Patient monitors

SunTech Medical Tango: troubleshooting and error codes

The ServiceForge knowledge base holds 19 documented symptoms for the SunTech Medical Tango, with 36 ranked causes, 37 diagnostic checks with test points and expected values, and 0 error codes. Each symptom below shows its causes and the first check; the rest is one connection away. Connect ServiceForge to your AI

Symptoms

ECG signal detection failure or K-sound detection error patient safety

Unit fails to detect ECG signal or K-sounds correctly, displays ---/--- for BP, resets signal gains

Ranked causes

1. No ECG signal detected for 60 seconds (common)
2. Incorrect Bin Skip setting (occasional)
3. Incorrect ECG Delay setting (occasional)

First check

Verify Bin Skip setting in Maintenance Menu

Test point: Maintenance Menu Configuration
Expected: Value 3 for Digital ECG trigger or 0 for Analog ECG trigger

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

ECG signal not received or recognized

External ECG trigger not detected, or internal ECG board not operational when configured for standalone mode

Ranked causes

1. ECG cable not connected to BNC input (common)
2. External ECG source not providing trigger signal (occasional)
3. Optional internal ECG board not installed or failed (occasional)

First check

Verify ECG trigger input method selected in software

Test point: Maintenance menu configuration
Expected: ECG input source matches connected hardware

1 more check with pass and fail actions are in ServiceForge. Connect ServiceForge to your AI

K-Sound signal weak or absent

K-Sound microphone input not detected, signal level too low for analysis, no Korotkoff sounds recognized

Ranked causes

1. Microphone disconnected or defective (common)
2. K-Sound amplifier stage failure (occasional)
3. K-Sound gain control (U27) failure (rare)

First check

Verify K-Sound patient cable connected to J100

Test point: J100 connector
Expected: Cable seated and secure, no visible damage

Overpressure or timeout shutdown occurs patient safety

Pump and valve circuit shuts down unexpectedly, possibly indicating pressure limit or timeout activation

Ranked causes

1. Cuff or tubing blocked causing overpressure (common)
2. Overpressure sensor (X2) false trigger (occasional)
3. Timeout circuit activation (160-180 second limit exceeded) (occasional)

First check

Verify cuff and tubing are clear of blockage

Test point: Patient cable, cuff, and connections
Expected: No restrictions in pneumatic path

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

Serial communication failure

No data transmission to/from host system via RS232 port, command not received or data not sent

Ranked causes

1. RS232 port not connected or incorrectly wired (common)
2. Slave CPU communication failure (occasional)
3. Master CPU (U41) failure (rare)

First check

Verify RS232 cable connected to J8

Test point: J8 on main board
Expected: 9-pin connector seated and secure

Abnormal power supply voltages caution

One or more voltage rails measure outside tolerance when 9VDC applied to J1

Ranked causes

1. Failed voltage regulator (common)
2. Power supply input not connected correctly (occasional)

First check

Measure voltage at TP8 (VIN)

Test point: TP8
Expected: 8.1VDC, ±5% (7.70-8.50V)

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

Bleed valve not responding or stuck patient safety

Bleed valve V1 or V2 will not open/close, remains stuck in one position, or responds erratically to commands

Ranked causes

1. Bleed valve solenoid stuck or deactivated (occasional)
2. Bleed valve mechanical blockage (occasional)

First check

Command bleed valve to open (255) and closed (0) from maintenance menu

Test point: Bleed valve control in menu
Expected: Valve responds smoothly to commands
Tools: Maintenance menu access

High power supply current draw caution

Current demand exceeds normal limits after power-up or during operation

Ranked causes

1. Short circuit in power rail (rare)
2. Component failure causing leakage current (occasional)

First check

Measure supply current 5 seconds after power-up

Test point: Power supply input
Expected: 450-625mA, 450-625mA
Tools: Multimeter set to current range

Oscillometric mode not available or not functioning patient safety

Unit configured for oscillometric mode but readings not obtained, or mode disabled in later software versions

