Pulse oximeters · OXIMAX family

Nellcor N-65: troubleshooting and error codes

The ServiceForge knowledge base holds 20 documented symptoms for the Nellcor N-65, with 57 ranked causes, 43 diagnostic checks with test points and expected values, and 82 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Monitor does not turn on

Power button pressed but monitor does not power up or display anything

Ranked causes

1. Power button not fully depressed (common)
2. Batteries missing (occasional)
3. Batteries installed incorrectly (occasional)
4. Battery voltage too low (occasional)
5. Flex circuit damaged or disconnected (rare)
6. Front panel keypad defective (rare)
7. SpO2 PCB defective (rare)
8. User Interface PCB defective (rare)

First check

Verify power button is fully pressed

Test point: Power button
Expected: Power button depresses completely with audible click

4 more checks with pass and fail actions, 8 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Unit does not power on

No power indication when POWER key pressed

Ranked causes

1. Power button not fully depressed (common)
2. Batteries missing (common)
3. Batteries installed incorrectly (common)
4. Battery voltage too low (occasional)
5. Flex circuit damaged or disconnected (rare)
6. Front panel keypad defective (rare)
7. SpO2 PCB defective (rare)
8. User Interface PCB defective (rare)

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

Calibration: Pulse Oximetry Functional Tests patient safety

Verification of monitor performance using SRC-MAX functional tester to validate BPM, SpO2, modulation, and light level readings against expected values.

Ranked causes

1. Monitor requires performance verification after service (common)
2. BPM reading verification required (common)
3. SpO2 reading verification required (common)
4. Modulation level verification required (common)
5. Light level verification required (common)

First check

Power on monitor and connect SRC-MAX tester with DEC-4 extension cable to sensor port

Test point: Sensor Port
Expected: SRC-MAX panel lights and monitor tracks simulator within seconds

9 more checks with pass and fail actions, 5 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Display backlight not illuminating

Backlight does not come on when BACKLIGHT key pressed

Ranked causes

1. Flex circuit damaged or disconnected (common)
2. BACKLIGHT key defective (occasional)
3. SpO2 PCB defective (rare)
4. User Interface PCB defective (rare)
5. BACKLIGHT LEDs failed (rare)

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

Front panel keys not working

One or more keypad keys do not respond to pressing

Ranked causes

1. Flex circuit damaged or disconnected (common)
2. Front panel keypad defective (occasional)
3. SpO2 PCB defective (rare)
4. User Interface PCB defective (rare)

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

No pulse rate or SpO2 value displayed patient safety

Pulse rate and oxygen saturation values do not show on display

Ranked causes

1. SpO2 sensor not connected properly (common)
2. SpO2 sensor failed (occasional)
3. User Interface PCB defective (rare)
4. SpO2 PCB defective (rare)

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

One or more keypad keys not working

One or more front panel keys do not respond when pressed

Ranked causes

1. Flex circuit damaged or disconnected (common)
2. Front panel keypad defective (occasional)
3. SpO2 PCB defective (rare)
4. User Interface PCB defective (rare)

First check

Inspect flex cable between front panel and PCB

Test point: Flex cable and J4 connector
Expected: Flex cable intact, no visible damage, J4 fully seated

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

Pulse rate and SpO2 not displayed patient safety

Monitor powered on but no pulse rate or oxygen saturation values displayed

Ranked causes

1. SpO2 sensor not connected (common)
2. SpO2 sensor failure (occasional)
3. User Interface PCB defective (rare)
4. SpO2 PCB defective (rare)

First check

Verify SpO2 sensor is connected to monitor

Test point: SpO2 sensor connector at monitor
Expected: Connector fully seated and secure

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

Calibration: Overall Performance Check patient safety

Qualitative system performance verification using a live subject with MAX-A adult SpO2 sensor to confirm normal operation

Ranked causes

1. System requires performance verification before clinical use (common)
2. Sensor attachment to live subject required (common)

