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Unvservice manual download site
Unvservice manual download site
Five, standby power supply, power switch tube D very rush absorbing circuit: IC851 switch tube in the globe, T880 primary coil can produce very high peak voltage, added to the IC851:7 feet, namely the power switch tube D, the high peak voltage will breakdown switch tube. To this end, on both ends of the primary coil T880 parallel to a peak voltage absorbing circuit: D892, R873, R886, C889. When these parts failure or open circuit, cannot absorb peak voltage, which may breakdown IC851. Unvservice manual download site
Unvservice manual download site
Six, mains under-voltage detection circuit: when the mains 220 v power supply voltage drops too low, because of the voltage stabilizing circuit automatically adjust action, to keep switching power supply output voltage constant, can make the switch tube guide through wide, electric current is too large, will damage the switch power supply, for the mains voltage protection circuit is designed. D885, C888 mains half-wave rectifier circuit, when the mains is 220 v, the voltage is 300 v, C888 after R884, R888, R894 partial pressure, on the R894 share 88 v voltage, the voltage to the two stabilivolt D884, D882 breakdown conduction, the two stabilivolt Q882 conduction, then Q882 C very 0 v, cause Q850 cut-off, Q850 C pole and IC851:1 foot, E grounding, Q850 deadline, has no effect on the normal work of the IC851. When grid voltage drop too much, such as lower than that of ac 100 v, R894 on pressure drop, voltage regulator tube D884, D882 cut-off, Q882 subsequently cut-off, IC851:5 foot 6 v voltage, the R854 to Q850 B, Q850 conduction, grounding the IC851 1 foot, IC851 to stop working, and protect the switch power supply circuit from being damaged. D857 is a voltage regulator tube, between IC851 1 feet to the ground, is a protection of voltage regulator tube, prevent voltage stabilizing optical coupling when that didn't work, the output voltage is too high. When the breakdown, leakage, reverse voltage regulator tube resistance decreased, can cause IC851:1 foot voltage drop, the switching power supply output voltage drop. Must pay attention in the maintenance.
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