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 TV fails to light after the second boot and shuts down due to protection. Upon disassembly, it was found that the screen is a Samsung V3 plasma panel. To identify the issue, the screen was checked first, and no light was observed. During normal self-test, the screen should display a uniform white grid. This indicates a defective plasma screen assembly. At the time of self-test, LEDs LED8001, LED8002, and LED8003 were all on, while the logic board's indicator light flickered on and off. The VS, VSCAN, VSET, and VE voltages were measured but showed no voltage. The VA voltage was initially over 90V and then dropped to 0V, which should normally be around 70V. This suggests a poor regulation in the VA circuit. Further inspection revealed that the VA regulator consists of IC8025 (a diaphragm IC), TL431 (a three-terminal precision voltage regulator), and surrounding resistors and capacitors. The voltage at R8134 was abnormal, with the photodiode’s positive terminal showing -0.24V instead of a positive value. After checking the F/B-VCC circuit, it was found that resistor R8129 had no voltage on both ends. This indicated an issue with the F/B-VCC circuit. Upon further inspection, D8015 was found to be open. Replacing it with a new IN4148 resolved the problem. 2. Changhong PT4206 (B) plasma TV shows a purple grid after the second boot and shuts down. Disassembling confirmed the screen is a Samsung V3 panel. Testing during self-test showed LED8001, LED8002, and LED8003 lit up, but the screen displayed a dim purple grid. The VE voltage was measured at 0V, indicating a short to ground. After removing CN8002, the load on the board was not shorted, but the power board still showed a short. Further inspection revealed that D8044 was damaged. Replacing it with a new RU3C fixed the issue. 3. Changhong PT4206 (B) [Samsung V3] plasma TV has a yellow indicator light after the second boot and eventually enters protection mode. Upon disassembly, LED8003 was lit, and after the second boot, LED8002 and LED8001 lit up, with the relay making a sound. However, the screen remained dark, and after a while, LED8004 turned red, causing the machine to shut down. During the self-check, components on the screen were identified as faulty. The power supply sequence involves T8001 generating VSB (+5V), which powers the CPU on the main board. When the power-on command is issued, the CPU sends a low-level signal to the power board, activating the relay and PFC circuit, producing around 400V. The switching circuit generates VA, VCC, D3V3, and D5VL voltages, which are sent to the logic board. If any voltage is abnormal, the CPU triggers protection, lighting LED8004. In this case, the logic board did not receive proper power, and D5VL was measured at 1.34V instead of the expected 3.3V. After replacing IC8026 (LM2576T-ADJ), D5VL returned to normal, and all voltages were restored, fixing the issue. 4. Changhong PT4206 (H) [Samsung V3] plasma TV has no indicator light. The LED8003 was not lit, indicating a power issue. After checking, fuse F8001 was good, but capacitor C8017 was bulged. Replacing C8017 and F8002 did not fix the issue. Further testing showed that F8002 was open, and after replacing IC8003 (TOP223PN), the fault was resolved. 5. Changhong PT4206 (H) [Samsung V3] plasma TV has no relay sound after the second boot. The indicator light was on, suggesting the motherboard was powered. Testing the RELAY signal showed it was working properly. By shorting J8005, the LED8002 and LED8001 lit up, confirming the relay was functioning. However, the relays RLY8001 and RLY8002 were not pulling in. After checking the transistors, Q8009 was found to be faulty. Replacing it restored normal operation. 6. Changhong PT4206 (H) plasma TV has no indicator light and the screen is dim. The screen was tested and found to be non-functional. LED8003 was not lit, indicating a problem with the power supply or VSB circuit. Testing showed that F8002 was open, and D8007 had a shorted diode. Replacing these components restored the TV to normal operation. 7. Changhong PT4206 (B) [Samsung V3] plasma TV lights up after boot but the screen remains dark. During self-test, LED8003 and LED8002 were lit, but LED8001 was off. Testing showed the PFC circuit was not working, with T-VPFC voltage at 0V instead of 400V. After replacing R8010, the issue persisted, and Q8005 and Q8008 were found to be off. Replacing the PFC diaphragm HIC8001 resolved the problem. Maintenance Tip: Plasma screens have strict voltage timing requirements. For easier troubleshooting, observe the indicator lights on the power and logic boards. LED8003 indicates VSB power, LED8002 indicates PS ON, LED8001 indicates PFC, LED2000 indicates logic board power, and LED8004 indicates protection. Use test points like J8005 and J8002 to simulate signals and isolate faults.