Samsung 710S monitor failure phenomenon is the power indicator is not bright. Open the cabinet, check the power supply part. It is found that the insurance tube intact, and there was no obvious damage to the components, there has been no obvious weld. The power supply of the machine is thick film KA2S0680, and the voltage of the starting pin is approximated by 0V. Obviously not normal. Suspected resistance R604 (180K) to start the resistance deterioration, remove the normal measurement, measuring R618 (1K) resistance is normal. The resistance of the IC601 to the ground (foot) is small, and only a few of the dozens of EU (pointer type meter measure, slightly different).
The circuit external only two components, a capacitor C617 and a regulator diode VD630 (the original does not mark the element). Down to the measurement, the regulator has been found to breakdown damage.
The power supply start condition is relatively simple, 300V power supply through the startup resistor R604 to charge the capacitor C614. Then through the R618 to start end provides working power supply, C614 at both ends of the voltage up to 18V or satisfy the thick film block starting requirements, thick film circuit. After power supply, the power supply of T601 is supplied by 8 ~ 7 windings of IC601.. There is an important element in the work of the thick film circuit, which is the capacitor C614. When the boot is started, the resistor is charged to it, and then it provides the power for the foot of the IC601.. When the C614 is normal, its voltage is raised from the process of charging with the Ov, and when the voltage rises to the 18V, the thick film circuit works.
If the thick film circuit does not work, then C614 charging voltage will rise further, to rise above 27V, zener diode VD630 up clamp effect, use IC601 3 feet voltage stability at 27V, lest IC601 damage. Check the internal circuit of 1C601 (see chart, circuit diagram from the network.) , its internal foot and there is a 32V regulator diode (circle), apparently the designer here added double insurance, in case of damage to thick film caused power other parts of the serious damage. So in what case, there will be no voltage rise, personally think there are two cases can occur. One is that IC601 has damaged the job, and the other important reason is that the capacity of C614 has changed..
Is not difficult to understand, if the capacity of the C614 is no capacity or open welding, then the boot instantly the foot voltage is high. The voltage of the foot can be much higher, and the parameters of C617 from the designer can be seen by the 100V, which is important for the protection of the thick film circuit at this time VD630.. Therefore, VD630 is not only a "appendix" element, but a "lymphatic" element for the protection of the circuit.. The VD630 like the car safety belt, when we obey the traffic rules, an accident does not appear when the seat belt without any meaning, but if there is a crash, the safety belt to drivers and staff of life played a active role in the protection of. In addition, VD630 27V regulator is more scientific, in order to increase the safety factor, once with 33V replacement, the individual feels undesirable. Because the lost inside the 3 feet of KA2S0680 regulator (32V) protection tube, if IC601 internal breakdown voltage regulator tube the, the thick pipe is damaged, beyond repair, natural to increase the maintenance cost. This not only did not increase the safety, but increased the risk.
The analysis can also know VD630 damage in addition to aging and the element itself, another important reason is that C614 capacity smaller, causing the boot immediately in the VD630 voltage high breakdown because of it. To verify your analysis, remove C614, and measure its capacity with a capacitance meter of only 3 F. After the replacement of VD630 and C614, repeated boot are normal.