Changhong color TV CHD25800 boot has a similar line frequency scream sound screen does not shine fault repair - android - Phones Developers

Single chip microcomputer STM32L151CCU6

Test - lowercase jpg

Mobile phone crystal 3.2*2.5mm 3225 26M (26.000MHZ) 7.5PF 10PPM 20PPM 30PPM

Kaixin micro test

Test probe P100-M3

Maintenance of Changhong color TV model CHD-2B and CHD25800. When the TV is turned on, it produces a high-pitched noise similar to a line frequency scream, and the screen does not light up. Using an oscilloscope, I observed the collector waveform of the boot tube and noticed it resembled that of a failed S capacitor (a similar issue was previously repaired by Changhong HD). After unplugging the deflection coil, the waveform remained distorted, which ruled out the possibility of a faulty S capacitor or deflection problem.

Online research suggested the issue might be related to the deflection coil, but after removing it, the noise still persisted. This led me to doubt the initial assumption. I continued to investigate further and eventually found the root cause. The problem was located in the deflection coil itself, where internal corrosion had caused a short circuit due to glue residue. Once this was addressed, the TV functioned properly again.

Summary: Although unplugging the deflection coil usually stabilizes the waveform, in this case, the waveform was still abnormal. It was unusual, but after careful inspection, the defect was identified and fixed. The repair process involved identifying the exact location of the fault, cleaning the affected area, and replacing damaged components.