Konka LCD TV LED46R5500DF no backlight failure repair - android - Phones Developers

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

Photocoupler

This machine was passed on by a friend. Before the image became dark, only one corner was visible in the later stage. After that, nothing showed up. I decided to open the cover for repair and found a three-in-one board. The LED supply voltage was measured at a normal 68V (with a lamp voltage of 49V after operation), which ruled out any issue with the AP3041. However, the IW7018 chip was extremely hot. Although it's expected to run warm, this temperature seemed a bit high. I continued checking the 24V voltages for LED1 through LED8 on the IW7018. Normally, these should be around 1V, but each had different readings ranging from 1.2V to 2.3V. The IW7018EN pin was measured at 2.1V lower than expected. The 5V and 3.3V outputs from pins 10 and 11 were not stable, fluctuating around 2.1V. The VIN supply at pin 12 was normal at 12V. Using an oscilloscope, I checked the SPI signal and saw pulsing. Since IW7018 is known to be fragile, I ordered two replacements. After testing, both worked fine and ran much cooler than before.

One important point to highlight: this machine has a 24V power supply, but the actual measurement came out as 38V. At first, I thought it was a power issue, since such a high voltage would trigger protection mechanisms. However, the 12V voltage remained very stable. After checking the circuit diagram and running a test line, I found that the 24V overvoltage protection regulator ZD952 was missing, which explained why the system was still working despite the high voltage.

Okay, let's install it... oh no! Oh my god, I have to smash it again. This kind of problem is common among many technicians, and there's no way around the messy workbench. The capacitor wasn't fully discharged, and the solder strip got stuck. I was speechless. I took a deep breath and kept repairing. I measured the 5V output and found that the current-limiting resistor RB959 was broken. I tested the power chip and found no short circuits. Replaced the resistor, and finally, 5V came back!

Next, I checked the PFC output and found 300V, but the PFC wasn’t working. Measuring the FAN7930 power supply, I saw 1V flashing, which indicated a possible short. I replaced it with a new one, but the fault remained. Then I checked the VCC-PFC output voltage and found it normal. When measuring RF910, I noticed that the 10-ohm resistor was blown, although it looked intact. I replaced it, and this time, the voltage came out! It’s been running smoothly now. I did a lighting test, and the TV looks great!