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QHxservice manual download site
As for grating line extension according to the working time, the reason may be colorful display internal circuit (key should be suspected line output power automatic voltage regulating circuit) the low temperature characteristic of some components, as the work time extended, internal temperature rise, stable performance, slow drift caused by power supply voltage. QHxservice manual download site
QHxservice manual download site
Line output power load ability is bad, is usually caused by a power larger internal resistance. As shown in figure 3 lines of output power automatic voltage regulating circuit of rectifier diode D71O positive resistance increases, filtering capacitor C705 capacity drop or even failure will lead to the power resistance increases, the ability to load variation. And switch oscillation pipe (or the power adjustment) Q701 VC3842 control circuit integration block and the two key element performance deterioration will cause power automatic adjustment ability to drop, deterioration in the power load capacity. QHxservice manual download site
D701 first, C705 and Q701 one by one in new, fault is still. Then after VC3842 change new, fault elimination. After the event will be the original product VC3842 product VC3842 online measurement data and comparison, found that two integrated block most of the pins of the same data, only VC3842 (6) feet output signal voltage have difference: new product is + 3.9 V (the original product is + 3.5 V), the product output signal voltage amplitude than the original product is bigger, that is to say new VC3842 control of the switch oscillation tube Q701 adjustment ability is stronger, or the original product electrical performance degradation, lead to the control of Q701 weak, resulting in line output power supply voltage of the load capacity, grating lines with image brightness change caused change of fault. And in the strength of the new integrated block VC3842 stability is better than the original product. Because integrated block VC3842 after change new line grating image extension according to the working time of fault is eliminated. Combined analysis of the two faults of colorful display phenomenon is due to the performance of the control circuit integration block VC3842 caused variation.
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