Changhong LCD TV LED32770X accessories leakage between the special fault examples - appliance repair

Electronic scale crystal oscillator 3.2*2.5mm 3225 16M (16.000MHZ) 12PF 10PPM 20PPM 30PPM

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

Factory direct 0805 blue light patch led

Inductance

SMD aluminum electrolytic capacitor

I encountered a strange fault with a Changhong LCD TV model LED32770X. It was repaired the day before yesterday, and the issue is related to leakage between the pins of some components. The symptoms were that the power-on indicator would flash but the TV wouldn't turn on. Sometimes it would work for a minute or two and then shut down, and other times it would function normally without any issues. After disassembling the unit, I measured the voltages: +5VSTB was at 5.2V, ON/OFF was at 4.4V, which suggests the motherboard is powered on. However, the 24V line was at 0V, which is abnormal. Checking U401 (1275A), the voltage on the 6th pin was 0V, while U402's K pin was at 14.4V, A pin at 0V, and R pin at 0.44V. U402 is a 431 precision reference, and the R pin should be around 2.5V. Since it wasn't, I assumed there might be an issue with the protection circuit due to low input voltage. All resistive components checked out fine, but I couldn't find the schematic online. However, I found a similar repair case where the problem was with U402. I tried replacing it, and after removing it, the issue was resolved.
There was a thin layer of something on the R and A pins, which looked shiny—possibly from ionization or oxidation.



Has anyone else experienced this kind of issue? I remember that Sharp remote control receivers used to have similar problems, where they would sometimes respond and sometimes not. This type of repair was also posted on this forum, but I’m not sure how to share the link here.