Dry Solder Caused Lead Of EMI Filter Coil Getting Charred In LG DVD Player Model DV692
This DVD was brought by a recently added regular customer with the complaint that it was dead. I opened it and cleaned the inside as usual. Checked whether the problem was in the AC input. AC input was present. But DC was absent in the primary switching section.
I removed the board and did a visual examination and this is what I found:
There was a lot of dry solder on the PS Board and one leg of the EMI filter coil was found charred. I removed this coil and studied the extent of damage. There was only a tip protruding at the bottom, which was unfortunately from the inside winding. Nevertheless, having aroused my enthusiasm to do what is impossible; I cleaned that tip, applied a bit of flux and placed a tiny ball of solder on it. Then cleaned the remaining portion of the leg and did the same on that too.
Then took a very thin wire and soldered and joined both. Let us have a look:
Then carefully added a long cut lead on that leg for enabling solder on the PCB. Then fixed it and did a thorough retouching of the board from one end to the other. The capacitors were found healthy. The voltages of 12V and 5V were present when I applied power keeping it externally.
Lubricated all the connectors and fixed the board back in its place, connected it to the mother board. The DVD got on and played very well. But the tray in and out was sluggish. So, changed its belt. This was one of the quickest services done, bringing satisfaction for addition:
This article was prepared for you by Parasuraman Subramanian from India. He is 74 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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Waleed Rishmawi
May 24, 2025 at 1:32 pm
very good repair my friend. re touching that faulty coil was a good idea and I am glad it worked out fine. thanks for sharing and have a wonderful day
Parasuraman S
May 24, 2025 at 7:35 pm
Many thanks for your comments and encouragement, dear friend!
Yogesh Panchal
May 24, 2025 at 3:52 pm
Good Job!Sir
Many cheap Manufacturers using Metal wires instead of copper wire in electronics parts like transistors /resistors /LED & more which cause rust over period of the time & degrade equipment early.Government should have some guideline for this types of manufacturers.
Parasuraman S
May 24, 2025 at 7:37 pm
I do agree. Let the government also fix some rules and regulations for the MRP marked on the boxes! Those are almost double or treble in many cases! Many thanks for your involved comments, dear Yogesh Bai!
Albert van Bemmelen
May 24, 2025 at 6:46 pm
Getting a new exact matching core with coil probably would be a major problem in this case. So repairing the original coil was no doubt the best option here!
Parasuraman S
May 24, 2025 at 7:38 pm
Yes, that's true! Many thanks, dear Albert!
Humberto
May 24, 2025 at 8:39 pm
Of course Albert, that original coíl
is very well calculated in the design for the Engineer
Parasuraman S
May 24, 2025 at 11:53 pm
Yes, true!
Humberto
May 24, 2025 at 8:40 pm
Another electronic device saved from the dump
Parasuraman S
May 24, 2025 at 11:54 pm
Yes, dear Humberto and thanks!
Mark J
May 25, 2025 at 2:40 am
Parasuraman thank you for sharing your knowledge and experience. Good job on the repair.
Parasuraman S
May 25, 2025 at 10:24 am
Many thanks for your encouraging comments, dear Mark!
Mark J
May 26, 2025 at 3:14 am
You are welcome. I am still aspiring to be as good of a repair technician as you.
Imoudu
May 25, 2025 at 11:57 pm
Such filter coil is hard to buy except you get replacement from scrap,but you manage to mend it,good job sir.
Parasuraman S
May 26, 2025 at 2:05 pm
Many thanks, dear Imoudu!
Muykit
May 26, 2025 at 6:57 am
Thanks Engineer Parasuraman. Luckily. the EMI coil survived being 'shorted', though they rarely get destroyed anyway, especially the twin-coil ones that are often connected in parallel. I guess the rectifier diodes, a ceramic capacitor, to some extend the main input capacitor, and probably the main fuse too, were spared because the EMI coil never got burned (shorted) while remaining properly connected to the power cicuit board. In my minds eye, the coil hard a poor connection or dry joint in the power circuit that created a restance high enough to minimize current flow that would have otherwise caused extensive damage to the power input components including but not limited to the power fuse. 2. I often wonder why small smps circuits, for example those of TV external adapters or TV set top boxes have no EMI coils in their input power supply yet they work just well enough without much harm with only the rectifier diodes taking care of unecessary reverse current flow ?
Parasuraman S
May 26, 2025 at 2:09 pm
Thanks for your elaborate and valuable comments, dear Muykit! The primary circuit depends upon the expected load and if these are minimal, the EMI circuits are excluded. But there would be adequate compensation in the main board for sure, because noise is an important factor in power supply circuits.