Changhong plasma TV PT32600 repair column sharing - appliance repair - Huaqiang electronic network

0.8A 1000V rectifier bridge stack

Filter 18.432M

1, Changhong PT4206 (B) plasma color TV after the second boot no light, after a while to protect the shutdown. After disassembling, it was found that the machine is a Samsung plasma V3 screen. In order to judge the fault location, first check the plasma screen, the result is no light, the screen should be a uniform white grating during normal self-test. The description is that the plasma screen assembly is defective. At the time of self-test, it was found that LED8001, LED8002, and LED8003 were all lit. There is no voltage for measuring VS, VSCAN, VSET, VE, etc. The indicator light on the visual logic board is on and off after a while. The logic board is also working. The VS-ON control signal sent by the logic board is normal. The output voltage of the power board should be normal. When VA is measured, it is found that the voltage is more than 90V when it is energized, and gradually drops to OV after burning, and the voltage should be 70V when it is normal. The VA circuit is poorly regulated. Looking closely at the circuit, it is found that the VA voltage regulator is composed of a diaphragm IC8025 and a three-terminal precision voltage regulator block (IC8029) TL431 and peripheral resistors R8129, R8133, R8134, R8135R8138, R8142 and capacitors C8074, C8079, C8070. The R8134 has a voltage that is sent from the VA section. The positive terminal voltage of the photodiode is -0.24V. According to the normal circuit, this should be a positive voltage. It is estimated that this is not normal. Check the resistor R8129 supplied to the diaphragm for no positive voltage at both ends. Explain that there is a problem with the F/B-VCC forming circuit. After inspection, R8129 is connected to VSB (+5V) which is rectified by D8014 through D8015, and the indicator of the power of this unit is lit, indicating that VSB has voltage. The VSB was measured to be 5.2V. Guess is good. The negative end of D8015 is not short-circuited to the ground. In the road detection D8015 open circuit, after replacing with a new IN4148, the fault is eliminated.

2, Changhong PT4206 (B) plasma color TV after the second boot, no light, after a while to protect the shutdown. After disassembling, it was found that the machine is a Samsung plasma V3 screen. In order to judge the fault location, first check the plasma screen, the result is dim with purple grating, the screen should be a uniform white grating during normal self-test. The description is that the plasma screen assembly is defective, and has nothing to do with the motherboard and the AV board. Suspected that the power board or the maintenance board is defective. At the time of self-test, LED8001, LED8002, and LED8003 are all lit, and LED2000 on the logic board is also blinking. VS, VSC, etc. are measured normally, and VE voltage is 0V, VE voltage is not normal, VE is shorted to ground in the road detection, CN8002 socket is removed, the VE load on the board is not shorted to the ground, and the VE on the power board Short-circuit to the ground, carefully look for the components on the VE, only D8044 and C8071 (resistance generally does not cause a short circuit) may cause a short circuit, after disconnecting C8071 or short circuit, indicating that D8044 is damaged, replace it with a new RU3C after troubleshooting.

