LCD TV power board repair focus and maintenance steps - android - Phones Developers

DFN1006 TP-RCLAMP3321P ESD Diode Low Capacitance

MOS power IC full range

Probe current voltage pin 420*4450 head diameter 5.0 over current current and voltage pin

SMD aluminum electrolytic capacitor

Tantalum capacitor

The popular LCD TV sets have similar basic structures despite the different screen sizes. The small screen power output is 5v.12v.24v; while the larger screen output is 5/12/18/24 volts. There are two major parts when troubleshooting a power supply board.
First, the high voltage part: PFC (power factor effect positive) circuit, this part of the circuit will rectify 220v AC into 300v, and then increase it to 400v.
Second, the low voltage part: 5v required for the standby circuit (partial movement is 9v); 12/18/24 volts of the output of the drive pulse circuit (pWM); output protection circuit (overcurrent, overvoltage, overload).
The main part of the power supply maintenance is the 400v part, which is vulnerable to high voltage; the second is the low voltage 12/18/24v part, which is damaged due to large power consumption and large heat.
When receiving a faulty machine, first of all, please understand the user's use environment. Conditions. The timing of the fault. Phenomenon. This is a very important first-hand information. It should not be underestimated. It is helpful for analysis, judgment and troubleshooting. Secondly, after opening the cover, it is not busy to do it. Firstly, visually check whether the capacitor has cracked the drum; high-power resistor, diode, triode, thick film block (integrated block), whether it is cracked or discolored, whether the connector and the cable are loose. Third, do not rush to blindly electrify, first use the resistance method to measure the fuse. Anti-overvoltage varistor components. Bridge stack, high-power components are open. Short-circuit (plug. Line. Total K and so on). The above looked at the inconspicuous, and half of the faults were accurate. Fourth, when the above inspection does not find a significant fault, the power can be detected.
a, check 5v standby voltage, which is a prerequisite for many movement power board work, common fault components have power integration block. Power switch. Current limiting resistor. Starting resistor. Regulator feedback component (optocoupler.TL431), rectification filter element.
b. Under the normal condition of 5v, use the dummy load (usually with 24v.75W bulb) to connect to the 24v output terminal (the light bulb is used to make the dummy load, one is intuitive. The second is to prevent the airborne self-protection), and then forced (simulated) to boot. Use a 1K (can also pass through) resistor to connect the 5v output to the ps-0N pin. After booting, check whether the 12/24v output is available. If there is no output, the next step is to measure the voltage across the pFC filter capacitor (typically 400v). If it is not normal, check the level of the integrated block, switch tube and so on.
c. The driving pulse circuit is usually composed of an integrated block, a switch tube, etc., and the consumable parts are mainly rectifier diodes and filter capacitors; the resistance is small and the power is large.
d. When the above circuit is repaired normally, the circuit can not work normally, disconnect the protection circuit. If the power output is normal, check the protection circuit and disconnect the protection components one by one. There are not many components, and the wearing parts are mainly regulated. Two-pole breakdown, small resistance increase, open circuit and so on. Inappropriate, and for reference. Thank you!