Hisense LCD TV logic board troubleshooting example - appliance repair - Database & Sql Blog Articles

Symptom: The boot sound is normal, the backlight is normal, and the black screen has no image.
Fault analysis: the boot can start the backlight and have sound, the fault range has been reduced to the screen line, the logic board and the screen itself;
Disassemble inspection: The logic board power supply 12V is normal, unplug the screen line, and the screen is found to be special when booting. Different common power supply will turn white screen. The screen is still powered by black screen; use the multimeter to measure the logic board power supply. The resistance is in an open state. It is obvious that a fuse or power supply insurance is open, and along the printed circuit board, it is found that a patch insurance has been opened;

As shown below, the patch insurance is soldered next to the inductor in the upper right corner.


This is the little thing, the letter printed on it is UD, who can tell me how much current is the patch insurance?


Can burn the insurance generally have a short circuit, the first thing that is suspected is the patch power supply filter capacitor, this stuff is often a little trouble; carefully observe the circuit board, found that the circuit board in the lower right corner of Figure 1 has a capacitor on the upper end of the circuit board. Yellow, it is obviously caused by high temperature, CP2 under decisive welding, the measurement has been short-circuited;
This is the gadget below.


Then measure the 12V power supply part has no short circuit phenomenon, because the patch filtering of this type has been used up, there are N 12V patch filters on the lookup board, one more one is not much, and a small capacity is used. The chip capacitor is replaced, plus I really don't know how big the patch insurance marked UD is, directly replace it with a 0 ohm chip resistor. The maintenance result is as follows


Install the logic board, the boot screen returns to normal, and the repair is over.

PS: Who can tell me how the patch insurance looks at its rated current, this information is basically not found.