Changhong Jingxian Wang rear projection TV does not boot black screen fault repair example - Home Appliances

Probe domestic switch needle KG-300K with a head diameter of 3.0mm, normally open switch needle

1.5PF SOT23-6 Low Capacitance 5V Breakdown Voltage 6V SRV05

Filter 18.432M

Changhong Jingxian Wang back cast color TV does not boot and has a black screen. This repair guide focuses on the Changhong HP Jingxian Wang series rear projection color TVs using the PDT-3 movement. "No boot / black screen" is a common issue in this model. This article provides maintenance ideas for reference.

First, check if the power supply board is functioning properly by measuring the input and output voltages. If it's not working, check the 380V voltage across C810 (main filter capacitor). If that's not normal, inspect the PFC circuit and its preceding components. If the voltage is normal, verify whether NQ821 (STR6656) is operating correctly and whether the secondary outputs of the switching transformer—such as 8V, 5V, 22V, 12V, and +B—are within specifications. The system uses dual power supplies, so even if one group is faulty, the other may still function. However, if the 5V voltage is missing, the TV won’t start. A drop in 8V may result in a black screen, while an abnormal 12V can cause the main circuit to malfunction. The 22V is the line scan starting voltage, and without it, the TV cannot power on. Without +B voltage, the TV will also fail to boot.

During repairs, never remove the 8V power plug while the TV is powered on, as this could damage the projector upon re-powering.

If the +B voltage reads 0V, check the ground resistance at the +B output. This usually indicates a damaged output tube. The PDT-3 movement uses a dual scanning circuit, so you can test W034 to determine if either V404 (C5588) or V481 (C5143) is damaged. In practice, C5588 tends to fail more frequently. If both the switching power supply and the line output tube are working, measure the line excitation and oscillation signals. If the row drive is faulty, it may lead to the row output tube failure and subsequent burnout.

The line oscillating signal is closely related to NZ401 (TDA9111) on the main board. First, check the 5V and 12V power supplies to the IC, then confirm whether the horizontal and vertical signals are being output correctly from the chip, along with the bus voltages (SDA, SCL).

The bus signal of the PDT-3 movement is generated by the CPU board. When troubleshooting, first check if the 8MHz crystal oscillator is working, then ensure the 5V power supply is stable. Finally, test the U4 (W27C010-70) integrated circuit. Additionally, the 24C64 memory chip on the CPU board has a high failure rate.

The DPTV board’s bus signal directly affects its performance. If the bus signal is abnormal and the 8V power is unstable, a black screen may occur. Moreover, issues with the DPTV board can also lead to component burnout.

N20 (KA2500) is a pre-viewing IC. If it fails, especially without 12V power, a black screen may appear. The same issue can occur if the IC itself is faulty. NQ911 (TDA6120Q) is the final video display IC, and any malfunction here will also result in a black screen.

Finally, during the repair process, if the power indicator doesn't light up and no degaussing sound is heard, check the power board and scan board first. If the indicator is on but the TV doesn’t turn on, focus on the CPU board. If there is sound but a black screen, the DPTV board should be checked next.