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Burst FBT Found In 21” CRT TV With China Kit

By Jestine Yong on November 13, 2018

This TV was brought to me with the complaint that smoke came out when switched on. Though the label shows Sharp 21TK21, it contained China kit, which was fit in a very crude way. The front panel was stuck with tape and was found hanging loose. The input board at the rear was fixed awkwardly, with only one screw. As usual the primary responsibility is to clean the inside of the TV. Just have a look at the inside of this TV, which not only had cob webs, dirt and filth, but also rat excretions!

Now look at the inside after cleaning:

The next job was visual inspection of the Board, which brought out defects such as burst capacitor, burnt resistors and dry solders:

As you will notice, the ABL circuit is the one that had got affected, indicating defects in FBT.

So, I removed the FBT and look at what I found:

The PCB was found charred under the burnt resistors and jumpers under the LOT were also badly damaged, probably due to arcing:

I got the replacement for the FBT and fixed it, cleaned the PCB thoroughly and obtained the values of the burnt resistors from my friends in Technical Support Group and replaced the burst capacitor and these two resistors and also replaced the jumper wires. Replaced the PTC as it was found strained. Retouched the board from one end to another end thoroughly and then the CRT PCB. Cleaned the PCBs very well to remove flux. Lubricated the connectors, including the two insertion type sockets on the CRT PCB, for Focus and Screen Voltages.

Fixed the Front panel with two screws. Connected the board to the CRT : (1) Two connectors that come from the front panel to the board (2) Twin pin of degaussing coil (3) twin pin of Mains Cord (4) Speaker Connectors (5) CRT PCB to the CRT pins (6) Yoke connector to its pins on the board. (7) Horizontal Yoke connector to the pin near the FBT, where it was originally connected. China kits have the facility to adjust the width by selecting appropriate pins provided for 14” to 21”. As this is already explained by me in detail in my earlier article on fitting China Kit in CRT, I am not repeating it here. (8) Anode pin with cap to the anode socket on the CRT (9) Most importantly, soldered the earth wire from the earth connection behind the CRT. (10) The input board. (11) Adjusted the screen and focus voltage on the FBT to the minimum (this is essential when we replace the FBT.)

As I had already tested the power supply of the board by disconnecting the input to the FBT and giving a load of 100W Bulb in its place, I was sure of connecting the board to the CRT and see. Powered on the set, waited for the filament to glow, and then adjusted the screen voltage such that the screen is dark when the brightness, contrast, color and sharpness are at minimum. Then readjusted the brightness and contrast, after feeding a video signal and adjusted the focus for a sharp picture and then adjusted the color and sharpness for a pleasing effect. Allowed the set to run for several hours before ringing up the customer to come and collect.

The first picture you see was taken after completing the work.

For those of you who are interested, following was the uController IC in this kit, which is quite old:

Thus a completely satisfying work got added to my ever growing satisfaction bag!

This article was prepared for you by Parasuraman Subramanian from India. He is 69 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/flyback-arcing-and-burnt-crt-base-pcb-found-in-14-crt-tv/

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Television repair

15 Comments

MR ANTHONY PATERSON

November 13, 2018 at 6:16 pm

Parasuraman you are the consummate professional and your thoroughness is an example to us all HOWEVER in a commercial setting this volume of repair work would be deemed uneconomical.

Your friends with inservicable electronics are very fortunate in having your services.

Thank you for another in-depth article.

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- Robert Calk Jr.
  
  November 13, 2018 at 10:08 pm
  
  Hi Anthony, CRT's are very serviceable. I would repair one, but they seem to be an endangered species here in the USA.
  
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- Parasuraman S
  
  November 14, 2018 at 2:02 pm
  
  You are very correct. My reward is the satisfaction that I get from such work, and the occupation of my body and mind with a lot of interest and enthusiasm focusing only on a positive result. This will keep my brain active and perhaps reduce hospital visits and expenses, which in turn is a good gain!
  
