Dead SONY KLV-40R472A LCD TV Traced To Faulty PFC Adapter And Brought Back To Life
MAKE AND MODEL NO: Sony LCD TV model KLV-40R472A
COMPLAINT REPORTED: Now dead. Sometimes it gets on and sometime it does not.
HISTORY: This TV belonged to a person living a few houses away, in the same street where I live. He is known to me for many years and also is a member of our Residential Association. Since there is containment due to Corona, he knocked at my gate, which was always kept locked, and checked whether he could bring his TV as it was found dead. Due to movement restrictions, TV/Audio Systems/Mobile are the only entertainments available to the residents. So, I told him to bring the Adapter first instead of the TV, as I learnt from him that the TV worked from it. Collected from the gate itself when he brought it, sprayed sanitizer on it and left it at the Car Porch for a few hours before bringing it in. I also cleaned my hands using soap as per protocol prescribed to keep ourselves safe. I was also wearing the mask and maintained distance while receiving the adapter.
TROUBLE SHOOTING, RECTIFICATION AND TESTING DONE: The cover of the adapter is glued together and there are no screws to be opened, perhaps to make it as economical as possible. So, I used my pen knife to make an incision on one corner and pried it open, without causing much damage to the edges. After removing the two half thin metal covers, one side of which is screwed and another soldered to the Earth point of three pin AC input, removed the mica cover to view the inside. There were no bulgy capacitors or burnt components. This is a PFC Adapter; probably because of the higher watt consumption of the TV (it is rated 76W), as per regulations prescribed by the National Grid Authority of India. Applied power and checked the output. It was showing correct output. So, I loaded a 12V/25W Automobile Bulb through a 4 ohm 20W Resistor. The output got dropped, indicating that there was something wrong in the PFC generation. I checked the voltages across the Tank capacitor in the primary, which was 82uF/570SV (SV stands for surge voltage.) It was showing less, i.e., around 360V instead of around 390 to be found, as per experts’ opinions sought. So, I thought there was something wrong in the voltage building circuit. The PFC IC used was SC2005. Downloaded the datasheet, looked for any defective components around the IC and also the voltage builder IC 3S132 (data of which was not available in the web). Could see a few dry solders in the SMD components. So, retouched all the points on the Board. Removed the Tank capacitor, though the ESR was ok. It was showing 91uF instead of 82uF, which is an indication of drying out. As a Gold Capacitor of equivalent value and voltage rating was not available, opted to put 100uF/450V in its place. Replaced the other electrolytic capacitors also. Removed a few of the SMD components as well as the Mosfets for checking. Nothing was found to be defective.
So replaced these back on to the board. Powered up the Adaptor and gave the same load. This time the voltage was steady. But the PFC Voltage was remaining at 360V. So, I gave additional load of 6 nos. of 12V Torch Bulbs of 300mA each and connected my Computer Monitor too. The total load was then around 3.8A, which was more or less same like the TV. The output remained steady, though the voltage built up remaining at 360 only. So, the next option was to ask the customer to bring the TV, connect it and check. The TV was brought, which I allowed the customer to keep it in one corner. I also ensured that he did not touch anything while coming in or going out. I did the sanitizer spraying and allowed it to remain there for a day. Took it up next day. Connected the adaptor and switched on. The TV came on without any problem. I allowed it to run for several hours. Switched on and off many times, both through Remote and Mains Switch. It worked flawlessly, though the PFC Voltage still remained at 360V. Probably, that was how it should be for this Adaptor. So, disconnected and fixed the covers of the Adaptor using tape. Again I allowed it to run for several hours before I called the customer to come and pick it up. Mission accomplished, a lot of new experiences learnt and satisfaction got collected to its bag.
Here Are A Few Pictures:
This article was prepared for you by Parasuraman Subramanian from India. He is 70 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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You may check on his previous repair article below:
https://jestineyong.com/adjustable-shunt-regulator-found-defective-in-lg-fridge-inverter-board/
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Anwar Shiekh
August 21, 2020 at 10:04 pm
When the AC is distorted the PFC voltage can go higher, so replacing a 570V capacitor with 450V is a bit risky
Parasuraman S
August 22, 2020 at 7:49 am
Yes! I do agree with you! There was no other go! Many thanks!
Albert van Bemmelen
August 21, 2020 at 11:27 pm
Congratulations in reaching this 200th anniversary Parasuraman! Many with those countless replaced bad e-caps in them!
