Pulse oximeters

Nellcor NPB-295: troubleshooting and error codes

The ServiceForge knowledge base holds 15 documented symptoms for the Nellcor NPB-295, with 38 ranked causes, 37 diagnostic checks with test points and expected values, and 14 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Battery Low indicator lights steadily while connected to AC with fully charged battery

Battery Low indicator remains on continuously despite AC power connection and full battery charge

Ranked causes

1. AC outlet not operational or AC indicator not on (common)
2. Fuses blown or defective (common)
3. Power supply output voltage or current out of specification (occasional)
4. Ribbon connection from bottom enclosure to UIF PCB loose or defective (occasional)
5. UIF PCB defective (occasional)

First check

Verify AC power connection

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

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

No printout from serial data port

NPB-295 fails to transmit data through serial port; connected printer or external device receives no output

Ranked causes

1. Monitor running on battery power instead of AC (common)
2. Monitor and printer baud rate mismatch (occasional)
3. Monitor data port protocol setting incorrect (occasional)
4. UIF PCB defective (occasional)

First check

Verify monitor is connected to AC power source

Test point: AC indicator and power status
Expected: Monitor powered from AC outlet with AC indicator illuminated

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

RS-232 nurse call function not working patient safety

Nurse call output via serial port fails to operate; no signal or alarm transmission to nurse call system

Ranked causes

1. Monitor running on battery power instead of AC (common)
2. Nurse call connections missing or incorrect (occasional)
3. Nurse call output voltage out of specification (occasional)
4. UIF PCB defective (occasional)

First check

Verify monitor is connected to AC power source

Test point: AC indicator and power status
Expected: Monitor powered from AC outlet with AC indicator illuminated

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

Display pixels do not light

LCD display pixels fail to illuminate; display appears dark or blank

Ranked causes

1. UIF PCB to Display PCB connection loose or defective (common)
2. Display PCB defective (occasional)
3. UIF PCB defective (occasional)

First check

Verify UIF PCB to Display PCB connection

Test point: Ribbon connector or cable between PCBs
Expected: Firmly seated connection with no visible damage

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

Display values missing or erratic

LCD display shows missing or erratic digital values during normal operation

Ranked causes

1. Sensor connector assembly defective or loose (common)
2. Sensor extension cable defective (occasional)
3. UIF PCB defective (occasional)

First check

Verify sensor connector assembly connection and integrity

Test point: Sensor connector assembly
Expected: Connector firmly seated and undamaged

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

SpO2 or Pulse values change rapidly; Pulse AMPLITUDE indicator erratic

Display values for SpO2 and pulse rate fluctuate rapidly; LED pulse amplitude indicator behaves inconsistently

Ranked causes

1. Pulse oximetry sensor damp or reused excessively (common)
2. Electrosurgical unit (ESU) interference with NPB-295 (occasional)
3. UIF PCB defective (occasional)

First check

Inspect pulse oximetry sensor for moisture and reuse count

Test point: Sensor physical condition and usage history
Expected: Sensor dry and within reuse limits

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

Alarm does not sound patient safety

Audible alarm fails to activate when alarm condition occurs

Ranked causes

1. Speaker defective or disconnected (common)
2. UIF PCB defective (occasional)

First check

Trigger an alarm condition and listen for audible tone

Test point: Speaker output
Expected: Clear audible alarm tone when alarm condition occurs

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

Alarm sounds for no apparent reason

Audible alarm activates spontaneously without triggering condition or error code

Ranked causes

1. Moisture or spilled liquid present in monitor (common)
2. UIF PCB defective (occasional)

First check

Inspect for moisture or liquid contamination

Test point: Interior of monitor housing, PCBs, connectors
Expected: No visible moisture, liquids, or condensation

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

Battery does not charge

Battery fails to accept or hold a charge when NPB-295 is connected to AC power

Ranked causes

1. Battery exceeds 2 years age and has reached end of life (common)
2. Power supply output voltage or current out of specification (occasional)

First check

Verify battery age

Test point: Battery manufacturing date or installation date
Expected: Battery less than 2 years old

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

NPB-295 does not operate when disconnected from AC power

Unit fails to function on battery power alone

Ranked causes

1. Battery is discharged (common)
2. Battery defective or failed (occasional)

First check

Verify battery charge level

Test point: Battery indicator or display
Expected: Adequate charge indicated

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

NPB-295 responds to some but not all buttons

Monitor responds inconsistently to button presses; some buttons functional, others non-responsive

Ranked causes

1. Top Housing assembly defective or worn (common)
2. UIF PCB defective (occasional)

First check

Test all buttons for response

Test point: All front panel buttons
Expected: All buttons should respond to presses

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

NPB-295 turns on but does not respond to any buttons

Monitor powers up but is unresponsive to all button inputs

Ranked causes

1. Top Housing assembly defective (common)
2. UIF PCB defective (occasional)

First check

Test all buttons for any response

Test point: All front panel buttons
Expected: At least one button should respond

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

Pulse AMPLITUDE indicator shows pulse but digital displays show zeroes

LED pulse amplitude indicator illuminates indicating pulse detection, but SpO2 and pulse rate displays show zero values

Ranked causes

1. Pulse oximetry sensor damaged or defective (common)
2. UIF PCB defective (occasional)

First check

Inspect pulse oximetry sensor for damage

Test point: Sensor physical condition
Expected: Sensor undamaged and properly positioned on patient

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

Battery Low indicator on during DC operation with alarm sounding patient safety

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

Ranked causes

1. 15 minutes or less of usable battery charge remaining (common)

First check

Monitor time remaining on battery

Test point: Battery Low indicator and alarm status
Expected: Approximately 15 minutes of usable charge remaining

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

Battery voltage critical, unit displays error code patient safety

When unit is on and battery voltage drops to critical level (5.67 ± 0.1 V), an error code is displayed and unit will not monitor patient. Unit runs for 15 minutes then powers down.

Ranked causes

1. Battery voltage below 5.67 ± 0.1 volts DC (common)

First check

Measure battery voltage at UIF PCB

Test point: Battery terminals
Expected: 5.67 ± 0.1 volts DC or higher V, ±0.1 V

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

Error codes

Code	Meaning	Severity
`1`	POST failure	critical
`11`	Flash ROM corruption	error
`12`	Excessive resets	error
`4`	Battery dead	warning
`5`	Too many microprocessor resets within a period of time	warning
`52`	Loss of settings	info
`6`	Boot CRC error	error
`7`	Error on UIF PCB	error
`76`	Error accessing EEPROM	error
`8`	Boot CRC Error	error
`80`	Institutional default values lost and reset to factory default values	info
`81`	Settings lost (custom settings different from power-on defaults)	info
`82`	Time clock lost	warning
`84`	Internal communications error	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.