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12V SMPS Adapter No Voltage Output Repaired

By on December 21, 2020
12V SMPS Adapter No Voltage Output Repaired

power adapter 12 volt repair

Received 12V adaptor stating problem of not working. Done visual inspection of DC PIN, Wire & Plastic body for Burnout /Physical damage everything seems OK.

Checked for DC output for 12V multimeter is not showing any reading. For further inspection I opened the adapter and done visual inspection of the PCB seems OK no physical damage found. Checked continuity of the output DC wire found ok. So concluded the problem in the Circuit only.

Done some Voltage testing up to main capacitor it shows 300V DC that means up to this section circuit is Ok. But not getting any reading toward secondary side. So decide to check the components by cold testing (Using Multimeter in Buzzer Mode to detect open leaky or shorted components in the circuit).

On cold testing near switching Transistor I found open circuit 1MΩ Resister which is connected between Collector and Base of switching transistor MJE 13009 where base bias voltage is derived from the collector voltage.

power adapter circuit board

power adapter circuit board repair

 Replaced New 1MΩ Resister

replace 1 meg resistor

After soldering new resister I kept the circuit on the mains power for testing.

Now Meter Showing Reading of DC 12.4V on DC output Pin.

how to fix power adapter

Finally reassembled the adapter and now it is ready to use.

how to fix and repair power adapter

This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.

P.S- Do you know of any your friends who would benefit from this content that you are reading now? If so, forward this website to your friends or you can invite your friends to subscribe to my newsletter for free in this Link.

Note: You can check his previous repair articles in the link below:

https://jestineyong.com/lenovo-adapter-customer-sent-it-back-to-me/

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22 Comments

  1. Parasuraman S

    December 21, 2020 at 9:40 pm

    A quick fix by a professional! Well done!

    Likes(3)Dislikes(0)
    • Lewis Spedding

      December 22, 2020 at 5:15 am

      Good repair well done they can be tricky

      Likes(0)Dislikes(0)
      • Yogesh Panchal

        December 23, 2020 at 4:11 pm

        Thank you! Lewis Spedding

        Likes(0)Dislikes(0)
    • Yogesh Panchal

      December 23, 2020 at 4:11 pm

      Thank you! sir.

      Likes(0)Dislikes(0)
  2. Albert van Bemmelen

    December 21, 2020 at 10:50 pm

    I am trying to fix a similar power adapter that also uses an almost similar 13005 transistor but one in smd size. That is used on a mini 5V USB charger board that is placed in a EVO Line wall outlet box hidden in a cabinet. I am still waiting on the 6 pin smd controller with smd code 67A. That apparently is a SG6848TZ1 controller also known as green LD7550BBL controller. Hoping to be able to fix it soon which is always a gamble without any service manual or schematics.

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      December 22, 2020 at 1:22 pm

      I found above info on a Russian website but question if that is the right controller info because it looks as if the pin configuration is completeley different to my with 67A smd chipcode marked PWM controller. So 67A is probably a different controller then the mentioned SG6848 one. With those nasty smd codes we never can be sure!

      Likes(1)Dislikes(0)
      • Humberto

        December 22, 2020 at 2:38 pm

        Could you give me the url of that Russian website? I still have many old Soviet semiconductors

        Likes(0)Dislikes(0)
    • Humberto

      December 22, 2020 at 2:36 pm

      This topic about SMD devices is such a trouble, not always you can get the Scematics or Service Manual.

      Likes(0)Dislikes(0)
      • Albert van Bemmelen

        December 25, 2020 at 5:15 am

        I found this info on the 67A sms code for the SOT23-6 PWM controller through Aliexpress that appears to be a MLX02367 chip:
        https://nl.aliexpress.com/item/4001115144255.html
        No luck on a datasheet however.
        And this website was also looking for the 67A code: https://electronics.stackexchange.com/questions/95952/help-identifying-pwm-controller-67a

        Likes(1)Dislikes(0)
      • Albert van Bemmelen

        December 25, 2020 at 5:26 am

        See also this site on the 67A smd code chip:
        https://radioskot.ru/forum/3-12980-1

        Likes(1)Dislikes(0)
      • Albert van Bemmelen

        December 25, 2020 at 5:37 am

        See also this website on the 67A smd code chip that confusingly says that it is a Thyristor chip:
        https://fr.excesschip.com/product/details/MLX02367A.
        I am disturbed if I ordered 50 of the wrong IC's not being PWM controllers and I just asked the seller for a datasheet.

        Likes(1)Dislikes(0)
        • Humberto

          December 26, 2020 at 9:14 am

          Thanks a lot Albert

          Likes(1)Dislikes(1)
          • Albert van Bemmelen

            December 28, 2020 at 8:06 pm

            http://russian-electronics.com/products/transistors/:2t874a

            And it shows many more Russian components too!

            Likes(0)Dislikes(0)
    • Yogesh Panchal

      December 23, 2020 at 4:13 pm

      SMD Parts & their Coding & some time without marking/coding are always Headache.

      Likes(1)Dislikes(0)
  3. Jaikumar Bidkar

    December 22, 2020 at 3:27 am

    Very fast and nice job, thanks for sharing,

    Likes(0)Dislikes(0)
    • Yogesh Panchal

      December 23, 2020 at 4:14 pm

      Your welcome!Jaikumar

      Likes(0)Dislikes(0)
  4. Raj

    December 22, 2020 at 8:27 am

    Great job.. Straight forward. thanks

    Likes(0)Dislikes(0)
    • Yogesh Panchal

      December 23, 2020 at 4:15 pm

      Your Welcome! Raj

      Likes(0)Dislikes(0)
  5. Humberto

    December 22, 2020 at 2:34 pm

    Wow! Polarization of this transistor was failing anyway. Good repair

    Likes(0)Dislikes(0)
    • Yogesh Panchal

      December 23, 2020 at 4:15 pm

      Thanks! Humberto

      Likes(0)Dislikes(0)
  6. Dany Verhamme

    December 23, 2020 at 8:14 pm

    Ik veronderstel dat de 1 Mohm de start-up weerstand is waarna de SMPS via een gelijkgerichte secundaire hulpwikkeling overneemt. Over die startweerstand staat de volle gelijkgerichte en afgevlakte DC van wel 310 V (evt +10%). Dit is wel erg veel, vandaar dat men meestal de spanning verdeeld over 2 weerstanden in serie van bv 470 kohm
    ============================================
    I assume the 1 Mohm is the start-up resistor after which the SMPS takes over via a rectified secondary auxiliary winding. The full rectified and smoothed DC of up to 310 V (possibly + 10%) is placed over this starting resistor. This is a lot, which is why the voltage is usually divided over 2 resistors in series of eg 470 kohm

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  7. Yogesh Panchal

    December 23, 2020 at 10:17 pm

    Absolutely Right & thanks for your input Mr.Dany Verhamme

    Likes(0)Dislikes(0)

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