No Picture Problem Solved In Blueberry’s 32” LED TV Model BRN-32
This TV was brought to me by a regular customer with the complaint that there was no picture, but sound was ok. I opened and cleaned the set and looked for any bulgy capacitors or any noticeable defective components and then checked the voltages and found these to be ok. The 12V was reaching the scaler board, but the AVDD and VGL/VGH voltages were missing. The scaler board was using SM4186 IC. I looked for the schematic and got one from the web. I traced the VCC pin and found it to be present.
The 3.3V and 1.8V was also present. So, the IC was going to protection mode due to some shorting in the panel. On seeking help from techie friends for tracing the CKV lines on the scaler board, I got it correctly marked, which I am sharing below:
The last picture above shows the CKV llines. The fist pin is linked to third pin. The second is linked to the fourth pin. I checked the ohms between 1st and third and found it to be 300 Ohms indicating a short. It should only be Meg Ohms.
These CKV lines are interconnected and goes from both sides of the COF into the panel; i.e., there are pairs of these lines at both left and right side of the COFs. So this short could either be on the left side of the Panel or Right side of the panel. If we had a T-con board instead of the scaler board with two separate COFs, we could have easily removed one & checked. But that was not possible here. The only way was to check the continuity at one end and try our luck by cutting one line to check whether the short has gone.
If not, we need to cut the same track on the other side and if the short has gone, rejoin the first one, which is a very intricate job and we need to use a microscope or X10 lens with a very tiny tipped soldering iron. For cutting we need to use surgical blades and cut the tracks slantingly for an easy rejoin if needed. For my luck, the problem was in the left side (when viewed from keeping the TV face down) and the short got removed when I cut the first track. The picture came back then when powered:
Then I cut all the six tracks on that side taking due care, which can be seen in the following picture:
Why did I do that? From the experience of techie friends, they advised me to do that as they have seen short developing to the adjacent tracks soon and complaints repeating. Though they asked me to short all the six pins on the panel side, I could not manage that as the lines were too tiny to hold solder or a thin hair like wire.
But the TV worked very well for hours together and according to my friends, it would work very well without this shorting. The shorting was being done to prevent a possible carbon deposit short. But many techies did not do that and the TV worked for months together without any problem.
Mission accomplished with satisfaction getting added as accustomed.
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
January 25, 2025 at 12:51 pm
That is new information add to my knowledge, thanks I am glad it worked out without going through too much hassle. Have a blessed day
Parasuraman S
January 25, 2025 at 6:41 pm
Many thanks, dear friend!
Mark
January 25, 2025 at 12:57 pm
Well done Parasuraman,
Excellent diagnosis!
Parasuraman S
January 25, 2025 at 6:41 pm
Many thanks, dear Mark!
Yogesh Panchal
January 25, 2025 at 2:40 pm
Good Job! Sir
Seen peoples use Short Killer for removing short but this is the safe way.
Parasuraman S
January 25, 2025 at 6:42 pm
Short killer has too many risks involved and it is not lasting for a desired time. Many thanks, dear Yogesh Bai!
Tayo
January 25, 2025 at 11:56 pm
The short killer method which I found on YouTube looks like it can kill the whole device.
And if the short is in the panel what happens?
Albert van Bemmelen
January 25, 2025 at 3:19 pm
After reading this again incredibly smart carried out lcd tv repair, it sadly only feeds my doubt on taking on such difficult repairs especially without having any experienced techie friends around!
Parasuraman S
January 25, 2025 at 6:43 pm
Go to some scrap yard, pick up a couple of these types of TVs, do all these experiments and acquire knowledge. That's the only way! (LOL) Many thanks, dear Albert!
corriette
January 25, 2025 at 5:32 pm
wow! excellent . very much thank you for sharing. Experience, knowledge...WISDOM
Parasuraman S
January 25, 2025 at 10:47 pm
Many thanks!
Tayo
January 25, 2025 at 11:56 pm
Amazing repair Maestro.
This is the one TV repair that scares me the most.
Cutting tracks and trying to repair them without the aid of magnification....
Mark J
January 26, 2025 at 3:55 am
Parasuraman good job on the repair. You have good diagnosis and repair, skills.I hope to be as good of technician as you are someday.