Sharp LCD TV No Power

By on November 22, 2016
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This sharp lcd tv model: LC32A33M was tested to be dead and unable to power up neither with a remote or “power on” button . When the back cover was removed it was quite obvious of the fault. This TV has been struck by lightning or power surge with black flashover marks on the power supply board (RUNTKA419WJN1) around the Varistor ( photo 1).

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Photo 1- Burnt marks due to power surge

The two fuses were tested and found to be  blown. The function of the  Varistor VA7103  was to reduce the excessive current due to voltage surge.  The excessive current caused it to overheating or overload and breakdown. The resistance measured on the terminals is only a few hundred ohms. The Varistor was temporary removed and a 100w bulb were connected across the blown fuse. When the power was turned on the bulb lights up at continuous full brightness indicating there were still short circuit on the power supply.




I checked on the smps power IC 7101 VSS(pin4) and found to be short circuited to ground .The IC and Varistor were replaced and retested again. The bulb lighted up brightly initially and slowing started to dim indicating there were no more short circuit, but the tv was still dead with no standby power or output voltages on the secondary. Couldn’t find any shorted components on the secondary or primary side of the smps.

It is much easier  to diagnose and repair with a schematic. I could not find the schematic for RUNTKA419WJN1 but by coincidence I found another model power supply (RUNTKA396WJQZ) with the exact footprint and components layout on the board. The only difference is the smps power IC 7101 marked as TNY276PN instead of TNY274PN. Checked with the datasheet showed that it is from the same family but with different power rating (Photo 2)

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Photo 2- power supply schematic for RUNTKA396WJQZ

Pin 4 voltage was found to be normal i.e 340Vdc and the smps should work unless it is in shutdown mode. I observed that pin 2 was designed to monitor the output voltages and any abnormally or high voltages will result in the shutdown mode as stated in the IC  data sheet. I checked all the components connected to pin 2 and found C7124 to be defective or very low capacitance.

After changing the capacitor, the smps turn on with the standby voltage of 5.1v  as shown in photo 3. The TV can now turn on as normal with the remote control or the TV side panel power button.

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Photo 3-standby voltage of 5.1v

skwong

This article was prepared for you by SK Wong from Malaysia and he graduated from London with a degree in Electronics and Electrical Engineering. He has more than 40 years of experience in the consumer product manufacturing. With the passion to repair electronic products from young , he has been doing it part time until now.

Currently, he can provide turnkey solutions for consumer products including services from idea or concept to design , prototyping , finished products (including electronic,mechanical and plastic parts) and manufacturing.




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Note: You can check his previous repair articles below:

http://jestineyong.com/panasonic-microwave-oven-not-heating-hv-diode-faulty/

 

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22 Comments

  1. Ulises Aguilar Pazzani

    November 22, 2016 at 8:09 am

    Mr Wong great job

    Likes(1)Dislikes(0)
  2. PARASURAMAN

    November 22, 2016 at 9:43 am

    Great! Servicing SMPS boards is always a challenge, especially with multiple failures! Informative!

    Likes(1)Dislikes(0)
  3. Robert Calk

    November 22, 2016 at 11:36 am

    Nice work, Mr. Wong. Thanks for sharing the repair with us.

    Likes(1)Dislikes(0)
  4. Albert van Bemmelen

    November 22, 2016 at 3:11 pm

    Thank you for the well presented SMPS repair, Mr.SK Wong.
    Boards struck by Lightning always mean bad trouble.
    But I'm sure you didn't really needed the schematic, cause it did not help you much anyhow being different schematics. And by testing everything on a component-level, you did find the bad parts. You no doubt would have found the Culprit, being a Pro in this field of repair.
    And in case no schematics were to be found, I'm sure examining the datasheet of the TNY274PN would have given you enough information too.

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    • Henrique Jorge Guimarães Ulbrich

      November 22, 2016 at 8:53 pm

      It's correct, Albert. Many times I succeeded in maintenance works by just seeking to the IC datasheet. Not only for knowing the IC functionning itself, but also by the application notes. The same was probably done by the developers of the equipments, so there is a high possibility of the real circuit on the gadget be the same. It helps a lot the maintenance work.

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    • skwong

      November 22, 2016 at 10:22 pm

      I find it much faster to trouble shoot with schematic. Examining the datasheet definitely will be helpful but sometime it is tedious and time consuming. I

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      • Henrique Jorge Guimarães Ulbrich

        November 23, 2016 at 4:36 am

        Agree, skwong. But using the data sheet is the available resource when the schematic is not at hand.

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  5. Samsudeen

    November 22, 2016 at 3:21 pm

    Thanks to sharing the technical details.its able to improve my knowledge.thanks

    Likes(2)Dislikes(0)
  6. Yogesh Panchal

    November 22, 2016 at 3:48 pm

    Good Repair! Sir.

    Likes(1)Dislikes(0)
  7. Noel Gervais Gerard Louis

    November 22, 2016 at 6:11 pm

    Thanks for sharing this articles, I appreciate a lot.

    Likes(1)Dislikes(0)
  8. Andrew F. Ali

    November 22, 2016 at 7:02 pm

    Very good information, Mr Wong...Thank you for sharing..

    Likes(0)Dislikes(0)
  9. suranga Electronics

    November 22, 2016 at 7:57 pm

    Mr-SK Wong.

    Good Repair Article.
    Thanks For This.

    Likes(0)Dislikes(0)
  10. Lad

    November 23, 2016 at 1:37 am

    Thank you for sharing.

    Likes(1)Dislikes(0)
  11. Mark

    November 23, 2016 at 5:38 am

    Lightning does some serious damage at times, but you did well to trace the fault to those components.
    Well Done!

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  12. Paris Azis

    November 23, 2016 at 2:08 pm

    Nice work, Mr Wong. Fortunately thiazide appliance had a varistor included. It could have been much worse than that failure.
    Thanks for sharing it.

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  13. Bulent NUR

    November 24, 2016 at 12:30 am

    Thanks for sharing very informatively!

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  14. Silveter un

    November 24, 2016 at 8:20 pm

    very good.Ihave politron 32 inchi problem bluelight.sound its oke.help me

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  15. Ulises Aguilar Pazzani

    November 27, 2016 at 12:12 pm

    Mr Wong , great repair keep it up

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  16. Humberto

    November 28, 2016 at 11:46 pm

    Good repair. Thanks for sharing this article.

    Likes(0)Dislikes(0)
  17. sửa điện nước

    December 3, 2016 at 12:17 am

    Thank you for sharing

    Likes(1)Dislikes(0)
    • Ruben

      December 9, 2016 at 11:36 pm

      hi! sir , it 's marvelous , i APPRECIATE WELL, THANKS TO YOUR ARTICLE, MAY YOU HAVE MORE REPORT TO COME. W/ SINCERITY rUBEN

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  18. Ganthan

    March 6, 2017 at 11:45 am

    Really helpful..

    Likes(0)Dislikes(0)

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