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Bulged Caps And Bad SMD PWM Found In Two Dead LG 12v Adapters

By on February 9, 2021
Bulged Caps And Bad SMD PWM Found In Two Dead LG 12v Adapters








how to repair power supply adapter

These two AC Adapters belong to the hospital where I work. (By the way, I have resumed my visits every alternative day, after doing online support from house for the past few months!) Both were reported to be dead. On opening Sl. No. 036208, I could see a bulgy 6.8mfd/400V Cap, parallel to which was another 3.3mfd/400V. I removed both and fixed a 10mfd/450V cap in its place.

As this ACA had undergone replacement of other electrolytic caps and retouching solder joints about a few months back, switched on and found it to be working fine. (pictures above). Refixed the cover and checked again:

how to repair power supply adaptor

Opened the other and did not find any bulgy caps. The fuse was intact. ESR of one 10mfd/50V cap in the primary section showed ESR as 27 and value as 3.3. So, replaced it. Checked all other components and also did the ring testing. No defects were found.

blue esr meter check power adapter

Applied power and did not get any output. Checked the VCC of the six pin SMD PWM marked as AAHBM and found it to be dropping indicating a possible failure.

aahbm ic

So removed the Mosfet and connected a three wire universal SMPS module in its place and applied power. I got 12V, indicating that high voltage section primary and outputs were functioning well. (Those of you who do not know about this universal module can see this link : )

smps transformer live tester

So, the next possibility is a defect in the SMPS transformer or connected components in the primary run DC section. In order to check that, I connected a five wire universal module. (I think Jestine Yong has published a book on use of this module) This module uses STR DMO0565. Kindly see following link for datasheet: DM0565 pdf, DM0565 description, DM0565 datasheets, DM0565 view ::: ALLDATASHEET ::: This module has Yellow (Drain), Black (ground), Red (VCC), White (Feedback from Optocoupler), and Green (B+) .

I connected the wires in its proper place and switched on and got 12V, indicating that the SMD PWM indeed was the culprit. As a replacement was not available, drilled holes on the PCB and wired the module from the top. Retouched all the solder joints.

how to fix power adaptor

Housed the module after wrapping it with tape. Checked and found it to be working very well, when I connected an Induction Cooker 12V Fan as load.

(As this is used for Attendance Register device, the power consumption might not be high requiring a heat zinc to be provided for the STR.)

fixing power adaptors

Fixed the cover. Missions accomplished and double satisfaction jumped into the bag happily!

This article was prepared for you by Parasuraman Subramanian from India. He is 71 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:




  1. Waleed Rishmawi

    February 9, 2021 at 4:13 pm

    I have not used this five wire universal module before and I hope they will not generate a lot of heat..thanks for sharing. have a blessed day

    • Parasuraman S

      February 9, 2021 at 8:43 pm

      Many thanks!

  2. Albert van Bemmelen

    February 9, 2021 at 8:23 pm

    Thanks for sharing how to successfully use the 5 wire universal module. I have several of those but was not yet able to make good use of them in any repair. Mainly because most of the defect smps units had defect HF pwm transformers in which the module would not work anyway. And I believe you already said that the 3 wire universal module you used in this and older articles no longer was available?

    • Parasuraman S

      February 10, 2021 at 2:27 pm

      The three wire universal module is still available here. But it is better to use the five wire for power control and reliability. Many thanks for your comments!

      • A van Bemmelen

        February 11, 2021 at 4:27 am

        I searched for the 3 wire universal module Parasuraman but Aliexpress didn't give anything. Do you still have a working link to a seller of those? Could be usefull as a test substitute in case original HF smps tranformers are defect and the electronic controller needs to be tested too. Thanks!

      • Albert van Bemmelen

        February 11, 2021 at 9:58 pm

        I found the link for the 3 wire universal module. This must be the one you mentioned with all info on the site of the seller.

        • Parasuraman S

          February 14, 2021 at 6:43 pm

          Many thanks!

  3. Anwar Shiekh

    February 9, 2021 at 10:28 pm

    I believe that leaving out the smaller capacitor may be an error as the smaller capacitor has less inductance and so can better deal with higher frequencies; it is a common trick to have a small capacitor in parallel with a larger one for this very reason.

    • Parasuraman S

      February 10, 2021 at 2:32 pm

      Yes, you are right. But in this case, fitting two larger size capacitors was not possible. So, I opted for it. Many thanks for your observation and comments!


    February 10, 2021 at 11:40 am

    Hello, can you show the sustitution way of the repair, I didn't find the DM0565 data sheet,please explain with more detail, thanks; is this a safe adapter repair?

    • Parasuraman S

      February 10, 2021 at 2:33 pm

      The link of the datasheet is already given in the article. It is a safe adapter repair! No doubt! Many thanks for your observation and comments!

  5. Imoudu Onwumah

    February 10, 2021 at 3:31 pm

    You said you fìrst use 3wires module and got 12 volt,why then using 5wires module again.i don't understand.

    • Anil Varma

      February 11, 2021 at 2:24 am

      3 wire Module is bigger in size compared to 5 wire Module. Hence 3 wire Module can’t fit inside the AC adapter so, Parasuraman Sir, used 5 wire Module which is small in size.
      5 wire Module is in very compact design, it contains all required components inside its silicon die, thus reduces component count, while retaining high efficiency.
      I hope it helps to your Understanding.

      • Parasuraman S

        February 12, 2021 at 12:10 am

        Yes, that is it. I have overlooked to mention this valid point, though from the pictures, it is very clear!

  6. Imoudu Onwumah

    February 10, 2021 at 4:09 pm

    Is it possible to give the link of the acticle you fìrst wrote how to use smps power module?

    • Parasuraman S

      February 12, 2021 at 12:09 am

      It is already given in the article, dear! Please read fully!

  7. Yogesh Panchal

    February 12, 2021 at 3:03 pm

    Good fix......
    Now a days most of SMPS are difficult to repair because of those 6 pin PWM IC you have mentioned because of unavailability in local market.using external module also good idea but some time it does not feasible because of space restriction.

    • Parasuraman S

      February 14, 2021 at 12:55 am

      Yes, very true! Many thanks!

  8. Lynn Blakely

    February 13, 2021 at 12:07 am

    Good Job to Parasuraman. We enjoyed all to comments and conversation. Very educational. Thanks to all that contributed.

    • Parasuraman S

      February 14, 2021 at 12:56 am

      Yes, very true! Many thanks are due to everyone's dear Jestine Yong!

  9. Humberto

    February 15, 2021 at 8:16 am

    How much in your collection bag? Is it full? You will have to buy another one. Lol. Thanks for sharing this article.

    • Parasuraman S

      February 15, 2021 at 5:44 pm

      Ha!Ha! Many thanks! Shall try to borrow one from Santa Clause!


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