Digital thermometers · SureTemp Plus family

Welch Allyn SureTemp Plus 690: troubleshooting and error codes

The ServiceForge knowledge base holds 19 documented symptoms for the Welch Allyn SureTemp Plus 690, with 23 ranked causes, 39 diagnostic checks with test points and expected values, and 26 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

Ambient temperature out of range

Display shows capital 'A' followed by blinking up or down arrow and blinking thermometer bulb when ambient temperature exceeds safe range.

Ranked causes

1. Ambient temperature too high (occasional)
2. Ambient temperature too low (occasional)

First check

Verify ambient temperature

Test point: Ambient probe
Expected: 50.0 to 104.0°F, 50.0-104.0°F

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

Calibration: SureTemp Plus 690

Periodic calibration and self-test procedure for units in service or after extended storage

Ranked causes

1. Scheduled preventive maintenance for units in regular service (common)
2. Maintenance required before use after extended storage (common)

First check

Perform Power-On Self Test

Test point: Unit startup
Expected: Self test completes without errors

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

Cleaning with disinfectants caution

Routine and deep cleaning procedures for thermometer and probe

Ranked causes

1. Routine cleaning requirement (common)
2. Deep cleaning with approved disinfectants (common)

First check

Wipe with cloth and warm water with mild detergent

Test point: All exterior surfaces
Expected: Visibly clean, no residue

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

Patient temperature out of range patient safety

Entire body (head, torso, legs) displays blinking with solid up or down arrow and thermometer bulb

Ranked causes

1. Patient temperature above 110.0°F or 43.3°C (occasional)
2. Patient temperature below 80.0°F or 26.7°C (occasional)

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

Battery above operational range

Display shows blinking battery frame, 'b' symbol, and upward arrow when battery voltage exceeds 5.375V.

Ranked causes

1. Battery voltage high (occasional)

First check

Check battery voltage

Test point: Battery
Expected: ≤ 5.375 V

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

Battery below operational range

Display shows blinking battery frame, 'b' symbol, and downward arrow when battery voltage drops below 3.00V.

Ranked causes

1. Battery voltage low (common)

First check

Check battery voltage

Test point: Battery
Expected: ≥ 3.00 V

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

Battery low warning

Single blinking battery segment in battery indicator when voltage is between 3.0V and 3.4V.

Ranked causes

1. Battery voltage declining (common)

First check

Monitor battery voltage trend

Test point: Battery indicator
Expected: Single blinking segment V, > 3.0 and <= 3.4

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

Battery voltage above operational range

Blinking battery frame with 'b' and upward arrow on main display

Ranked causes

1. Battery voltage too high (> 5.375v) (common)

First check

Measure battery voltage

Test point: Battery terminals
Expected: < 5.50 volts
Tools: Voltmeter

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

Battery voltage below operational range

Blinking battery frame with 'b' and downward arrow on main display

Ranked causes

1. Battery voltage too low (< 3.00v) (common)

First check

Measure battery voltage

Test point: Battery terminals
Expected: >= 3.1 volts
Tools: Voltmeter

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

Calibration: SureTemp Plus 690 using Cal-Key

Verify thermometer calibration using the fixed-value Cal-Key (PN 06138-000) method to ensure clinical accuracy

Ranked causes

1. Calibration verification required (common)

First check

Remove any probe currently connected to thermometer

Test point: Device probe port
Expected: Probe disconnected

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

Calibration: SureTemp Plus 690 using Model 9600 Plus Calibration Tester caution

Verify thermometer and probe calibration at three temperature points (36.0ºC, 38.5ºC, 41.0ºC) using Model 9600 Plus Calibration Tester

Ranked causes

1. Three-point calibration verification needed (common)

First check

Store thermometers in same room as Model 9600 Plus for thermal accommodation

Test point: Room temperature environment
Expected: Approximately 30 minutes storage time

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

Instrument error detected

Instrument with X through it displayed with error code in temperature field; temperature measuring prohibited

Ranked causes

1. Internal instrument circuitry failure (rare)

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

Low battery shutdown

Device automatically shuts off when battery voltage degrades below threshold to prevent erroneous temperature readings

Ranked causes

1. Battery voltage below 3 volts (common)

First check

Measure battery voltage

Test point: Battery terminals
Expected: 3.60V nominal (fresh), minimum 3.0V operating, minimum threshold

