Key Points for Repairing Medical Ultrasound Power Supplies

1.

When repairing an ultrasound switch power supply, first use a multimeter to scan each power component to see if there is a breakdown or short circuit, such as the power rectifier bridge, switching tube, high-frequency high-power rectifier tube; check if the high-power resistor suppressing surge current is burnt out. Then check if the forward and reverse resistance of each output voltage port is abnormal. If any of the above components are damaged, they need to be replaced before use.

2.

After completing the first step, if it still cannot work normally after turning on the power, then the pulse width modulation component and the power factor module need to be checked. Consult relevant materials and pin functions, and familiarize yourself with the functions of each pin of the PFC and PWM modules and the necessary conditions for the normal operation of the modules.

3.

Then, for power supplies with PFC circuits, it is necessary to measure whether the voltage across the filter capacitor is around 300V. If the voltage is around 300V, it indicates that the PFC module is working normally. Then, check the working status of the PWM component, measure its power input end VC, reference voltage output end VR, and whether the start control Vstart/Vcontrol end voltage is normal. Use a 220VAC/220VAC isolation transformer to supply power to the ultrasound switch power supply, and use an oscilloscope to observe whether the waveform of the PWM module CT to ground is a good linear sawtooth wave or triangle wave, such as the TL494 CT end being a sawtooth wave, and the FA5310 CT end being a triangle wave. Check if the waveform of the output end V0 is an ordered narrow pulse signal.

4.

In the practice of repairing ultrasound switch power supplies, many ultrasound switch power supplies use the UC38×× series 8-pin PWM components. Most ultrasound switch power supplies fail to work because the power supply start-up resistor is damaged, or the chip performance deteriorates. When R is open, there is no power supply, and the PWM component cannot work, so a resistor with the same power resistance as the original one needs to be replaced.

5.

When there is no voltage of about 300V on the filter capacitor, it indicates that the PFC circuit is not working normally. The key detection pins of the PFC module are the power input pin VC, the start pin Vstart/control, the CT and RT pins, and the V0 pin.

In short, no matter how complex the structure of the ultrasound switch power supply is, as long as you grasp its core elements, understand the functions of each part, and are fully familiar with the basic structure of the ultrasound switch power supply and the characteristics of the PWM and PFC modules, and their basic working conditions, following the above steps and methods, thinking more, doing more hands-on work, and carefully repairing the ultrasound switch power supply, you can quickly troubleshoot the ultrasound switch power supply fault and achieve twice the result with half the effort.

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