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Easy Repair With Only One Diode Shorted In LED Monitor

By on February 27, 2016
LED MONITOR POWER BOARD

 

 

 

 

 

 

 

LED MONITOR REPAIRThis e-wis LED Monitor came in for repair with the complaint of no power. The power LED was not lighted even the main ac was connected.

Once the cover was removed I could see the two circuit boards i.e; power and mainboard-see the photo below:
LED MONITOR MAINBOARD

The main fuse was found to be good so I had to perform the on board voltage test to see if the power supply is producing any output voltages or not. The two output voltages that I had tested were 5 volt and 12 volt. There were no output voltage and this confirmed that the power supply indeed have problem.
VOLTAGE TESTING ON BOARD

onboard voltage checking

I removed the power supply and checked on the two output diodes first. Surprisingly the first component (diode) that I had tested was shorted when checked with my digital multimeter.

led monitor power supply

checking diode

This was the diode that was found to be shorted.
shorted diode

I checked further downstream to see if there is any other components found to be faulty but all checked to be good. Even all the secondary filter caps were checked to be good too. I concluded that there was only one output diode shorted and after the replacement of the diode look at the result below:

circuit board working

how to repair led monitor

suranga

This article was prepared for you by Suranga Bandara who owns an Electronics shop in Anuradapura, Sri Lanka.

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Note: You may check out his previous repair article in the below link:

https://www.jestineyong.com/dvd-player-no-disk-error/

 

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15 Comments

  1. Gregor

    February 27, 2016 at 11:09 am

    Nice ... thanks for the article!

    Likes(5)Dislikes(0)
  2. beh

    February 27, 2016 at 11:20 am

    SURANGA : You told in article :The main fuse was found to be good
    but in same board you found a big diode shorted how do you explain why the fuse did not act ? .and thanks, beh

    Likes(4)Dislikes(0)
    • Engr. Greatl

      February 27, 2016 at 2:38 pm

      Beh it is simple, the fuse was found to be OK and so also all the Components in the primary section was ok but if you look closely in the pictures above you will see that the shorted diode is on the secondary power supply which serves as a fast recovery diode,because it was bad it obstructed signals from going to the output stage which leads to no power.

      Likes(5)Dislikes(0)
      • beh

        February 28, 2016 at 7:45 pm

        Engr.Greatl
        thanks for your answer .you mean this fuse is just functioning only for primary section of smps and not for all the psu and secondry am i right?
        beh

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

    February 27, 2016 at 2:49 pm

    Suranga,
    Congratulations! for this fix.

    Likes(3)Dislikes(0)
  4. Ric fernandez

    February 27, 2016 at 3:59 pm

    Thanks for the article hey guys can you help me pinpoint the problem regarding pioneer stereo no power but the hdmi led blinking model vsx-323-k but the stby power for micom are ok.3.3v and 9v any hints guys thanks to all of you.

    Likes(2)Dislikes(0)
    • Parasuraman S

      February 27, 2016 at 11:58 pm

      Pl disconnect power supply to the amplifier board or section. In Pioneer Stereo, most of the times the mosfets that control 25V or similar gets shorted (for STK series amp ICs). So, isolate the power supply to this and check whether the LED is blinking. It is always better to search for free service manual for this model in google and study the circuitry. They might also give clue for the LED blinking in the service manual, under troubleshooting.

      Likes(2)Dislikes(0)
  5. Graham Robinson

    February 27, 2016 at 3:59 pm

    Well done Suranga,i always enjoy reading your articles. Here in the UK we have too much of a throw away mentality when equipment fails which is why there are less & less people like you (and me) capable of repairing down to components. Also it's nice once in a while to get an 'easy' repair in for a change, i hope you made a good profit on this one 🙂

    Regards
    Graham

    Likes(6)Dislikes(0)
  6. Robert Calk

    February 27, 2016 at 7:20 pm

    Good job, Suranga.

    Likes(2)Dislikes(0)
  7. Parasuraman S

    February 27, 2016 at 11:53 pm

    One of the few 'gifts' or 'give aways' we, technicians get in our life! Anyhow, nice to see that the intuition developed out of your involvement and experience helped you catch the 'culprit' soon!

    Likes(3)Dislikes(0)
  8. Akure, Olayinka

    February 28, 2016 at 3:25 am

    Thank u very much, i have been reading all your write -ups and am becoming very good in electronic repair.

    Likes(3)Dislikes(0)
  9. Suranga Electronics Sri Lanka

    February 28, 2016 at 4:35 pm

    Hi my friends and Experts... Thanks so much your Feed back. Thanks All of you!!

    Likes(2)Dislikes(0)
  10. jerry

    February 28, 2016 at 7:41 pm

    Nice one. Thanks.....

    Likes(2)Dislikes(0)
  11. Mark

    March 1, 2016 at 9:48 pm

    Hey Suranga,
    Thanks for the article. The diagnostic path makes sense and by isolating the circuits, the fault can be found.
    Well done!

    Likes(0)Dislikes(0)
  12. Humberto

    March 4, 2016 at 10:52 pm

    Another repair Suranga, congratulations

    Likes(0)Dislikes(0)

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