First check

Sensor connection to oximeter

Test point: Sensor input port
Expected: Sensor properly connected

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

Display segments not working

One or more LCD display segments do not illuminate

Ranked causes

1. User Interface PCB component failed (occasional)
2. User Interface PCB defective (occasional)

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

One or more display segments not working

Display segments on front panel do not illuminate or display information

Ranked causes

1. User Interface PCB component failure (common)
2. User Interface PCB defective (occasional)

First check

Visually inspect User Interface PCB

Test point: User Interface PCB surface
Expected: No cracking, burning, discoloration, or visible component damage

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

Calibration: Power-On-Self-Test (POST) verification patient safety

Verify monitor is working properly and safe for patient use before deployment. POST takes approximately 10 seconds to complete and tests monitor circuitry and functions automatically on power-on.

Ranked causes

1. Monitor fails Power-On-Self-Test (unknown)

First check

Verify all indicators and display elements light during power-on

Test point: Display and indicator panel
Expected: All indicators and display elements illuminate

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

Display backlight does not illuminate

Backlight button pressed but display does not light up

Ranked causes

1. Flex circuit damaged or disconnected (common)

First check

Press backlight button and observe display

Test point: Display area
Expected: Backlight illuminates when button pressed

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

POST error code displayed caution

Monitor displays error code (Er) with error number instead of passing POST

Ranked causes

1. Internal monitor circuitry fault detected (unknown)

First check

Note error code number displayed

Test point: Display error code field
Expected: Er followed by specific error number

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

Power-On-Self-Test (POST) does not produce pass tone patient safety

Unit powers on but does not emit the expected POST pass tone, indicating self-test failure

Ranked causes

1. Speaker obstructed or blocked (common)

First check

Verify speaker is clear of obstructions

Test point: Speaker assembly
Expected: Speaker holes fully unobstructed, no debris or blockage visible

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

Power-On-Self-Test verification

Monitor must complete POST sequence with all display segments and icons shown, software version displayed, and POST pass tone sounding within ~10 seconds of power-on

Ranked causes

1. POST fails to complete or pass tone does not sound (rare)

First check

Press Power button and observe display sequence

Test point: Display and backlight
Expected: All display graphics shown for 3 seconds with backlight on

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

Unit shuts off when BACKLIGHT key pressed

Oximeter powers down when BACKLIGHT key is activated

Ranked causes

1. Battery voltage too low (common)

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

Verification: Monitor display stabilization time

Monitor requires stabilization time (displays dashes) when SpO2 level changes, before final reading displays.

Ranked causes

1. Normal SpO2 measurement stabilization delay (common)

First check

Observe monitor response time to SpO2 90% setting

Test point: Monitor display
Expected: Three dashes briefly, then stable 90 %SpO2 display

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

Verification: SpO2 alarm condition during functional tests

Monitor enters SpO2 alarm state during test setup and most functional test steps, which is expected behavior during low saturation simulation.

Ranked causes

1. SpO2 level set below alarm threshold by SRC-MAX during tests (common)

First check

Confirm SpO2 alarm active during Test Setup and low saturation tests

Test point: Monitor alarm indicator
Expected: Alarm active during SpO2 75% setting

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

Verify monitor operation after repair or maintenance patient safety

Performance verification tests to ensure OXIMAX N-65 is safe and ready for patient monitoring before returning to user

Ranked causes

1. Unknown - verification test procedure required (unknown)

First check

Verify all indicators and display elements light during power-on

Test point: Monitor display and indicator lights
Expected: All indicators and display elements light when powered on

