Why do the monitors exhibit different capacitance bulging?
There are two Samsung 943N LCD monitors that are faulty.
The first indicator is not lit after power-on, and the standby button does not respond. Power-on detection of two-in-one board switching power supply primary +300V voltage normal, measuring secondary DC output are 0V, detection found +5V voltage output filter capacitor C201, C202 (1000μF / 10V × 2) top drum kit, after replacement test machine troubleshooting.
The second unit is the power-on indicator, but the screen is lit and black. Open the case and check that the +5V output filter capacitor is intact (using 1000μF /25V, which is different from the first one), but there are four other capacitor drum kits. It is checked that the +15V voltage output filter capacitor C206～C209 (470μF /25VX4).
Why do the same displays have different capacitor bulging at the same time? After analysis, the withstand voltage of the first display +5V filter capacitor is 10V, and the withstand voltage of the second display +5V and +15V filter capacitor is 25V, so the second display +5V filter capacitor is intact, but the +15V filter also selects 25V The pressure resistance is "small".
Through the maintenance of two Samsung 943V liquid crystal displays and the selection of other electronic and electrical filter capacitors, the general relationship between the rated withstand voltage of the filter capacitor and the applicable voltage is summarized: the power supply filter of 5V or less should use the power supply voltage for more than 3 times. Filter capacitor, 6V ~ 17V power supply filter should use power supply voltage more than 2 times withstand voltage filter capacitor, 18V or more power supply filter should use the power supply voltage 1.5 ~ 2 times the withstand voltage filter capacitor, see the table below.
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