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Another Adapter Repaired 4.2V 0.5A And Tested Using Supertip

By on January 22, 2021
supertip repair small power supply

This small adapter repair was put aside for quite some time after I already had repaired all obvious defects and had also fixed a burned through copper track. And because the 4.2V 0.5A adapter board still refused to start working after all the destroyed parts were replaced I once and a while picked it up to examine the small adapter board again. And why this adapter short circuited and blew away a primary copper track in the process was unknown.

Until I recently on one of those days finally found why it still wouldn’t work! Of course I also had drawn a schematic by examining the board layout. Here it is, followed by the fixed solder board side:

small power adapter diagram

how to fix small power supply

It had no active PWM controller, only 2 primary transistors. One 8050 and one 13001 transistor , plus the standard optocoupler a 4 pins PC817C. Plus 3 resistors and a primary 400V 2.2uF e-cap and a single 10nF primary capacitor. Below the component side also after the defects were fixed.

how to repair small power supplies

Sad thing is probably that I do not know what this HD-33A adapter was made for because of the secondary connected DUO-LED, I guess it was for some kind of charger. But I am afraid that I already have used the original housing it came in for other purposes. So of that black plastic 230V AC case I now only have a few photos left. Below photos show the original 230V AC housing.

how to fix and repair small power supplies

It turned out that not only the primary components on next photo needed replacements but also the secondary 3.0V zener and the 220uF were defect!

optocoupler ic tester

On above photo my little but great working universal digital tester that disapproved the PC817C optocoupler. You can just see the scrolling ‘r’ of the “error” report. This tester also tests Opamps, TTL/CMOS ICs and even a few other analogue amplifier ICs. And operates on a single AAA cell! This little portable affordable tester never disappoints, and it is incredible how they could design it so tiny with all its functionality!

dy294 test power supply

I afterwards also found 2 left cold solder joints that only showed up when I juggled with the legs of the Duo-Led connected to the bigger 2.2 Ohm (1 or 2 Watt) resistor on the + output track, and the cracked track to the single 230V AC input rectifier diode.

All that time it was just the secondary 220uF 10V e-cap in above photo that still was the culprit because before it was replaced there was no output on the secondary side and only the DUO-LED lit op in green. The secondary 220uF e-cap only had a low pF value left which was totally unexpected.

After I had also replaced this little 220uF bugger the adapter finally came to life and my repair successfully ended here!

Because I previously had no 3.0V zener I soldered in a 3.5V zener, why the adapter output voltage was with an output voltage of 5.2V obviously a little higher.

And my previous ‘repair’ about the super safe method on testing these small power adapters without the commonly used light bulb and unsafe live AC power line connection, came in very handy again!

After I asked my electronics friend Erik about this charger I now know what this adapter was used for. I have to replace the zener by an exact 3.0V value again because the adapter was used for charging a 18650 3.7-4.2V Creon 3W Led torch/light. It apparently got blown immediately after the Led light was switched on while it was charging. When assumably the current became too high for the charger to deliver both the charging current and the Led light current. And why my friend bought 3 extra adapter chargers to make sure his Led light always can be charged.

Below follows a photo of the working safely powered power adapter under test.

Using the DY294 also just worked but it couldn’t provide the necessary higher supply current for the adapter under test fast enough to activate the adapter long enough to be able to make a photo. Because the adapter used so much energy from the charged primary 2.2uF HV e-cap it already had discharged the moment the adapter started working.

If this adapter had a real PWM controller chip that controlled the step-down conversion from AC to DC it should have worked also good enough with my DY294. But the Omnipotence Backlight tester was again able to deliver enough current (probably at least 150mA!) which also worked on this less economic more energy consuming power adapter.

The red wires provide the DC voltage input into the AC adapter. The green and white wires are the + and ground adapter output to my DMM voltmeter.

(AC anode diode to +, other AC input -). Otherwise it won’t work because of the single rectifier diode. (not an AC diode bridge rectifier).

led backlight tester to test small power supply

I’m so glad never ever again having to connect these little power adapters straight onto the dangerous live 230 VAC power lines just to test these small charger adapters!

albert from netherlands

Albert van Bemmelen, Weert, The Netherlands

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Note: You can read his previous repair article in the below link:



  1. Gassan Ali

    January 22, 2021 at 6:54 pm

    Great work! The beauty of your repairs are that you make the effort reverse engineer the whole circuit every time. Definitely a habit that I should start practising right away.

