The maintenance experience of the lcd power source for servicing the lcd panel is set out in article 1, when overhauling the lcd power source, first confirming the condition of the safety tube, which is intact, and normally the switch in the pfc correction circuit, etc., has not failed. A further measurement of the presence of short circuits to the ground of large electrolytic caps, with more than tens of thousands of euros of charged resistance indicating that the power supply was not punctured. If the tube is damaged, the first check the pfc correction circuit switch and the second check the secondary ic。
General output +5v, +12v, +24v voltages less than 40 inches; general output +5v, +12v, +18v, +24 v voltages greater than 40 inches. Of which +5 v is for stand-by voltage, +12v for digital panels, +18v for acoustics, and +24 v for backlight panels. In practical maintenance, power panels of the same voltage and power can be replaced。
Iii. Power belt load capacity differentials, starting with a test of whether the pfc voltage is normal (380 v), and if so, the problem is caused by the power thick membrane, usually the power thick membrane carrying capacity differentials, which are noted。
Iv. Thermal fields are thermal on the power panels, with yellow triangles marked with heat-spreads and circuits beneath them. Strict direct hand contact! Note that no detection equipment can be directly connected between the hot and cold
5. The power panel can be removed from the television for independent maintenance, which requires only the switch control of the circuit triode c, e short-linking (or the connection of an electrical barrier of about 1. 5 k to the secondary power source's +5v output end) and the whole machine is in a state of operation with the output of all circuits. In part of the lcd switch, the main switch is operating in a normal state only if the +12v or +24v output end carries a load of some power. So on the +24 v output end you can fake a 36 v light bulb for an electric bike (or a motorcycle light bulb for a +12 v output end)。
After the liquid crystal power source has been powered, the secondary power source works first to output +5v voltage to the cpu on the panel, at which point the whole machine is on standby. After pressing the " stand-by " button, cpu output the switch level, the pfc circuit works first, converting +300v pulse current voltage to normal direct current voltage (+380v), the main switch power pulse wide oscillator starts work, followed by the primary switch transformer secondary output +12v, +24v voltage, and the whole machine enters normal working condition。
7. Protection of circuits, which, in addition to commonly available peak absorbor protection circuits, are located in excess of +24v, +12v and +5v voltage, overload protection circuits, which are more protected by 4 amplifiers lm324, 4 voltage comparator lm339, 2-voltage comparator lm393 or 2-calculator lm358. Overflow protection circuits may be removed during maintenance and, if the voltage returns to normality, indicate which path is responsible for the break-up. Then we'll do the repairs。
8. Prior to the opening of the aircraft, confirm the presence of explosives, electric drum packs and, if necessary, replace them and measure them all. It is recommended that when all damaged equipment is replaced with a test device, it would be preferable to remove the original fuselage and attach a 220v/100w light bulb, which would effectively prevent further blasts。
What's a pfc circuit? The pfc circuit is said to have whited up the +300v voltage of the bridge pile to +375v - +400v. This is also the first point where the lcd tv power is different from the crt, the second point of the difference is that the secondary voltage is lower than the crt, and the rest is the same as the normal switch power. The measurement of large filter wave capacity of 330 u/450 v at two end voltages of +375 v-------+400 v indicates that the power factor correction of the circuits is normal; if both end voltages of the capacitation are measured at +300 v, the pfc circuit is not working and the pfc oscillation integrated circuit is inspected。
X. The main switch voltage +24v or +12v output currents are large, the requirements for the whole-stream diodes are high, with the general use of low-pressure-difference high-power shortki diode tubes, which cannot be replaced with ordinary whole-stream diodes. On the other hand, after the load, the voltage rises, mostly due to poor filtering of the power source。
Power source maintenance methods for the lcd tv. We are all more sensitive to the bomb machines, especially when we see the sma-e1017 blow, the fqa24n50 go through, and we are nervous, and i am afraid that the next time we turn on, there will be a risk that these elements will explode again, even if we do not know how to fix it。
With regard to how such failures should be repaired, i think some of the following points can be made: first, an analysis should be made of the cause of the bursting of a metaware device, and why is the field effect tube of the pfc circuit pierced? There are two reasons for this:
1. Effect overflow
2 the field effects are over-pressured. We know it's gonna get damaged, right? Because two pn knots pierced during the flow, more often because of the excessive length of the ton cycle and the damage to the field effect tube at the end of the period. Why? In switch circuits, the charge pole of the switch, coupled with absorption circuits, reduces the high pressure that occurs when the switch is closed, the size of the voltage is proportional to the current rate of change (corresponding to di/dt)。
So when the switch is closed, the counterpressure of the switch is high, and what about the power of the soft switch? The so-called soft switch is to reduce the power consumption of the switch to zero。
{we know that the mosfet switch is barrier-resistant and has a low resistance when saturated. During tablet maintenance, we find that irf 7314, the d and s ends of the mosfet tube, can't be reduced by our one-size-fits-all gauge, while the saturation pressure of the ordinary tripolar tube is down to 0. 3 v. For switch power using the effect tube, the switch tube is hot because the switch is severely depleted. Soft switches are zcs (zero curent switching zero current switch) and zvs (zero voltage switching zero voltage switch)。
Do you want to buy a switch!
