LD7575PS Power IC Shorted
A police woman brought this to my shop for repair. It was a dead LCD computer monitor and it was kept in the storage room for a very long time. This LCD computer monitor was used as a monitor for security cameras. Today this woman decided to get it fixed in order to use it in her own home.
These kinds of LCD models are very easy and cheap to fix.
That is why the moment I opened the back cover, I saw this and I smiled because I thought it was any easy fix. To my surprise, well, take a look.
A bulged capacitor usually is the cause for a dead LCD monitors but I got really shocked to see the rest of the damage.
The main capacitor was also bulged and damaged but still, there was more.
The fuse was blown as well which means either the bridge rectifier is shorted or the Mosfet but in my case, both were shorted. The fuse resister was also damaged as you can see in the photo.
With all the damage, I had to call the customer and tell her the situation. There is always a chance that even with the replacement of all these damaged part, the screen will not work. As a technician I think like that; what if? The customer gave me the green light to get started. I replaced all the damaged part and guess what? It did not work.
I replaced the fuse as well but it is not in the photos. I was right about this screen not working even when all the damaged parts replaced. I did not give up and kept going. Sometimes we get frustrated with this kind of repair because in our mind, all these damaged replaced, took me time and money and yet, nothing works.
The part number of the Mosfet is P9NK70FP which is 700 volts, 1.2 ohm, 7.2 amp and 35 watts. The bridged rectifier number is KBP206G. The rest of the parts are very clear in the photo.
At this time, the short was gone and I could power it on and start to check the voltages there. The power was reaching the main capacitor and it was steady but that all it was. I unplugged the LCD screen from the main power and started to check for bad components.
There was a capacitor nearby this IC location and it was reading short on it. I traced back the line to this IC. The part number is LD7575PS. I added flux on it and with a re work station I de-soldered it off board.
The moment, the IC was off, the short on that capacitor was gone. The only way to find such replacement was to take it off another power board from another LCD monitor. I was lucky to find one on a Proview 900W model. Ones I replaced it, I got this.
The standby came on and then I saw this on the screen.
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
June 7, 2018 at 11:18 pm
Very useful and informative tips! Great job! Many thanks for sharing!
Waleed Rishmawi
June 8, 2018 at 5:50 pm
Parasuraman: you are most welcome
Jonathan
June 7, 2018 at 11:46 pm
The backlights on the monitor are old the text is pink instead of being white. So looks like the lamps will have to be replaced soon too.
Waleed Rishmawi
June 8, 2018 at 5:51 pm
Jonathan: yes you are right. I have seen that. I offered the customer to change the back light or the whole panel but she refused.
Mihai
June 8, 2018 at 12:48 am
Hello, Good job sir !
Waleed Rishmawi
June 8, 2018 at 5:52 pm
Mihai: you are most welcome.
vikrant warange
June 8, 2018 at 4:21 am
Good Job...
Waleed Rishmawi
June 8, 2018 at 5:52 pm
vikrant: thanks. have a good day
Muiddeen
June 8, 2018 at 6:24 am
great job and interesting
Thank you sir.
Waleed Rishmawi
June 8, 2018 at 5:53 pm
Muiddeen: you are most welcome
Albert
June 8, 2018 at 9:25 am
Well done! Getting the replacement parts delivered fast enough is always a problem. Good thing you found a spare one.
Waleed Rishmawi
June 8, 2018 at 5:54 pm
Albert: yes indeed. many times, i find what was wrong but lack of parts make it hard to finish the repair. that is why I keep boards of LCD and lED screens in my junk box. it is worth it.
Robert Calk Jr.
June 8, 2018 at 11:05 pm
Good job, Waleed. Thanks for sharing the repair with us.
P.kumaresan
June 9, 2018 at 12:44 am
Thank you sir
Ronald
June 9, 2018 at 6:46 pm
Hi Waleed, nice article. I wanted to ask you to clarify what you meant with
"There was a capacitor nearby this IC location and it was reading short on it"
Can you explain how you go about checking for shorts on these SMD capacitors?
I allways check with the - on the cold or hot ground and the + on both side of the SMD caps and check if if short on both sides instead of only one side, what you expect.
Waleed Rishmawi
June 13, 2018 at 4:28 pm
Ronald: thanks.
there was a capacitor on the same line of this ic. since the IC was shorted, when I tested this capacitor, the tester showed me a short but the moment I de soldered the ic, the capacitor not reading short any more.
I have a SMD tester that looks like tweezers and so far, it worked fine with me.
Tyronet
June 10, 2018 at 3:24 am
Very good repair Waleed thanks for sharing.
Waleed Rishmawi
June 13, 2018 at 4:28 pm
Tyronet: you are most welcome
Yogesh Panchal
June 12, 2018 at 1:08 am
well done! waleed.
Yogesh Panchal
June 13, 2018 at 12:28 am
Good Job! waleed
Waleed Rishmawi
June 13, 2018 at 4:29 pm
Yogesh: thanks and blessings to you
Alexan Catalin
June 26, 2018 at 8:08 pm
Hello friends !
I want to thanks to Jestine Yong, for this nice site and discussion forum.
I want to salute my neighbor Christian Robert Adzic from Novi Knezevac-Serbia. I am from Timisoara-Romania.
I'm following all the articles !
Thank you to all, my friends ! God bless !
Alexan Catalin