable value fails integrity check or is out of range	error
`265`	%SpO2 back end reports memory overflow	Memory allocation request exceeds available space	error
`266`	%SpO2 back end reports bad pointer	Invalid pointer value detected during dereference	error
`267`	%SpO2 back end reports parameter value out-of-range	Parameter value exceeds valid bounds	warning
`268`	%SpO2 back end reports reset detected	Unexpected system reset or reboot detected during operation	warning
`269`	%SpO2 back end reports unexpected value	Received value does not match expected result or range	warning
`270`	%SpO2 back end reports time-out	Operation does not complete within timeout period	error
`271`	%SpO2 back end reports not ready/not initialized	Module or subsystem not yet initialized when accessed	error
`272`	%SpO2 back end reports double fault	Two faults detected simultaneously or fault during fault handling	critical
`273`	%SpO2 back end reports date out-of-range error	Date value is invalid or outside acceptable range	warning
`274`	%SpO2 back end reports incompatible software version	Software component version mismatch detected	error
`275`	%SpO2 back end reports incorrect registration number	Registration or license number verification fails	warning
`276`	%SpO2 back end reports sensor read failure	Unable to read sensor data or sensor communication fails	error
`277`	%SpO2 back end reports sensor signature verification fails	Sensor identification or authentication check fails	error
`278`	%SpO2 back end reports warmed sensor temperature set point failure	Temperature control for warmed sensor cannot reach or maintain setpoint	error
`279`	%SpO2 back end reports warmed sensor / %SpO2 front end incompatible	Warmed sensor and front end firmware/hardware versions do not match	error
`280`	%SpO2 back end reports does not support feature required by sensor	Sensor requires a feature not implemented in current firmware	warning
`281`	%SpO2 back end reports overflow/underflow	Numerical value exceeds maximum or falls below minimum	error
`282`	%SpO2 back end reports sensor activation failure	Sensor cannot be activated or powered on	error
`283`	%SpO2 back end reports sensor write failure	Unable to write configuration or data to sensor	error
`284`	ECG trigger error	ECG trigger signal absent, invalid, or out of range	error
`285`	Sensor trend not open	Request to access sensor trend data but trend not opened	warning
`286`	Sensor trend already open	Attempt to open trend data that is already open	warning
`287`	Sensor trend data unavailable	Trend data requested but not available or accessible	warning
`288`	All sensor trend data read	All available trend data has been read; end of trend reached	info
`289`	Incompatible private label	Private label configuration mismatch or unsupported variant	warning
`3`	%SpO2 front end reported bad Cyclic Redundancy Check (CRC)	CRC check fails during data transmission or storage verification	error
`4`	%SpO2 front end reported FSP message not allowed	Illegal FSP message received by front end	warning
`48`	%SpO2 front end reports spurious interrupt	Unexpected interrupt asserted to front end CPU	warning
`49`	%SpO2 front end reports internal buffer overflow	Internal message buffer exceeds capacity	error
`5`	%SpO2 front end reported illegal value sent in FSP message	Out-of-range or invalid parameter value in FSP message	warning
`50`	%SpO2 front end reports intermittent error	Intermittent failure detected during operation	warning
`51`	%SpO2 front end reports digital communications error	Communication protocol error or checksum failure	error
`512`	General failure of UIF Module generic post or Dead battery/Missing battery	UIF module POST fails or battery missing/disconnected	critical
`514`	Real time clock is non-operational	RTC fails to respond or is not functioning	error
`515`	Application code is not present in the Flash	Flash memory does not contain valid application code	critical
`516`	Invalid Flash type	Flash memory type does not match expected configuration	critical
`517`	Serial clock line is not toggling or is toggling at an incorrect rate	Serial clock signal missing or frequency incorrect	critical
`518`	Application program is corrupt	Application code CRC check fails	critical
`519`	Invalid Nell-1A version	Nell-1A firmware version not recognized or too old	error
`52`	%SpO2 front end reports warmer error	Warmer/heater control failure or temperature sensor error	error
`520`	Error in the start up sequence	Startup initialization fails at some point	critical
`521`	OS multi-tasking service failure	Real-time operating system fails to manage tasks	critical
`522`	A state machine has received an unknown state transition	State machine receives unexpected or invalid transition	error