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

Error codes

Code	Meaning	Severity
`1`	SpO2 front end RAM error	error
`10`	SpO2 front end reports over current failure	error
`11`	SpO2 front end reports incorrect system voltage	error
`12`	SpO2 front end reports other hardware problem	error
`14`	SpO2 front end reports communication channel overflow	error
`16`	SpO2 front end reports watchdog time out	error
`17`	SpO2 front end reports that sensor appears defective	error
`18`	SpO2 front end reports internal register appears modified from expected value	error
`19`	SpO2 front end reports signal out-of-range	error
`2`	SpO2 front end ROM/code integrity error	error
`256`	SpO2 back end reports beginning of packet missing	error
`257`	SpO2 back end reports packet start ID (SID) missing	error
`258`	SpO2 back end reports packet length error	error
`259`	SpO2 back end reports message length error	error
`260`	SpO2 back end reports packet contains unsupported key	error
`261`	SpO2 back end reports packet CRC error	error
`262`	SpO2 back end reports end of packet missing	error
`263`	SpO2 back end reports packet contains unidentified key	error
`264`	SpO2 back end reports corrupted variable	error
`265`	SpO2 back end reports memory overflow	error
`266`	SpO2 back end reports bad pointer	error
`267`	SpO2 back end reports parameter value out-of-range	error
`268`	SpO2 back end reports reset detected	error
`269`	SpO2 back end reports unexpected value	error
`270`	SpO2 back end reports time-out	error
`271`	SpO2 back end reports not ready/not initialized	error
`272`	SpO2 back end reports double fault	critical
`273`	SpO2 back end reports date out-of-range error	warning
`274`	SpO2 back end reports incompatible software version	error
`275`	SpO2 back end reports incorrect registration number	error
`276`	SpO2 back end reports sensor read failure	error
`277`	SpO2 back end reports sensor signature verification fails	error
`280`	SpO2 back end reports does not support feature required by sensor	error
`281`	SpO2 back end reports overflow/underflow	error
`282`	SpO2 back end reports sensor activation failure	error
`3`	SpO2 front end reported a bad CRC	error
`4`	SpO2 front end reported FSP message not allowed	error
`48`	SpO2 front end reports spurious interrupt	error
`49`	SpO2 front end reports internal buffer overflow	error
`5`	SpO2 front end reported illegal value sent in FSP message	error
`50`	SpO2 front end reports intermittent error	error
`51`	SpO2 front end reports digital communication error	error
`512`	Communication failure with real time clock	critical
`513`	Real time clock oscillator control problem	critical
`514`	Real time clock failed timing test	error
`515`	LCD failed feedback test	error
`516`	LCD failed feedback test	error
`518`	Various system faults	critical
`519`	Unrecoverable software error	critical
`520`	Unrecoverable error verify real time clock	critical
`521`	Battery power is critically low	warning
`522`	System power levels unacceptable for continued operation	warning
`523`	NVRAM failed consistency check	error
`524`	NVRAM failed read-after-write verification	error
`525`	Time base discrepancy writing error entry	error
`526`	Fatal error for SpO2 communication	critical
`527`	Communication failure with SpO2 board	critical
`528`	Fatal error creating parser	critical
`529`	Fatal error creating parser	critical
`53`	SpO2 front end data not received	error
`530`	Unrecoverable error with SpO2 communication	critical
`531`	Unrecoverable error with SpO2 communication	critical
`532`	Unrecoverable error with SpO2 communication	critical
`533`	Unrecoverable error with SpO2 communication	critical
`534`	Unrecoverable error with SpO2 communication	critical
`535`	Unrecoverable error with SpO2 communication	critical
`536`	Flash memory failed CRC check	error
`537`	Fatal system error	critical
`538`	Real time clock value bad	warning
`539`	Erroneous key press detected at start	warning
`540`	Fatal system error reading memory	critical
`541`	Fatal software error	critical
`542`	RAM corruption detected during background check	error
`543`	Invalid time. Cannot snapshot.	info
`544`	Invalid register value	error
`545`	SpO2 board in unexpected state	error
`546`	IrDA failure	error
`6`	SpO2 front end reports calibration (offset) failure	error
`9`	SpO2 front end reported syntax error in FSP message	error
`997`	RAM error	error
`998`	Spurious Interrupt	error
`999`	Watchdog protection activated	error

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.