  2. Albert van Bemmelen

    January 22, 2021 at 11:00 pm

    This little adapter pcb had so many failures that a schematic to fix the problems was most helpful, Gassan. Also because I at first had no clue what it was used for. And the lost copper tracks made it worse. Here the smps transformer was the only part that didn't fail when tested with the Blue-Ring-Tester.

    • Albert van Bemmelen

      January 23, 2021 at 3:52 am

      PS: The date on the above right in the schematic 2014.07.01 was not my date of making the drawing of the adapterboard but the marking on the pcb. See component side photo on the left. Between the 15 ohm resistor and 3.9 Mohm resistor next the 8050 right above the 400V HV 2u2F electrolyte capacitor.

  3. Lewis Spedding

    January 23, 2021 at 12:34 am

    Great work I have a similar adapter to repair and this info and insight is useful. I will reread again. I have changed all the electrolytic caps but no joy as yet! Also relaced the inductor. The surface mount components seem OKay
    Would you be interested in having a go?
    Thank you Albert.

    • Albert van Bemmelen

      January 23, 2021 at 2:40 pm

      Since you have the same adapter board Lewis, I would suggest to thorough check the copper tracks on bad connections. And also check for bad cold solder joints because there were a couple of them on my board too! Of course check the transformer first with the Blue Ring Tester because if that is failing the adapter will not work anyway! Good luck!

  4. Lynn Blakely

    January 23, 2021 at 8:25 am

    Alber: Another excellent job well done. We appreciate all the dialogue, and use of the different testers. Yes safety is very important.

    • Albert van Bemmelen

      January 23, 2021 at 2:43 pm

      I think so too Lynn but according to the dislikes I got apparently not everyone agrees?

  5. Parasuraman S

    January 24, 2021 at 12:10 am

    Very informative and thorough probing all the in and out of these small devices, that too with your unique methods! We are all lucky to have such a professor who teaches us something or other in almost every article!

  6. Albert van Bemmelen

    January 24, 2021 at 2:43 pm

    Who ever would have thought that connecting a HV tester onto the primary inputs of a small smps adapter would be that simple but never before used method? Not me dear Parasuraman!, lol.
    It is probably why we learn never to do such a thing. But when we do, it turns out that it really works as a new and safe test method in almost all cases!
    I guess we sometimes just have to think 'out of the box' to come up with something new.

  7. Amir Mukhtar AShrafi

    January 25, 2021 at 3:54 pm

    Thank you sir Jesine for Great share providing.
    Also, regards goes to Sir, Albert van Bemmelen

    Thanks you
    Amir Mukhtar Ashrafi
    Karachi. PK

    • Albert van Bemmelen

      January 27, 2021 at 4:25 am

      Glad that you liked the article and Jestine's free Blog Amir! You are most welcome! I hope you are having just as much fun in fixing things as most of us do!

    • Jestine Yong

      January 27, 2021 at 10:26 am

      Hi Amir,

      You are welcome


  8. Yogesh Panchal

    January 28, 2021 at 3:15 pm

    Thanks! for sharing another informative experience.
    Making & Studying stage wise Diagram is good practice and easy to understand the working of the particular part of the circuit.

  9. Albert van Bemmelen

    January 29, 2021 at 12:11 am

    Indeed Yogesh, a good schematic makes an already half finished repair! Like taking snapshots of any internal circuit or board in any device is by saving time on any future repairs. Especially when parts afterwards are blown or burned, and no longer can be read or catagorized.

  10. Amir

    July 1, 2021 at 9:27 am

    Thank you so much, I have a this kind of adaptor and the 220 ohm resistor completely turned to black, I couldn't read ohm, but now I can change it, best regard

  11. Aung Myo Khaing

    June 14, 2023 at 12:37 am

    I have this charger. Now charger outlet happen 3.6V and both indicator is on when charging. rated voltage is 4.2V and 500mA. So please, how to chaeck and repair it.


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