Parasuraman S
August 22, 2020 at 7:50 am
Ha! Ha! Many thanks!
Jestine Yong
August 24, 2020 at 5:51 pm
I would like to give a special thanks to Parasuraman for contributing great repair articles. I really admire your hard work and dedication to this repair field. You are awesome! I also want to thanks those who have contributed and still contributing the articles to make this blog a website that is a must to visit for all electronics repairers. All of you just amazing!
Best Regards
Jestine Yong
Yogesh Panchal
August 21, 2020 at 11:48 pm
Congratulations!for double century.......Sir,
Keep us encouraging by sharing your experience.
Parasuraman S
August 22, 2020 at 4:40 pm
Many thanks!
Henrique J. G. Ulbrich
August 22, 2020 at 12:56 am
Congratulations on these 200 maintenance articles. Indeed, it is an extraordinary achievement. For me, such a feat is impossible, as I don´t deal directly with repair service. Just an occasional repairer, when some of my gadgets (or from relatives/friends) need attention. Anyhow, the time spent in my small workshop is always fulfilling.
A doubt about the voltage on the tank capacitor. You have mentioned voltage levels of 390 and 360 Vdc. As far as I know, the voltage on this capacitor is the line voltage multiplied by 1.414 (square root of 2). In this way, with 110 Vac at line input this voltage is nearly 155 Vdc; with 127 Vac (that´s the case in my city in Brazil) is 180 Vdc. With 220 Vac applied the voltage must be about 311 Vdc and with 240 Vac 339 Vdc. I´d not heard about other voltages, perhaps the PFC system makes the difference.
Joseph Chemai
August 22, 2020 at 11:01 am
It is practically possible... Remember 220vac is an average actual voltage in kenya is 238Vac - 242Vac hence 1.44×238Vac is almost 360Vdc in Kenya... Not sure of india
Parasuraman S
August 23, 2020 at 6:07 am
Yes, you are right. In India, it is 220V to 230V AC 50Hz.
Parasuraman S
August 22, 2020 at 4:45 pm
Yes. PFC circuit builds voltages by pumping into the capacitor, for which feedback is obtained, to keep it steady. That's what provides stability.
Henrique J. G. Ulbrich
August 25, 2020 at 6:26 am
Thanks, Parasuraman. I didn't have enough knowledge of PFC circuits until now. This motivated me today to look for information in Internet. Now I know that the key is the use of a boost circuit inherent to the PFC circuit, which explains the extra voltage. New for me. Life is an eternal learning. Thanks again.
Parasuraman S
August 23, 2020 at 7:02 pm
Now, when I come to think of it, I select for writing an article, only such cases, where there is something to learn. That is why it is only 200 out of thousands of cases I have handled so far. I always love to aim at beginners, who might struggle to get a grip, after thrown open from a training institute. I mean, raw hands. So, I take care to include basis steps too in many of my articles. I think and believe that imparting knowledge, training and bringing such technicians up is bestowed in our hands, being a fellow living being just like any of us. If we turn back, see and evaluate, we will get many such situations and guiding the upcoming technicians is indeed incumbent on us! Is it not?
Imoudu Onwumah
August 22, 2020 at 2:37 am
How I wish I could get all those past articles to read. I started reading ur articles two years ago and I did enjoy every bit of it.You are a blessing to us
Parasuraman S
August 22, 2020 at 4:48 pm
Many thanks. Just click on the previous article link, one by one. You can read all!
Anwar Shiekh
August 22, 2020 at 6:27 am
Found the document that claims AC distortion can cause elevated voltage on the bulk capacitor
https://digilander.libero.it/hibone/UPS/PSU_and_UPS_Compatibility_Test_Report.pdf
Parasuraman S
August 22, 2020 at 4:48 pm
Many thanks! Shall check!
Parasuraman S
August 23, 2020 at 6:55 pm
I checked the link and also consulted an expert in the field, who is my friend. According to him, the link talks about PFC provided in the UPS. This adapter in the article is a one, which uses a PFC control because of the wattage rating of the TV. There are two types of PFC, one is active and another is passive. This Sony adapter uses active. But passive control as used in UPS and such large devices, is sturdy and more reliable.
Humberto
August 27, 2020 at 1:36 pm
Good repair and Congratulations for your number 200. Have a lovely day.
ivan
September 3, 2020 at 2:39 pm
thanks sir, and congs upon your 200th article
Anne
July 14, 2021 at 7:47 pm
Where can I get the motherboard for the same model number?I am in Kenya and I can't find any.