3, Changhong PT4206 (B) [Samsung V3] screen plasma color TV indicator light, after the second boot, the light becomes yellow, the whole machine is dull, after a while to protect the machine. Disassemble the machine and observe that the indicator LED8003 is lit. After the second boot, LED8002 and LED8001 are lit, and the relay has a sound. But the screen is not bright, after a while the red LED8004 lights up, the whole machine protection stops. In order to facilitate the maintenance, the self-checking machine determines that the components on the screen are defective. The voltage supply timing of the machine is as follows: After the power is plugged in, the switch circuit composed of T8001 on the power supply board works, VSB (+5V) is generated, the working voltage is supplied to the CPU on the main board, the CPU enters the working state, and the standby command is issued. At the same time, the green LED 8003 lights up. When we issue the power-on command, the CPU sends a low-level RELAY signal to the power board. At this time, the relay RLY8001 and RLY8002 pull in, the L8001 and the PFC circuit composed of the peripheral circuit work, and the PFC boost is about 400V. The voltage, at the same time, the green indicator LED8002 and LED8001 are lit one after the other. The switching circuit composed of T8005, IC8023 and peripheral circuits generates VA (+70V) voltage, VCC (+15V), D3V3 (3.3V) and D5VL (+5V). Among them, D3V3 and D5VL are sent to the logic board, the circuit on the logic board enters the working state, (at this time LED2000 will flash) sends a logic normal VS-ON (high level) signal to the power board. The VS-ON signal causes the VS voltage generating circuit composed of the T8002 and the peripheral circuit to enter the working state, and outputs an adjustable VS voltage of 160V~185V, and the voltage forms a VSE voltage through the T8003 and the peripheral circuit, and the voltage forms a VSC voltage through the T8004 and the peripheral circuit. This voltage forms a VE voltage via T8006 and peripheral circuits. The generated voltages are sent to the various components on the screen, and the components on the screen are electrically operated, so that the plasma screen is illuminated. If any of the voltages generated above are abnormal or overcurrent and are detected by the CPU on the power board, the CPU will issue an instruction to put the power into standby mode and illuminate the red LED 8004. After the machine is turned on twice, the relay has a sound of suction, and LED8001/LED8002 lights up, indicating that the motherboard has been working normally and a power-on command is issued. The indicator LED2000 on the observation logic board is not lit, indicating that the logic board does not get the working voltage or the operation is not normal. Test the D3V3 at F2000, which is normal. The D5VL at F2001 was measured, 1.34V, which was abnormal. Disconnect the logic board power supply connector and measure the voltage of the D5VL test point on the power supply board to 1.34V. It is still abnormal. Check the ground resistance and there is no abnormality. The D5VL DC/DC converter IC8026 has 1 foot of 17.5V, which indicates that the front stage power supply has arrived and should be normal. Debugging VR8009 adjustable resistor, the voltage gradually drops from 4.2V to 1.34V when booting. Abnormal, check external resistors R8143, R8145 and D8050, C8099, etc. No abnormalities. After replacing IC8026 (LM2576T-ADJ), D5VL voltage output is normal, VE, VSE and other voltages are also generated normally, and all lines are connected and restored to normal state. The whole machine returned to normal. (D5VL and D3V3 are both generated with LM2576T-ADJ, the only difference is that its external resistance is not the same)

4, Changhong PT4206 (H) [Samsung V3 screen] plasma color TV indicator is not bright, three no. The indicator light is off, indicating that the motherboard is not receiving power or the CPU on the motherboard is not working properly. Unpack the rear cover and find that the indicator LED8003 is not lit, indicating that the power supply is poor or the power supply is overloaded. Disconnect the power supply to the motherboard. Still not bright, indicating that there is a problem with the VSB voltage forming circuit. With the previous experience of repairing, we are much easier to fix. First check the fuse F8001 is good, visually found that the capacitor C8017 has a bulging phenomenon. The C8017 is just the filter capacitor of the primary part of the VSB voltage forming circuit. The test fuse F8002 is open circuit, the rectifier bridge stack D8007 is intact, and the drive block IC8003 has no abnormality in the road resistance. After replacing C8017 (450V/33UF0 and F87002 (1A), it is still not bad. After replacing IC8003 (TOP223PN), the fault is eliminated.

5, Changhong PT4206 (H) [Samsung V3 screen] plasma color TV indicator light, after the second boot, can not hear the relay sound. The indicator light is on, indicating that the motherboard has been powered. The fault may be caused by poor operation of the motherboard. The power-on test RELAY signal can change from high level to low level, indicating that the motherboard CPU has been working normally. To determine whether the motherboard's RELAY signal is sent to the main power board, directly short J8005, turn on the visual indicator LED8002/LED8001 or not Bright, indicating that RELAY has been normally generated, but it does not normally control the pull-in of relays RLY8001 and RLY8002. The fault should be on the circuit composed of Q8009/Q8013/Q8004/Q8006/Q8005/Q8008. Check the triode in the road. It was found that Q8009 was not normal. Remove the Q8009 (KTN2907A) test and found that B/C is extremely unreachable. After replacing with a good triode, LED8002 and LED8001 will be lit after power on, and the whole machine will return to normal.

