Rencheng Repair Case: A Case of Handling a Burning Smell from a Philips EPIQ 7 Ultrasound Machine

Machine Type: Philips Color Doppler Ultrasound Diagnostic Instrument

Machine Model:Philips EPIQ 7

Fault Phenomenon
After the EPIQ 7 ultrasound diagnostic instrument had been operating for 4 hours, the ultrasound doctor discovered a burning smell emanating from the machine, but the display screen showed normal operation, and all machine functions were normal.

(1) Check the ultrasound instrument's main power supply module:
The power supply of this machine is different from other cart-type ultrasound diagnostic instruments. It has both AC and DC power supply modes. The host can be connected to AC power for operation, and in the event of a power failure, it can also be powered by the built-in battery for 0.5 hours. The power supply unit is installed in the lower rear part of the bottom of the equipment. The power indicator light can be seen, and the battery box can be seen after opening the cover.
The two power modules were removed from the power box. The battery had no odor. After testing, they were directly connected to a 220V AC power supply, and the output voltage of each group was measured and found to be normal. With the power cord plugged in, a digital multimeter was used, set to the AC voltage range of 750V, and the AC output voltage was measured, which was normal.
(2) Check for PC-side faults:
The side panel of the ultrasound instrument was opened. The PC module is an independent chassis. After removing it and opening the PC module chassis, it was checked that the above-mentioned logic power supply unit was intact and odorless. The CPU, integrated circuits, heat sink fan, and discrete components such as resistors and capacitors on the motherboard were all in good external condition. Each voltage was measured using a multimeter and found to be normal.
(3) High-power power connectors:
The high-power power cable connectors were checked and no abnormalities were found. The contact of the plug and socket was good. Because the shutdown time was long and the instrument casing was disassembled, the burning smell had weakened. After communicating with the doctor, it was found that the smell was slightly stronger near the instrument panel. The structure of this instrument panel is shown in Figure 1.

Each button on the operation panel was operated to check the corresponding function. When adjusting the time gain compensation slider (because the slider corresponds to different depths of ultrasound imaging, it is also called the depth gain compensation slider), it was found that the third slider from the far end did not change the grayscale on the ultrasound display screen when it was slid left and right. When adjusting the other gain compensation sliders, the grayscale display changed from dark to bright, indicating that this button was malfunctioning.
The gain compensation slider is a continuously variable sliding potentiometer. Its function is to make echo signals of the same nature but different depths reflect the same amplitude on the same interface display, and the situation where the reflected wave is weak due to attenuation of the ultrasonic wave during propagation is compensated accordingly. The operation panel was disassembled, and the gain compensation 8-segment slider circuit constitutes an independent circuit board. The position corresponding to this key was found, and a burning phenomenon was found at the solder joint of one end of the sliding potentiometer on the circuit board, suspected to be the source of the odor. The circuit signal diagram is shown in Figure 2.

Measurement with a voltmeter showed that the voltage at the sixth point was 0V, and the voltage values at other points were normal, so this fault was determined. The gain compensation circuit board was replaced, the slider control display was normal, and no burning smell was detected after continuous use.
Summary
Poor contact of instrument connectors can lead to poor signal transmission and high resistance, resulting in current generation and heat generation. Continuous action can cause carbonization of nearby circuit boards and cable sheaths, or damage to components due to excessive current, producing a burning smell. This type of fault is easy for users to detect. If there is no odor, it is difficult to detect the fault, eventually leading to a short circuit of the circuit board and causing greater damage.
The cause of this fault was a malfunctioning set of operating sliders on the instrument panel. In the past, we have also encountered faults in buttons or sliders on the operation panel, such as malfunction or poor contact, but we have never encountered a situation where the contact resistance of the line terminal was too high, resulting in continuous overheating and scorching, because the power of these components themselves is very small, and the current passing through is also very low, making it difficult for a similar fault to occur. Therefore, this repair took a considerable amount of time to troubleshoot faults in the high-power power supply section, and did not consider the operation panel too much, and did not think it was caused by the gain compensation slider.
In addition, once a burning smell or other odor is detected from the equipment, even if the display interface and functions are normal, timely inspection and troubleshooting of the odor source should be carried out to eliminate hidden faults. Do not take chances. If not handled, continued use may cause a small problem to develop into a major fault.