Troubleshooting the Mindray DP-50 Portable Ultrasound Display

During daily use, medical ultrasound equipment often encounters various malfunctions, including hardware and software failures. The causes of these malfunctions can be multifaceted, including:Improper usage, aging components, dust accumulation, circuit load, short circuits, etc.Since ultrasound equipment is not a therapeutic device, and malfunctions do not usually affect the quality of ultrasound image display, general ultrasound malfunctions do not directly harm the patient's body.

However, due to the widespread use of ultrasound examinations, most hospitals' ultrasound equipment operates at full capacity. Once ultrasound equipment stops functioning due to malfunctions, it will affect the timeliness of disease screening for patients.

This article introduces the Mindray DP-50 ultrasound device. This is a monochrome portable ultrasound device, belonging to the brand's high-end monochrome ultrasound series. It has basic disease screening functions and is lightweight and portable (weighing only about 5 kg).

This article focuses on a monitor malfunction of this ultrasound model. By describing the malfunction phenomenon and the resolution process, it provides a reference for similar equipment malfunctions, allowing maintenance engineers to quickly find the cause of the malfunction and repair it when encountering related problems.

1、Basic Equipment Information 

Model DP-50 Fully Automatic Portable Ultrasound Diagnostic System (Mindray). This device is a higher-end version of the DP series ultrasound, featuring iTouch one-button image optimization, iBeam composite imaging, iClear speckle noise suppression, and broadband frequency-shifted harmonic technologies.

2、Basic Principles of Medical Ultrasound

The principle of medical ultrasound is relatively simple. It transmits ultrasonic waves to human tissues. Due to the acoustic specificity of human tissues, reflection, refraction, scattering, diffraction, attenuation, and Doppler frequency shift due to the relative motion of the sound source and receiver occur at different tissue interfaces. These reflected and scattered signals are received by the ultrasound instrument, processed, and displayed on the monitor, allowing physicians to observe and judge tissue morphology through ultrasound images.

3、Equipment Malfunction

Malfunction Phenomenon:

After normal startup for a period of time, a horizontal band of bright lines sometimes appears on the monitor, affecting the observation of the ultrasound image.

Malfunction Analysis:

 Based on the malfunction phenomenon, it is initially judged that the cause may be a malfunction in the display's field scanning circuit. First, consider poor contact in the circuit. After carefully inspecting the circuit board, malfunctions caused by poor contact were ruled out. No abnormalities were found in the field circuit components using resistance measurement.

Since the malfunction does not occur all the time and returns to normal after appearing, careful observation revealed a 0.5 cm wide scan line with lower brightness below the horizontal bright line. It was initially judged that one of the components in the field scanning circuit was exhibiting unstable performance.

The field scanning circuit consists of a field oscillation stage, an excitation stage, a field output stage, and a field deflection coil. The field oscillation circuit generates a 50 Hz sawtooth wave oscillating voltage through a self-excited intermittent oscillation. Under the control of the field synchronization signal, it outputs a synchronous sawtooth wave oscillating voltage to the excitation stage.

The excitation stage amplifies the sawtooth wave oscillating voltage signal to sufficiently drive the field output stage. The field output circuit is actually a low-power amplifier, and its load is the field deflection coil. Because the field frequency is low, the reactance of the deflection coil is far less than its DC resistance. During the scanning forward stroke, it is a power amplifier, while during the reverse stroke, due to the short time, the reactance effect increases, and a high induced voltage higher than the supply voltage will be generated at both ends of the deflection coil. This field output uses an OTL circuit (Figure 1),

The alternating conduction and cutoff of the two complementary symmetrical field output tubes correspond to the first and second half of the field scanning forward stroke and the first and second half of the reverse stroke. During the latter half of the forward and the latter half of the reverse scan, BG2 conducts. In the other three halves, BG1 works; in the first half of the forward stroke and the second half of the reverse stroke, BG1 conducts in the forward direction; in the first half of the reverse stroke, BG1 works in the reverse conduction. The reverse conduction voltage of BG1 comes from the high induced voltage of the field deflection coil during the reverse stroke, establishing one of the conditions for reverse conduction; the positive bias of the collector is the action of the bootstrap capacitor C2.

Malfunction Resolution:

Through live measurement, it was found that the field oscillation stage and excitation stage were working normally, the output stage BG2 was working normally, but BG1 was not working. Measurement of BG1 tube and its bias circuit components showed no abnormalities. Because the malfunction phenomenon is intermittent, it is a soft failure, and component measurement may not be able to find the fault point. It is estimated that the bootstrap capacitor C2 has a problem. After replacing C2, the equipment returned to normal.

4、Malfunction Summary

The fact that BG2 can conduct normally during the latter half of the forward scanning stroke, and the observation of a scan line with a lower brightness of approximately 0.5 cm wide below the horizontal band of bright lines also illustrates this point. During the latter half of the forward scanning stroke, only a small portion is due to the coupling capacitor C1 between the output stage and the deflection coil under normal circumstances. Under normal circumstances, it charges during the first half of the forward scanning stroke at a supply voltage E of 13 V, and discharges as the deflection coil power supply when BG2 conducts during the second half of the forward stroke. However, since BG1 is not working, the actual capacitor charges at a voltage lower than E/2, which is caused by the small current during the discharge of the deflection coil when BG2 conducts.

The main function of the bootstrap capacitor C2 is: during normal scanning operation, the excitation signal time is short and the change is fast during the first half of the reverse stroke, causing the deflection coil to generate an induced voltage of about 13 V higher than the supply voltage. The emitter voltage of BG1 is much higher than the collector voltage. After the bootstrap action of C2, the base voltage is also higher than the collector voltage, the collector is positively biased, and BG1 conducts in reverse saturation. The deflection coil and C1 discharge to BG1 and the power supply (first half of the reverse stroke). When the voltage across the deflection coil and C1 is consumed to E/2, BG1 conducts in the forward direction (second half of the reverse stroke). When C2 is malfunctioning, the above-mentioned process cannot be completed.

5、 Discussion

The basic principle of the display of this model of portable ultrasound detector is not complicated. For the repair of this type of fault, there are two key points:

① Quickly locates the general module through the fault phenomenon. The fault analyzed in this article is quickly judged through the fault phenomenon, and the fault point may be the display field scanning circuit;

② Being very familiar with the equipment circuit diagram helps to quickly eliminate and narrow down the fault range, and it also helps to correlate the specific circuit module with the fault phenomenon. Only by understanding the circuit diagram can accurate judgment be made and maintenance costs be saved. 

The fault described in this article belongs to abnormal ultrasound images. Generally speaking, in addition to the faults described above, common faults in ultrasound detection systems also include host faults, ultrasound probe faults, and abnormal shutdowns.When faced with different faults, we must first systematically analyze the fault phenomenon, then use the elimination method to gradually narrow down the fault range, and finally repair and solve the fault. At the same time, in daily work, regular maintenance and quality control maintenance of ultrasound equipment should be carried out, and ultrasound users should be regularly trained to standardize the use process and reduce the negative impact of ultrasound system failures on patient disease detection.

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