A few days ago, I worked on repairing a Konka LED26F3300CE LCD TV. The issue was that the TV would start up with a normal image and the remote control worked fine. However, after about 10 minutes, the screen went blank, displaying vertical color bars, noise spots, and the speaker emitted strange noises. The remote control also stopped working. Initially, I suspected that the main chip's power supply had dropped suddenly.
After disassembling the TV, I found it used a 3-in-1 motherboard with version number 35017209. The switching power supply provided two voltage outputs: 76V for the LED boost circuit and 12V for other components. The 12V was then stepped down to 5V by N802 (FR9888), DC-DC modules, and further regulated to 3.3V, 2.5V, and 1.22V using various LDO regulators like N80 (W33J), N810 (1117-25C), N808 (1117-33C), and N801 (HL20B). All these voltages remained stable during the fault, which suggested the main chip’s power supply was functioning properly.
Next, I considered the possibility of a crystal frequency drift in the main chip, which can cause unusual faults. I replaced the Z501 27M crystal and its matching capacitors. However, the same issue returned after 10 minutes of testing. I then suspected a solder joint issue on the main chip N501 MT8227AAKU. Using a magnifying glass, I checked each pin but couldn’t find any signs of a cold solder joint.
At this point, the repair felt like a dead end. But I decided to re-examine the symptoms more closely. The problem seemed similar to a faulty connection on the DDR clock line, even though the TV didn’t have an external DDR module. I wondered if the main chip had built-in DDR and whether its grounding was connected through the heat sink at the bottom of the chip.
I flipped the motherboard and applied a small amount of solder paste to the bottom of the main chip. Then, I used a soldering iron to add a little tin to the copper foil beneath the chip. I moved the iron back and forth to evenly heat the area, allowing the solder to flow through the via and onto the heat sink. After cooling, I tested the TV again. It ran smoothly for 10 minutes, and after a full day of testing, the fault never reappeared. I concluded the issue was resolved.
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