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

Power-on self test failure

Device performs POST when battery power is applied to check internal hardware and stored calibration values

Ranked causes

1. Factory calibration not intact (unknown)

First check

Verify battery voltage and POST completion

Test point: Power supply output
Expected: Peak 4.8V, average 3.60V

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

Probe error detected

Probe with X through it displayed with error code in temperature field; temperature measuring prohibited

Ranked causes

1. Broken or malfunctioning probe (common)

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

Probe type detection

Thermometer reads probe EEPROM to determine probe type (Oral/Axillary or Rectal) and load appropriate calibration values

Ranked causes

1. Probe EEPROM not readable or corrupted (rare)

First check

Verify probe detection on insertion

Test point: Optical probe detection switch
Expected: High-to-Low transition when probe pulled from well

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

Six-month visual inspection and cleaning

Regular inspection for physical damage and cleaning of units in active service

Ranked causes

1. Regular preventive maintenance for active-service units (common)

First check

Visually inspect for physical damage

Test point: Entire thermometer exterior and probe
Expected: No cracks, dents, or visible defects

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

Thermistor measurement accuracy

Thermometer measures thermistor resistance to calculate patient temperature using nonlinear equation

Ranked causes

1. Thermistor degradation or out-of-spec resistance (occasional)

First check

Measure thermistor resistance at room temperature

Test point: Thermistor element
Expected: Approximately 20K ohms

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

Unit storage maintenance

Procedures for thermometers stored for extended periods to ensure functionality before reuse

Ranked causes

1. Stored unit requires reactivation maintenance (common)

First check

Remove and reinstall batteries

Test point: Battery compartment
Expected: Batteries removed then reinstalled

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

Error codes

Code	Meaning	Trigger	Severity
`23`	Host Interface Error	Communication failure with host interface	error
`26`	Invalid SureTemp mode	Device mode setting is invalid or corrupted	warning
`29`	Battery Voltage Is Not Set	Battery voltage parameter not configured in device memory	warning
`30`	Prediction mode Is Not Set	Prediction mode parameter not configured in device memory	warning
`71`	Device EEPROM acquire failure	Device cannot acquire lock or access to EEPROM	error
`72`	Device EEPROM release failure	Device cannot release EEPROM after access	error
`73`	DEVICES EEPROM invalid pointer failure	EEPROM memory pointer is invalid or corrupted	error
`E0.1`	Excessive Heater Energy	Heater produces excessive energy during measurement cycle	error
`E0.2`	A/D Measurement out of range error	Analog-to-digital converter measures value outside valid range	error
`E0.4`	Probe Over Temperature	Probe tip temperature exceeds 110°F/43.3°C	warning
`E0.5`	No Probe Temperature Rise	Probe heater has no effect on temperature measurement	error
`E0.6`	Probe EEPROM read failure	Bad EEPROM handshake between probe and device	error
`E0.7`	Probe EEPROM is un-initialized	Probe memory not properly initialized	error
`E0.8`	EEPROM CRC Failure	EEPROM data integrity check fails	error
`E0.9`	Bad probe calibration	Probe calibration data is invalid or corrupted	error
`E4.0`	PTB measurement out of range	Patient Temperature Buffer measurement exceeds valid range	error
`E4.1`	RCAL measurement out of range	Reference calibration measurement exceeds valid range	error
`E4.2`	Reference power supply malfunction	Internal reference power supply fails operational test	error
`E4.3`	Device EEPROM save failure	Device unable to write to internal EEPROM memory	error
`E4.4`	Device EEPROM starting handshake failure	Initial communication with EEPROM fails at startup	error
`E4.5`	Device EEPROM response failure	EEPROM does not respond to read/write commands	error
`E4.6`	Transmit failure to the Device EEPROM	Device unable to transmit data to internal EEPROM	error
`E4.7`	Can't initialize the device EEPROM	Device EEPROM initialization sequence fails	error
`E4.8`	Device was not calibrated	Device does not have valid calibration data loaded	error
`E5.0`	Heater is not working properly	Internal heater circuit malfunction detected	error
`E5.2`	Heater fail-safe failure	Heater fail-safe protective circuit malfunction	critical

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.