Heraeus Biofuge Stratos refrigerated centrifuge Internal paste troubleshooting Guo Jian, Gao Yanyan (Laboratory Instrument Factory, Academy of Military Medical Sciences, Beijing 100850, China) In medical research, centrifuges are commonly used experimental equipment. Heraeus Biofuge Stratos refrigerated centrifuges have the advantages of automatic rotor recognition, electronic imbalance detection, and extremely high acceleration and deceleration performance. They are highly versatile desktop centrifuges of the same kind. Machine [1]. In the practice of repairing this centrifuge, I gradually explored and summarized some experiences, and now I combine a troubleshooting example to share with my peers. 1 Fault phenomenon User Description: After turning on the machine, there is no abnormality in the rotation. But after turning on the cooling, you can smell the smell from the machine. 2 failure analysis It is intuitively judged that the refrigeration system is faulty, and it may be damaged by one of the components such as the compressor, the compressor starting capacitor, and the cooling fan. However, according to the statistics of maintenance records in recent years, the refrigeration system of this centrifuge is perfect and not easy to malfunction. Therefore, the troubleshooting idea is: the compressor of the refrigeration system, the cooling fan and the main control circuit are separated, and the 220V AC voltage is separately supplied. Can work properly. After the separate power supply test, the compressor and the cooling fan can work normally, and there is no problem in the refrigeration system. After removing the main control circuit board in the chassis, carefully check it, and no obvious burnt and black marks [2] were found. No abnormalities were found in the measurement of motor windings and insulation. Measure a 75Ω high-power resistor behind the fan (brake resistor, actually two 150Ω resistors in parallel), and the resistance and insulation are also normal. According to the description of the fault phenomenon, it is suspected that the braking resistor is continuously energized when it is not energized, resulting in overheating, thereby causing a paste smell. Figure 1 Schematic diagram of the brake circuit As shown in FIG. 1 , the working process of the braking resistor is: the standby state of the centrifuge and the speed rising and the centrifugal phase of the motor, and no current flows through the resistor; when the centrifugal stop is stopped, the rotating speed of the rotating head decreases, and the motor is in the deceleration braking state. The feedback voltage of the motor returns to the DC network, causing the DC voltage P+, ​​which should be at 310V, to rise. If the voltage value is too high, it will result in The inverter circuit is damaged. In order to protect the inverter circuit, the centrifuge has specially designed a brake circuit including a braking resistor. When the DC voltage P+ rises to a certain value, the comparator output signal drives the IGBT tube BUP304 to conduct, so that the excessive DC voltage is released on the braking resistor [3]. Therefore, it is suspected that the comparator and the IGBT tube of the brake circuit may be damaged. 3 fault finding Use a multimeter to test the vulnerable components of the main control board online: IGBT tubes, diodes, high-power resistors and other components, and found that the cement resistance (4.7Ω/10W) is damaged, and the C and E pins of the IGBT tube BUP304 are short-circuited. As shown in FIG. 1, after the centrifuge is turned on due to the short circuit of the BUP 304, the DC voltage P+ is directly applied to the braking resistor, and the resistance continues to generate heat. When the refrigeration compressor is started, the cooling fan starts at the same time, and the paste smell generated by the continuous heating of the braking resistor is blown out, so the user reports that the smell is only smelled when the cooling is started. 4 Troubleshooting After replacing the new 4.7Ω/10W resistor and IGBT tube BUP304, the test machine, cooling and rotation are normal. In order to determine whether the brake circuit can work normally, I soldered two leads between the large capacitors P+ and N- of the DC network, connected to the voltmeter for monitoring, and a series of 68K was connected in parallel at the terminal of the braking resistor. /2W resistor LED, as shown in Figure 1. Start up, use the clamp meter to measure the standby current of the whole machine is 0.27A, the voltage value of the DC network is 310V, set the speed of 12000r/min, start, observe the change of the DC voltage of the network, and find that the voltage value decreases slightly during the acceleration phase, waiting for the speed After rising to the set speed, it returns to 310V. During this time, the LED is not lit at all, indicating that the brake IGBT tube is not conducting, and no current is passed through the braking resistor. Press the "Stop" button, the centrifuge motor starts to decelerate. At this time, the DC network voltage is gradually increased from 310V, and the stability is no longer rising until 340V. At the same time, the LED is bright, indicating that the brake circuit is working, waiting for the speed to drop. When it is below 2000 r/min, the voltage returns to its original value and the LED is extinguished. This shows that the brake circuit is working normally. In the test machine, I found that the relay K3 connected in parallel with the 4.7Ω/10W resistor is connected at the moment of starting, and my maintenance note records: the resistor is a current limiting resistor, which should be closed after the lid of the centrifugal chamber is closed. After the cover should be released, in order to find out the reasons, and carefully measure the relay control circuit, found that the control coil of the patch transistor BC817 between the C and E feet only 40 ohms resistance, replaced with a new transistor, returned to normal. If this fault is not found, although it does not affect the use, the inrush current at the time of booting easily breaks through the rectifier circuit. The whole machine is continuously tested, and no paste is released, and the fault is solved. 5 Summary experience 5.1 When repairing the instrument, look at the essence through the phenomenon, find the cause from the root, and do not be easily misled by some appearance. In this case, it is easy to determine that the refrigeration system is faulty, but the root cause of the problem lies in the main control circuit. 5.2 When repairing the instrument, it is necessary to understand the functions of each part of the circuit board, and how to connect and work with the peripheral components, and use the method of elimination one by one to gradually narrow down the troubleshooting range. 5.3 Inspect the board, and prioritize the inspection of the associated parts of the consumables and consumable parts. 5.4 It is necessary to use the monitoring means consciously to judge whether the function module is normal or not. In this case, I use LEDs to monitor the working process of the braking resistor, which is simple and clear and very practical. 5.5 Develop the habit of recording maintenance files and statistical failure rules [4]. Since I have repaired this centrifuge before, and accumulated the working principle and part of the circuit diagram of each part, the maintenance progress is very smooth and convenient. [references] [1] Zhao Xiaoguang. Key Technology and Progress of Benchtop Centrifuge[J]. Modern Scientific Instruments, 1999(4): 13-15. [2] Tan Changsheng, Wei Jiri, Zhang Chunxia. Thoughts and Methods for Troubleshooting Instrument and Equipment[J]. Medical Equipment Information, 2003, 18(11): 59-61. [3] Zhang Yanbin. Xiao Sunxue Frequency Conversion [M]. Beijing: China Electric Power Press, 2010: 105-119. [4] Wang Kebing, et al. Analysis of the causes of high failure rate of medical equipment and countermeasures [J]. Medical and health equipment, 2012, 33 (2): 111-112. Active Pharmaceutical Ingredients Product categories of Active Pharmaceutical Ingredients, we are specialized manufacturer and distributor from China, we have the perfect after-sales service and technical support. 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