`523`	The operation just attempted was not completed successfully - for example, Institutional Defaults could not be reset	Requested operation fails to complete or returns error	error
`524`	An unexpected value was received - for example, an out-of-range parameter was passed to a function	Received value outside valid range or not as expected	warning
`525`	EEPROM CRC failure	EEPROM checksum verification fails	error
`526`	%SpO2 module not responded	No response from %SpO2 module within timeout period	critical
`527`	Institutional parameters lost - e.g. for UIF: Institutional EEPROM section CRC corrupt	Institutional parameters cannot be read or CRC fails	error
`528`	Current settings lost - e.g. for UIF: Institutional EEPROM section CRC corrupt	Current settings data is corrupted or cannot be read	error
`529`	Critical low battery	Battery voltage drops below critical threshold	critical
`53`	Front end data not received	No data packet received from front end within timeout period	critical
`530`	Low battery error	Battery voltage drops below normal operating threshold	warning
`531`	External watchdog failure	External watchdog timer fails to function	critical
`532`	Power PC watchdog failure	PowerPC watchdog timer fails or does not reset	critical
`533`	Boot NVROM uninitialized error	Boot ROM/NVRAM is not properly initialized	critical
`534`	Failed CRC check of application code in flash	Application code in flash fails CRC verification	critical
`535`	Failed periodic ram CRC check on application code running in RAM	Running application code fails CRC check periodically	critical
`560`	Memory corruption detected	Memory integrity check detects corruption	error
`561`	RTOS Resource unavailable	Real-time OS resource (semaphore, queue, etc.) not available	error
`562`	%SpO2 front end reset	%SpO2 front end has reset or rebooted unexpectedly	warning
`563`	%SpO2 reported error	%SpO2 module reports an error condition	error
`564`	Clinical mode was exited after input was received	Clinical mode exits unexpectedly after receiving input	warning
`565`	Communication failures between software modules	Inter-module communication fails or times out	error
`566`	Excessive resets before UIF runs	System resets repeatedly before UIF module starts	critical
`567`	An unexpected interrupt has been asserted	Interrupt occurs when none was expected	warning
`568`	General failure in UIF module generic post	UIF module power-on self-test fails	critical
`569`	BOOT application program is corrupt - CRC does not match	Boot loader code fails CRC verification	critical
`570`	RTC was restarted	Real-time clock has been restarted or lost time	info
`574`	Excessive restarts within one minute	System restarts too many times in a short time period	critical
`575`	Trend data corrupted	Trend data fails integrity check	warning
`576`	Logic Processing Board (LPS) is going through excessive resets	LPS module resets repeatedly	error
`577`	LPS status messages not arriving in a timely manner	LPS communication lags or status messages delayed	warning
`578`	LPS driver has received too many corrupt (protocol error) messages	LPS driver detects excessive protocol errors from LPS	error
`579`	Status report AC OK bit does not equal the hardware AC OK signal	Software AC status does not match hardware signal	warning
`580`	LPS driver received only a partial LPS message	LPS message reception incomplete or truncated	error
`581`	Too many corrupt (invalid data) message	Excessive number of messages with invalid data received	error
`582`	Unable to enter shelf-mode, this could mean that the LPS is dead or there is a serial port transmit problem	Shelf mode transition fails	critical
`583`	Primary speaker failure detected	Speaker does not respond or test fails	warning
`6`	%SpO2 front end reports calibration (offset) failure	Calibration or offset adjustment fails during startup or operation	error
`650`	Oximetry module reports internal software consistency check failed	Oximetry module software integrity verification fails	error
`651`	Oximetry module reports software functions executed before initialization completed	Oximetry function called before module ready	error
`652`	Oximetry module reports internal memory buffer overflow	Oximetry module internal buffer exceeds capacity	error
`653`	Oximetry module reports host reset	Oximetry module detected unexpected host reset	warning
`654`	Oximetry module ROM/Code integrity error	Oximetry module firmware fails integrity check	error
`655`	Oximetry module RAM error	Oximetry module RAM test fails	error
`656`	Oximetry module reports background self-test failed to complete in the allocated time	Oximetry self-test does not finish within timeout	warning
`657`	Oximetry module reports a state machine is in an unexpected state	Oximetry state machine in invalid state	error