6. Changhong PT4206(h) After the plasma TV is turned on, the indicator light does not light, and the screen is dull. After disassembling, it was found that the machine is a Samsung plasma V3 screen. In order to judge the fault location, first check the plasma screen, the result is no light, the screen should be a uniform white grating during normal self-test. The description is that the plasma screen assembly is defective. LED8003 does not light when the screen is self-testing. The description is that the switching power supply consisting of T8001 and IC8003 is defective. The F8002 (250V/1A) open circuit is detected, and the forward and reverse resistances at C8017 are normal. The forward resistance of the D8007 (S1WBS60) bridge stack is normal, but the AC input pin is shorted to the DC negative terminal, indicating that the diode in D8007 has a set of short circuits. After replacing the D8007 bridge stack and F8002, the whole machine returned to normal.

7, Changhong PT4206 (B) (Samsung V3 screen) after the boot light, the light can change after the second boot, but the screen is not bright, first self-test plasma screen, found that the LED 8003 and LED8002 on the plasma power are on, but LED8001 is not lit. The description is that the PFC circuit part or the circuit part composed of Q8005 and Q8008 is defective. Test the PFC boosted test point T-VPFC point voltage is 0V. Not normal, it should be 400V when normal. Indicates that the PFC is partially damaged or not powered. The second three anti-jamming circuits and D8003 are detected on the road. Found that R8010 is open. After the R8010 is replaced, the LED8001 is still off. Both Q8005 and Q8008 are in the off state. There is no voltage at the positive terminal of the IC8002 internal diode. It indicates that the PFC diaphragm HIC8001 is defective, and there is no RELAY-ON signal that outputs a high level. Troubleshoot after replacing the PFC diaphragm HIC8001. Maintenance Tip: As we all know, the plasma screen has strict requirements on the timing of voltage supply, and the order in which each voltage is established is strictly required. But this can be ignored for maintenance. We only need to know what conditions are generated by each voltage. For Samsung V3 screen power supply, we only need to look at the indicator light on the power board and the indicator light on the logic board to determine which voltage forming circuit has a problem: after plugging in the power, LED8003 will point. bright. If it is not lit, it indicates that there is a problem with the power supply of the whole machine or the VSB forming circuit. After the power-on command is issued, LED 8002 lights up. If it is not lit, directly check whether the RELAY signal is normally sent to the motherboard. Followed by LED8001 lit. If it is not lit, check if the AC220 is sent to the PFC circuit or the PFC circuit is working properly. When LED8001 is lit, the indicator LED2000 on the logic board will follow the flash. If it is not lit, it indicates that D5VL and D3V3 are bad. After the LED2000 is lit, the voltage of each group of the power board should be output normally. If it is not normal, check the VS voltage forming circuit and the VSET, VSCAN, and VE voltage forming circuits. In order to facilitate the repair and maintenance of the board. This power supply provides multiple sets of short-circuitable sockets to simulate or disconnect a portion of the circuit. Such as: J8005, when it is shorted, it can simulate the motherboard to send back the power-on signal. J8004, when it is disconnected, the protection detected by TV8001 can be released, and the protection is disabled. LJ8003, when disconnected, PANEL-POWER protection starts, the whole machine enters the protection state. J8002, when shorted it, can simulate the VS-ON signal returned after the logic board is working properly. zJ8001, after disconnecting it, it disconnects the power supply of the PFC and subsequent circuits, and it is convenient to judge whether the VSB part or the PFC part circuit is short-circuited. Let's talk about the role of the indicators on the screen assembly.
1. LED8003→VSB power indicator light should be lit when AC power is turned on. Otherwise, the whole machine power supply or VSB voltage forming circuit will be faulty.
2. LED8002→PS ON normal command status indication. If it is lit, it indicates that the power-on command issued by the main board is normal. If it is bad, check whether the RELAY boot command sent by the main board has reached the power board.
3. LED8001→PFC power supply works normally. This indicator will not light if there is a problem with the PFC power supply.
4, LED2000 → logic board power supply normal indication. If it is not lit, there is a problem with the D5V and D3V3 power supply forming circuits.
5, LED8004 → power protection action indication. Under normal circumstances, it is off. As we all know, any abnormality detected by the HIC8002 detection pin will protect it from lighting. We will eliminate it by the above indicator status and mastering working principle.