A Severe Case Of Surge Voltage Damage In IMPEX LED TV Model GLORIA 32
This TV belonged to an employee working in the grocery shop opposite to my house and was brought to me with the complaint that the mains fuse in their house blew on switching on this TV and it was found dead when checked after restoring power in their house. A clear cut case of power failure. I opened the set after my return from the hospital and keeping it on the Verandah of the car porch, used the blower and brushes to clean up the inside thoroughly.
On checking up after bringing the set to my service table, I noticed that the 3.15A fuse was blown. The switching Mosfet was short. A couple of SMD diodes on the 6 PIN switching IC were also short. A 470uF/16V capacitor in the secondary was found bulged. The switching IC would definitely have gone and therefore, I removed all the components in the primary and made it bare. Replaced the bulgy capacitor and another adjacent to it.
Then used my ring tester in the primary winding and found the ringing was healthy with all LEDs glowing. Then applied power and checked the voltage at the tank capacitor, 47uF/500V. I noticed that the voltage was initially building up to 325, but dropping gradually. As there was no load, this is a wrong sign. I replaced this capacitor and then checked and found that the voltage was steady and it remained like that. Let us have a look at the tiny 6 pin IC and another connected image.
The replacement of the IC was not available and the only option was to provide a 5-24V module or a five wire module. I opted for the 5-24V module because of the recommendations of my techie friends. You will notice from the second picture above, I had removed the oscillation filter circuit from the primary, which consisted of four 104 SMD resistor (100K) and two 10 Ohm resistors, one parallel capacitor, 222K/1KV, and an SMD diode. This was a mistake. This circuit should be there as a protection for the Mosfet and correcting noise. So, I replaced these resistors and the diode later.
The anode of the diode should be connected to the drain of the Mosfet. The two sets of 104 are in parallel, the 10 Ohms were in series. The capacitor had got punctured, so I replaced it with a new one. Then I used a safety trick as suggested by my techie friends: Check that the opto-coupler circuit of the original board is good. If that is ok, cut the pins 3 & 4 in the primary side. Then remove the pin 3 & 4 of the opto in the 5-24 module and remove the blue and yellow wires and directly connect the 3&4 to the TV board. In this way, the secondary voltage will be generated as designed by the TV manufacturer and maintained it that way by the primary of the module. In a way, we can say it is a sort of ‘grafting’, using the best of both. The red wire of the module was connected to the return wire of the SMPS transformer (point where drain was connected), the other end of which is fed the B+. The black wire was soldered to the hot ground.
That’s all! Let us look at some pictures:
I had tried the working before putting the 104/10Ohm resistors and diode in the primary and it was found working. Hence you might see a few pictures without these components in place. I fixed the module on the LED backlight metal back-cover with a heat sink pad provided underneath. The picture you see below is just to show how it was fixed, as I removed the board again to populate the 104/10Ohm resistors and diodes in the primary.
The secondary voltages were 12V and 48V (for the LED driver section). I allowed the TV to run for several hours before putting the back cover and informing the customer to come and pick it up.
I had also replaced the 100uF/63V cap, 22uF/160V and 470uF/10V and that is why you would find these in the tray above. The SMD components that you see at the bottom are good ones, but I did not want to keep it and gave to the customer along with the defective components.
Great mission accomplished for which purpose, I got up at 3 AM in the morning though I had hit the bed only at 11.30PM in the previous night. Intense satisfaction in the verge of bursting got quickly tucked to the collection bag to avoid another damage! (LOL)
P.S: Some of you have been enquiring about this 5-24 Board. Here are a couple of pictures of the cover, which is in Chinese. I used Translator online and got its English version, which are also given:
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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