Ranked causes

1. Software version 1.33/3.28I or later (oscillometric feature removed) (common)
2. Oscillometric pressure circuit (X1 transducer) failure (occasional)

First check

Check unit software version via LCD menu or documentation

Test point: Firmware version display
Expected: Software version 1.32/3.27I or earlier for oscillometric capability

Pump does not operate or operates erratically patient safety

Pump fails to run when commanded, runs continuously, or does not build pressure as expected

Ranked causes

1. Pump mechanical failure or blockage (occasional)
2. Power supply to pump circuit failed (common)

First check

Measure pump motor current consumption

Test point: Power supply input with pump ON
Expected: 375-475mA pump delta current, 375-475mA
Tools: Multimeter on current range

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

Real-time clock or non-volatile memory failure

System time incorrect, settings not retained after power-off, calendar displays wrong date

Ranked causes

1. B1 backup battery depleted (common)
2. Real-time clock IC failure (rare)

First check

Measure voltage at TP19 (VBAT) with unit powered off

Test point: TP19
Expected: 3.0VDC, 2.85-3.30V

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

Valve does not open or close patient safety

Valve V1 or V2 fails to respond to control commands or remains in one state

Ranked causes

1. Valve solenoid failure (occasional)
2. Valve control circuit failure (rare)

First check

Verify valve opens and closes on command from maintenance menu

Test point: Valve V1 or V2
Expected: Valve responds to open/close commands
Tools: Maintenance menu access

Calibration required message displayed on boot-up caution

Unit displays calibration required message upon startup and emits warning beep

Ranked causes

1. Annual calibration reminder timeout (1 year of field use) (common)

First check

Verify firmware version supports calibration reminder

Test point: Boot-up display
Expected: Version 1.33/3.28I or greater

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

Calibration: Pressure verification

Monitor displays 'Please VERIFY CALIBRATION' or 'Equipment Maintenance and Calibration Required' message

Ranked causes

1. Pressure calibration verification required (unknown)

First check

Access VERIFY CALIBRATION menu

Test point: Monitor display screen
Expected: VERIFY CALIBRATION screen displayed, bleed valves closed

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

Calibration: Reset calibration reminder

Reset the calibration verification reminder after successful pressure calibration

Ranked causes

1. Calibration reminder reset (unknown)

First check

Enter diagnostic menu

Test point: SELECT button and arrow keys
Expected: DIAGNOSTIC MENU displayed

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

Calibration: Verify 75Hz signal attenuation response

Functional test of signal attenuator and input filter frequency response at 75Hz fundamental with noise rejection

Ranked causes

1. Attenuator or filter circuit malfunction (unknown)

First check

Measure signal amplitude at U3-1 with first attenuator input driven

Test point: U3-1
Expected: Clean sine wave 1.8 to 2.2Vp-p, +/-0.2 Vp-p
Tools: Oscilloscope, signal generator (2.50Vpp 75Hz)

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

Calibration: Verify ECG signal conditioning and amplitude scaling patient safety

Test ECG input signal path from patient cable through isolation and conditioning stages with ECG simulator at multiple amplitude settings

Ranked causes

1. ECG signal path malfunction or isolation transformer fault (unknown)

First check

Connect ECG simulator to patient cable and UUT

Test point: J1 pins 1 (V2), 2 (RL), 3 (V6)
Expected: ECG simulator properly connected per cable assembly pinout

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

Display returns to K-Sound after 60 seconds of ECG display

After user selects ECG display from menu, system automatically reverts to K-Sound waveform display after 60 seconds of inactivity

Ranked causes

1. Firmware timer function for display auto-switch (common)

Re-inflate on first measurement if systolic exceeds initial inflate pressure patient safety

Monitor automatically re-inflates cuff on first patient measurement when systolic pressure exceeds the initial inflation target pressure

Ranked causes

1. Systolic pressure higher than initial cuff inflation pressure (occasional)

1 corrective action and part numbers 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.