Change Changhong plasma 3D51A5000i repeated burning PFC power correction (common disease)! ! [board number: LJ44-0023... - appliance repair

Shunluo Inductance Power Inductor SWPA Series First Class Agent

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Changhong 3D51A5000i is another powerful machine that often fails due to no power. I've seen many cases like this. Anyway, I've come across it more than once!

When I tested the power plug resistance, it was infinite, so I suspected the power board was damaged. On-site, I didn’t disassemble it immediately but just checked a sample and concluded that there was an internal circuit failure. The customer agreed to repair, and we took the unit back to the store for further inspection. After opening it up, I found that the PFC had blown, and some of the components were missing or not properly soldered.

Looking at the power tube area, the soldering looked like it was done by a cockroach. Big brother, are you trying to throw it into the grill? Your welding job is terrible, and it hurts my eyes to clean it up for so long.

I noticed that the two power tubes were different models. One was 7N80, which was burned out, while the other, STP14NK50ZFP, was still intact. Even if it wasn’t damaged, replacing them with mismatched components would cause problems later. A wrong replacement could lead to early failure. That’s not something you want to deal with after repairs.

Suddenly, I spotted a small black spot.


No matter how strange the fault might seem, I always manage to catch it. My eyes and nose are quite sensitive—especially my nose. I can detect unusual smells from overheated components. So, when I use a soldering iron, I often smell around and re-solder if needed. I'm particularly sensitive to cracks in circuits and burnt areas. It's almost instinctive for me now. Even on a board I’ve never seen before, I can spot something unusual. It's a bit like being the king of the strongest brain, though I don’t exaggerate it too much. This sensitivity came from an accident over 20 years ago. I was very young when I got injured in my right eye, almost losing my vision. My left eye became increasingly nearsighted over time. By high school, I couldn’t see the blackboard clearly without glasses, and even then, it caused headaches. I avoided eye exams as much as possible, always being the last one to go through them. But I stayed optimistic, laughing it off every time.

Although my vision isn't perfect, it doesn’t interfere with my daily life or work. I just thought I should share a bit of my story here.

Following the same path, I traced the inductance feedback pin and saw that there was high voltage coming in. How could the resistor be burned like that? I also checked the power chip SPC1012T, but it wasn’t tested. I definitely knew it was faulty. Replacing parts blindly can lead to more damage. Don’t skip the most important steps. Whether it's Samsung or Changhong, I've noticed that power inductors often have similar issues. The primary and secondary PFC inductors tend to short-circuit due to poor insulation. When the sampling winding and primary coil heat up, it's easy for them to arc. Many so-called "technical upgrades" are just packaging changes. The materials are the same, and the problem still exists in Samsung machines as well.

The correction inductor was removed, and the feedback winding was burned open.

Then I measured the primary and feedback pins, and they were shorted. If you replace the IC and MOSFETs blindly, the 300V line will keep blowing up the SPC1012T.


The air cylinder was heated gently, and the solder was soft enough to pull out.

Removing the insulating tape was straightforward.

Be sure to check that the other coil isn’t broken and handle the insulation carefully to avoid future issues. The feedback coil was rewound according to the original number. The main coil was cleaned and insulated, so no need to replace it. All connections were made properly and secured with silicone. I replaced the bad 14NK50, cleaned the G-pin pads, and replaced the SP1012T and burnt resistors. Based on comparative analysis, this 20K resistor was definitely faulty. Learning to read circuit diagrams is essential, but I usually don’t look for them unless necessary. That’s why I rarely post schematics.

At the same time, I checked the two 450V capacitors. One of them had shrunk slightly and showed signs of bulging. I used a new one instead of the original. The Panasonic board was too big, but I managed to fit it in. Silicone was used to secure everything.
After checking again, I grounded PS→ON, connected VS→ON to 5V, and powered the unit with a 200W bulb. I also hung a 15W refrigerator bulb as a load. The power was normal, and I put on the insurance. Then I increased the load to 100W and ran the test for 10 minutes. The temperature rise wasn’t significant.


I placed a thermometer inside the case and covered it for an hour to ensure the temperature didn’t exceed 55 degrees.

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After installing the back cover, I tested the machine for a full day.




Even though it was only 100 units, it taught me a lot. Sometimes, learning from 100 mistakes is better than just following instructions. It's all about experience and observation.