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Albert van Bemmelen

November 13, 2018 at 7:00 pm

Another great CRT TV repair that couldn't have come from anyone else but you Parasuraman! If I ever get stuck while fixing an old CRT TV I wouldn't know of any better engineer to ask for advice than you!

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Robert Calk Jr.

November 13, 2018 at 10:09 pm

Nice work, Parasuraman. Very good photos also!

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- Parasuraman S
  
  November 14, 2018 at 2:11 pm
  
  Yes, we have overcome the poor image problems after a lot of interactions with Jestine Yong, who was very patient to guide me resolve the issue. The issue was not my camera. The camera was good enough. But when I use microsoft document and shrink the images, the original resolution was getting lost and when Jestine Yong enlarges the pictures, it becomes blurry. Anyhow, thanks to him, we have now found out another way of sending without shrinking the pictures, and converting it to pdf. But I sure took a lot of Jestine Yong's time!
  
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  - Robert Calk Jr.
    
    November 15, 2018 at 4:24 am
    
    Mr. Yong is very kind. I don't see how he has the time to do everything. Maybe he can function on a high level with only 3 hours sleep a night like President Trump. I know that my body needs at least 6 hours of sleep.
    
    I transfer my photos to Microsoft Word while I am writing the article and decide on their placement and which ones I want to use. After I have made up my mind which photos I want, I copy/paste them from Word to PowerPoint. After I finish with text boxes and everything, I make sure everything is saved. Then I click on File, and then "save and send", then click "change file type", and then click on "JPEG" which changes the photo to ".jpg" which automatically compresses the photos. Then I change their names and save them to photos.
    
    Then I change the photos in Word with the newly revised and renamed .jpg photos. Then I proofread the article looking for mistakes. Then I send a copy to my son for him to proofread. After I fix any mistakes that we catch, I send the article to Mr. Yong.
    
    There may be easier ways to do it but that's the way that I am used to, and it's works for me.
    
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    - Parasuraman S
      
      November 15, 2018 at 8:48 am
      
      Many thanks! Never knew one would go to this extent for perfection! And a lot of new ways that I could learn from you!
      
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      Reply
      - Robert Calk Jr.
        
        November 16, 2018 at 2:55 am
        
        That is the reason why we are here - to learn from each other. I also use PowerPoint for taking notes, especially when watching a video. I just take screenshots. Then I crop them, which also enlarges the photo. Then we can write our notes directly onto the photos after we move the cropped photos to PowerPoint.
        
        PowerPoint embeds the notes, text boxes, etc.. into the photos, Word does not. It is a lot better than just scribbling notes on paper because you have the notes on a photo. You can then create a folder for them in pictures to put them in.
        
        The default page in PowerPoint shows a place for a title. You need to change that to a blank page. Then when you paste the photo in it, if the photo doesn't fit the PowerPoint window just double-click the corners or hold the left click and fill the window so you can see the photo well, and save it.
        
        Within the next few months I will need a 2T hard drive unless I start deleting older photos. And I hate deleting photos! lol
        
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Henrique J. G. Ulbrich

November 13, 2018 at 10:16 pm

Another excellent article, Parasuraman. Once again, a lot of patience from you. Just a doubt: what does ABL mean?

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- Parasuraman S
  
  November 14, 2018 at 1:56 pm
  
  ABL stands for Automatic BLANK Limiter. That is achieved by a separate winding on the FBT, which controls the frequency generation to be within the limit. For more information, please visit http://www.noahtec.com/flyback-transformer-abl-line.htm
  http://www.electronicrepairguide.com/flyback-transformer-abl-pin.html
  
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beh

November 13, 2018 at 11:15 pm

Thanks for this very useful repair report .

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Hakan

November 17, 2018 at 12:35 am

Hi there is no FBT on Aliexpress;where do you find FBT,I suppose no FBT on Amazon,too...

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- Parasuraman S
  
  November 19, 2018 at 12:36 am
  
  It's easily available in India.
  
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Yogesh Panchal

November 19, 2018 at 8:07 pm

Excellent! sir

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