`658`	Oximetry module reports memory corruption detected	Oximetry module memory integrity check fails	error
`659`	Oximetry module reports spurious interrupt detected	Oximetry module receives unexpected interrupt	warning
`660`	Oximetry module reports unable to issue commands to %SpO2 front end	Oximetry cannot communicate with %SpO2 front end	error
`661`	Oximetry module reports unable to write to external Flash	Oximetry cannot write data to external flash memory	error
`662`	Oximetry module reports communication with %SpO2 front end lost	Oximetry loses communication with %SpO2 front end	critical
`663`	Oximetry module reports internal register modified from expected value	Register verification detects unexpected value change	error
`701`	POST external hardware failsafe circuit error	External hardware failsafe circuit test fails	critical
`702`	POST PWR_ENA fail	Power enable circuit test fails during POST	critical
`703`	Unknown state machine # or charge state	Invalid state machine number or charge state detected	error
`704`	Unexpected interrupt	Interrupt asserted when none expected	warning
`705`	Stack over/under error	Stack pointer exceeds bounds or underflows	error
`706`	ROM CRC error - POST or background	ROM code fails checksum verification	critical
`707`	POST RAM error	RAM test fails during power-on self-test	critical
`708`	Unexpected reset	System resets unexpectedly during operation	error
`709`	Unexpected internal WD instance #1	Internal watchdog #1 times out unexpectedly	error
`710`	Unexpected internal WD instance #2	Internal watchdog #2 times out unexpectedly	error
`711`	Unexpected internal WD instance #3	Internal watchdog #3 times out unexpectedly	error
`712`	Unexpected internal WD instance #4	Internal watchdog #4 times out unexpectedly	error
`713`	Unexpected internal WD instance #5	Internal watchdog #5 times out unexpectedly	error
`714`	Unexpected internal WD instance #6	Internal watchdog #6 times out unexpectedly	error
`715`	LINE_V & AC_OK disagree	AC line voltage and AC_OK signal mismatch	warning
`716`	POST Internal WD circuit error	Internal watchdog circuit test fails during POST	critical
`717`	Battery shorted with AC power	Battery and AC power connected simultaneously	critical
`718`	Battery open with AC power	Battery disconnected or missing when AC power present	critical
`719`	EEPROM W/R failure - POST or background	EEPROM write or read operation fails	error
`720`	Battery charger error - instance #1	First battery charger circuit fails	error
`721`	Battery charger error - instance #2	Second battery charger circuit fails	error
`722`	Battery charger error - instance #3	Third battery charger circuit fails	error
`723`	Battery charger error - instance #4	Fourth battery charger circuit fails	error
`724`	Battery charger error - instance #5	Fifth battery charger circuit fails	error
`725`	Battery charger error - instance #6	Sixth battery charger circuit fails	error
`726`	Battery charger error - instance #7	Seventh battery charger circuit fails	error
`727`	Battery charger error - instance #8	Eighth battery charger circuit fails	error
`728`	Battery charger error - instance #9	Ninth battery charger circuit fails	error
`729`	Battery critical without AC power	Battery voltage critical and no AC power available	critical
`730`	Battery fail without AC power	Battery failure detected with no AC power backup	critical
`731`	EEPROM CRC Error - EEPROM cleared	EEPROM checksum fails and contents automatically cleared	error
`732`	Vref error on DC	DC voltage reference circuit fails or out of spec	error
`733`	Vref error on AC	AC voltage reference circuit fails or out of spec	error
`734`	Overtemperature (> 58 C)	Internal temperature exceeds 58°C threshold	critical
`735`	Battery I charge	Battery charging current measurement error or out of spec	error
`736`	Battery I discharge	Battery discharge current measurement error or out of spec	error
`737`	Temperature low	Internal temperature drops below minimum operating threshold	warning
`738`	Hardware failsafe occurred, maybe overtemperature	Hardware safety circuit activates, possibly due to overtemperature	critical
`739`	Hardware failsafe occurred, maybe overcurrent	Hardware safety circuit activates, possibly due to overcurrent	critical
`740`	Hardware failsafe occurred, cause unknown	Hardware safety circuit activates for unknown reason	critical
`741`	Message RX CRC error	Received message fails CRC checksum verification	warning
`743`	Error in the shut down sequence - occurs if the power is cycled off and on too quickly	Power cycled off and back on before shutdown completes	warning
`9`	%SpO2 front end reported syntax error in FSP message	Malformed FSP message received by front end	warning

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.