1, maintenance points
1.1 switch on the power supply for medical equipment
Before the repair, must be familiar with the basic working principle of cable joint, and can read circuit diagram, and then according to the switching power supply function will be divided into several basic units, and then draw out the framework, as the main reference for fault repair, this helps to quickly identify the causes of the problem. In order to accurately determine the fault location, is conducive to improve the speed of maintenance.
1.2 in the process of maintenance, can load on the output switching power supply board, access to a false, such as high power resistance, it can eliminate load fault influence on switching power supply, can also relieve the light load protection, but also can effectively avoid the switch damage due to saturation time is too long, the most important is, in the process of maintenance can prevent output voltage caused by high load damage condition.
1.3 in the overhaul of the switching power supply, the power board should first observe, to see whether there is obvious damage to components, insurance check again, then, to see whether the fuse, leakage or damage resistance etc., after completion of the above steps, can cause damage to components analysis the specific cause of the failure, to take effective methods for maintenance. Using this method to repair the switching power supply can not only accelerate the speed, but also simplify the process and improve the efficiency of maintenance.
The first 1.4 power, then the output voltage of each measurement, if the voltage is normal, indicating that the switching power supply is normal, the load circuit failure; if an abnormal output branch, you can determine the fault occurred in the branch, then only need to repair can eliminate the trouble of the branch, the switching power supply restoration work. Special attention is needed, the working frequency of the switching power supply of medical equipment are in the tens to thousands of Hertz range, so you can't use the ordinary tube instead of pulse rectifier, if the output voltage is low or high, it should be regulated for the checking circuit of the power supply, including amplifying circuit, a coupling circuit, sampling circuit and the modulation circuit etc..
1.5 if all the output voltage is low, it should be the first to measure the collector voltage of metal cable connector switch, if the voltage up to 300V, so that a component of the rectifier filter circuit power, the damage, the general replacement of components can be eliminate failures. Special attention is needed to replace the fuse in the front, should identify the specific reasons leading to fuse, if short circuit fault caused by the fuse, need to eliminate the short circuit, or even replace the fuse, fuse the risk also exist. Because the filter capacitor failure is relatively hidden, especially in its capacity is reduced, the collector voltage drop is not obvious, the use of multimeter is difficult to accurately determine, using the oscilloscope can intuitively observe problem, this is because in the case of AC component will significantly increase.
1.6 if the collector voltage of the switching power supply is normal, then the switch tube should be detected with emphasis. It is necessary to replace the fault caused by the damage of the switch tube. Before switching, the switch circuit protection circuit should be carefully checked, so as not to cause damage to the switch tube due to the failure of the protection circuit. At the same time, the load circuit should also be checked to eliminate the overload damage of the switch tube due to the load fault. In addition, in the maintenance, we should take full account of the pulse width modulation circuit protection, such as start protection circuit, voltage regulator protection circuit.