Shorted MDF11N65B FET and 331, 1kv Capacitor In TV Power Supply Board
An LG LED TV was brought to my shop by a guy who is in charge of maintenance at a hotel nearby my place. He has more than 10 TV’s for repair but he brought only one to see if I can fix it and of course the cost. This set was completely dead.
Since this was a test to see if I am good enough technician to get the TV fixed, I was willing to open it and do my best to get it up and running.
The reason I said that because I really hate LG brands and the parts are too expensive to buy and most of the times, they are hard to find.
Once the cover was off and I was able to see what inside the TV, I started scanning for problem on the power board. The first thing that I checked was the fuse and it was open.
Since the fuse was open, the first thing I checked was the bridge rectifier and it was not shorted. As I was scanning for clear sign on the power board, I came across something that looked dark in the secondary section of the power supply. And I believe something was shorted and even one piece was missing.
This is a closer look of the damaged area. The part shorted was MDF11N65B and if you look closely next to the heat sink you will find what left of the blown capacitor.
The Mosfet is 650 volts and the current 12 amps rating. The capacitor which was blown is 331k, 1kV.
These were the only shorted parts found on that power supply.
I managed to find the shorted Mosfets in my shop because I have some of bad LG power supplies in my shop.
I replaced the shorted parts with used parts from the old powers supplies that I have in my shop. Before I powered up the set, I added a light bulb to the fuse pins to make sure there are no shorted parts left on that power supply (sorry, I do not have a photo of it).
The light did not come on at all and that was my green light to add the fuse to the board.
Mission accomplished.
This article was prepared for you by Waleed Rishmawi, one of our ‘Master Authors’ and currently working in the Bethlehem area of Palestine repairing electrical and electronic equipment.
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Parasuraman S
November 9, 2018 at 12:42 pm
A intriguing explanation of SMPS repair. Enjoyed every bit!
Waleed Rishmawi
November 9, 2018 at 7:14 pm
Parasuraman: I am glad you liked it
Claude
November 9, 2018 at 1:31 pm
Very interesting; Love to see how the root of the problem is detected step by step.
Please keep it up; there could be many like me who await repair articles by Jestine Yong.
Waleed Rishmawi
November 9, 2018 at 7:16 pm
Claude: I am glad you liked it. have a blessed day
doraiswamy SR
November 9, 2018 at 3:05 pm
what may be the reason for shorted MOSFET and burnt capacitor????
Waleed Rishmawi
November 10, 2018 at 5:11 pm
Doraiswamy: well, according to the customer there was a power surge that hit the hotel and shorted out about ten tv sets in that place.
Albert van Bemmelen
November 9, 2018 at 4:13 pm
Thank you Waleed for sharing this interesting LG repair. I am confident that although they are LG's you are fully capable in fixing all other defect hotel tv's too!
Waleed Rishmawi
November 10, 2018 at 5:12 pm
Albert: you are most welcome and I appreciate your confidence in me. have a blessed day
Joshua Oloo
November 9, 2018 at 8:24 pm
Hi,short and precise article with the help of light bulb trick.Thanks
Waleed Rishmawi
November 10, 2018 at 5:13 pm
Joshua: you are most welcome. have a blessed day
A.R.Balasubramanian
November 9, 2018 at 9:17 pm
Useful article
Thanks
However I find hard to repair Printer power supply unit, not showing any signs of physical damage on the components
Model no.k30321
Please let me have suitable guidance
Waleed Rishmawi
November 10, 2018 at 5:18 pm
A.R.Balasubramanian: thanks. well, did you check the fuse? is it open? are you getting voltage reading on the main capacitor? are you getting voltages on the secondary section of the power supply? use common sense. if you do not get any voltages on the main capacitor, you need to go back and find out why? if the fuse was open, that means diodes in the bridge rectifier are shorted..that sort of things. good luck
litec
January 27, 2019 at 7:11 am
dear waleed,
i would like if you can guide\help me please(as im dont know that much on troubleshooting & repairing ) to repair my LG tv from this series line[ mine is 32ln542]
im was home then heared something "POP" then lok to the tv[ which was on standby that time] and saw the red light was gone that moment i realized the psu is failed' disassemble the tv and found that:
the MDF11N65B shorted
one blue 1kv cap near it was cracked
the r113 was burnt too [around the mos]
TH101 thermal res was cracked too
the main fuse was blown[ obviously but probably a bit late]
i do already replace (by another PSU's i have at home:
r113 res.
the 1kv cap
fuse
thermistor[th101]
and mosfet with a new ST 15NM65N[ im dont know if its 100% compatible its an 650v\15a but have some difference between another values
then im plug only the psu without led& main MB to the psu out to minimized problems' and THE FUSE BLOWN
im not that familiar with SMPS but what else can be faulty\ shorting the fuse and how i figured it out?
thanks a LOT!
litec
January 29, 2019 at 10:16 pm
ANY HELP PLEASE FROM SOMEONE??