Pulse oximeters

Nellcor NPB-290: troubleshooting and error codes

The ServiceForge knowledge base holds 9 documented symptoms for the Nellcor NPB-290, with 20 ranked causes, 17 diagnostic checks with test points and expected values, and 11 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Unit does not power up on AC or DC caution

Monitor fails to turn on when connected to AC power or battery power; no lights or display activity.

Ranked causes

1. AC outlet not operational or AC indicator not lit (common)
2. Fuses blown in Power Entry Module (common)
3. Power supply output to battery incorrect (occasional)
4. Battery discharged (common)
5. Cable connection from bottom enclosure to User Interface PCB loose or damaged (occasional)

First check

Verify AC outlet is operational and monitor is connected

Test point: AC outlet and AC indicator
Expected: AC indicator on

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

Battery not charging or dead

Pulse oximeter battery depleted or not accepting charge, preventing operation on battery power

Ranked causes

1. Voltage selector switch set incorrectly (common)
2. Battery not fully charged (common)
3. Battery leads reversed (occasional)
4. Battery module failed (occasional)

First check

Voltage selector switch set correctly per N-290 operator manual

3 more checks with pass and fail actions are in ServiceForge. Connect ServiceForge to your AI

Battery low indicator lights while on AC power with fully charged battery caution

BATTERY LOW indicator continuously illuminated even when monitor is plugged into operational AC outlet and battery is fully charged.

Ranked causes

1. Power supply voltage output incorrect (common)
2. Cable connection from bottom enclosure to User Interface PCB loose (occasional)
3. User Interface PCB defective (occasional)

First check

Verify AC power connection and indicator status

Test point: AC outlet and AC indicator on monitor
Expected: AC indicator illuminated

2 more checks with pass and fail actions, 3 corrective actions, and part numbers are in ServiceForge. Connect ServiceForge to your AI

Monitor does not operate when disconnected from AC power caution

Unit fails to run on battery power alone; no display or operation when unplugged from AC outlet.

Ranked causes

1. Battery discharged (common)
2. Battery defective or aged (more than 2 years old) (occasional)

First check

Verify battery charge level and recharge if depleted

Test point: Monitor battery via AC recharge
Expected: Battery fully charged after 14 hours on AC power; monitor operates on battery

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

Monitor powers down without apparent cause during use caution

Unit unexpectedly shuts off while operating on battery or AC power; loss of display and function.

Ranked causes

1. Battery low or discharged during DC operation (common)
2. Battery aged (more than 2 years) or defective (occasional)

First check

Check BATTERY LOW indicator and alarm status

Test point: Monitor display and audio alarm
Expected: BATTERY LOW indicator lit and alarm sounding during DC operation

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

Analog output plethysmographic waveform calibration

Calibrate plethysmographic waveform output where 1.0 volt DC = 255 pulse amplitude units (pau); verify output decreases proportionally as waveform amplitude decreases

Ranked causes

1. Plethysmographic waveform output scaling verification (common)

First check

Measure plethysmographic waveform output at various amplitudes

Test point: Plethysmographic analog output
Expected: 1.0V at 255 pau, proportionally less at lower amplitudes
Tools: Digital voltmeter or oscilloscope

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

Analog output pulse rate signal calibration

Calibrate pulse rate output where 1.0 volt DC = 250 bpm; verify output decreases proportionally as pulse rate decreases

Ranked causes

1. Pulse rate output scaling verification (common)

First check

Measure pulse rate output at various bpm levels

Test point: Pulse rate analog output
Expected: 1.0V at 250 bpm, proportionally less at lower pulse rates
Tools: Digital voltmeter

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

Analog output saturation signal calibration

Calibrate saturation output where 1.0 volt DC = 100%; verify output decreases proportionally as saturation values decrease

Ranked causes

1. Saturation output scaling verification (common)

First check

Measure saturation output at various SpO2 levels

Test point: Saturation analog output
Expected: 1.0V at 100%, proportionally less at lower saturations
Tools: Digital voltmeter

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

Power-on self-test fails caution

Monitor powers on but fails power-on self-test (POST) and may display error or not complete initialization.

Ranked causes

1. User Interface PCB defective (rare)

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

Error codes

Code	Meaning	Trigger	Severity
`1`	POST failure	Power-on self-test failure on startup	critical
`11`	Flash ROM corruption	Flash memory data integrity loss	critical
`4`	Battery dead	Battery depleted or unable to charge	critical
`5`	Too many microprocessor resets within period of time	Processor unstable or repeatedly crashing	critical
`52`	Institutional default values lost and reset to factory default	Custom configuration data lost	warning
`6`	Boot CRC error	Boot firmware checksum verification failed	critical
`7`	Error on User Interface PCB	User Interface PCB hardware failure	critical
`76`	Error accessing EEPROM	EEPROM read/write failure	critical
`80`	Institutional default values lost and reset to factory default	Custom configuration data lost	warning
`82`	Time clock lost	Real-time clock data or battery lost	warning
`84`	Internal communications error	PCB-to-PCB communication failure	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.