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 unique fault with a Changhong LCD TV model LED32770X. The unit was repaired the day before yesterday, as shown in the images below. The issue is that the power-on lamp flashes but the TV doesn't turn on. Users mentioned that sometimes it works for a minute or two before shutting down, and other times it operates normally without any issues. After disassembling the unit, I measured +5VSTB at 5.2V and ON/OFF at 4.4V, which suggests the motherboard is powered on. However, the 24V line was reading 0V, which is abnormal. Further testing showed that U401 (1275A) had 0V on all pins, while U402 (K pin) had 14.4V, A pin 0V, and R pin 0.44V. Upon analysis, U402 is a 431 precision reference. Normally, the R pin should be at 2.5V, and the K pin should be active. However, in this case, the circuit seemed to be in a low input voltage protection state. I checked all resistive components, and they were within normal ranges. Unfortunately, I couldn't find the schematic diagram online, but I found a similar repair case where the problem was traced to U402. I decided to replace it, and that resolved the issue.




I'm wondering if others have experienced this kind of issue before. I remember that Sharp's remote control receivers used to have similar problems—sometimes working remotely, sometimes not. This type of repair has also been discussed on this forum, but I don't know how to share the link here.