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Repair of a switching power adapter without any switching controller chip!!

By on May 2, 2015
power adapter repair








Nowadays most switching regulators are controlled by some kind of Pulse Width Modulated (…GREEN) controller IC. But here’s an example without any controller chip. The adapter is a SUNNY 12Volt 1.5A 18W power adapter for 100-240VAC (Made in China).

power adapter repair

As in most cases I had to crack it open with a screwdriver.

power adapter repair 1

The above photo shows the primary dangerous side of this adapter. Above the blue and brown power input wires there is the defect T1A 250A Fuse next to the green filter capacitor. On the left the internally completely short circuited and removed 13007 High Voltage defect NPN transistor is shown.


The only other active component on the primary side is a 8050S transistor in TO-92 3-pin housing. It is a low voltage High current (up to 700 mA) small signal NPN type transistor.

power adapter repair 8050s transistor

The above photo shows Q2 transistor 8050S and the previous position of the now removed Q1 transistor 13007 (MJE or SBP). On top of Q2 was the now also removed C1 47uF 400V electrolytic capacitor. (Because it was bulged and didn’t act as a capacitor anymore).

power adapter repair bad components

So the only defect parts are the Fuse, Q1 and the C1 capacitor.

power adapter pcb board

The above photo’s show the pcb solder side. But how does this adapter work without any controller IC? In the next photo the Primary Transformer connections are numbered 1 to 4.

power adapter repairing

Measured with a digital meter it revealed that Transformer pin numbers 2 and 3 internally are a coil, and numbers 1 and 4 also. The open solder holes marked by the text R22 was the position of the now Bulged 47uF 400V elco. And on the right of diode D5 was Transistor Q1 mounted. So this adapter probably switches with the 2 Transistors Q1 and Q2 into the 2 primary coils.

And Q2 was still 100% okay, so it probably triggers the current primary to switch the special HighVoltage Q1 13007 NPN ! And this adapter therefore doesn’t need any controller chip. The white plastic in the above photo protects originally mounted the optocoupler as some kind of shield.

All other components are okay. Which means that this repair is an easy one and because I don’t need any controller probably also a cheap one ! The only difficult part is how to glue the plastic together safely again! And I use (no advertising intended since I don’t get paid from the Glue factory Haha) Uni-Rapide Super Gel from Pattex for this because it doesn’t drip and glues fast and secure!! And if I need to correct (straighten) the plastic sides a bit, I use also a hot air gun before glueing the case together. Another switching Power supply repaired !

This article again shows that almost every – Big or Small – Power supply can be fixed !!

Albert van Bemmelen, Weert, The Netherlands.

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  1. Yogesh Panchal

    May 2, 2015 at 1:48 pm

    congratulations for this fix and thanks for sharing.

    • Albert

      May 2, 2015 at 5:48 pm

      Thanks Yogesh. Glad you liked it!
      For additional information about the mentioned HV NPN E13007 : 10 of them cost about $3.98 US on E-Bay.


  2. gcharal

    May 2, 2015 at 6:26 pm

    Good repair!!

    But did you identify what cause the failure at first?
    Is there an overvoltage surge for example or the
    use used the adapter with a wrong device?

    Thank you again.

    • Albert

      May 2, 2015 at 9:39 pm

      Hi Gcharal,

      I really couldn't say how it got broken. Most repairs I get for free from friends or did find in the garbage at work or other places. And that doesn't mean it can't be fixed.

      Most Power Supplies at work I know were vastly abused beyond normal conditions. We for instance used them to burn out shorted capacitor's on Desktop or Laptop Mainboards. You see because those capacitor's had many parallel components and to desolder all out was too risky and too much work !! So the bad component would burn out (go up in smoke) in real time after a big power short circuit current from our power supply. Or became hot (a bad capacitor acts as a unwanted resistor !) and was detectable this way ! Unfortunaly this sometimes also meant the end of a few Power Supplies that couldn't stand the test!


  3. Maurizio C.

    May 2, 2015 at 7:42 pm

    Sorry, I did not clearly understand WHAT components give proper pulses to the base of the primary transistor in your switching power supply

    • Albert

      May 2, 2015 at 9:19 pm

      Hi Marizio,

      Primary the transformer only seem to have 2 coils. One coil was low impedance and the second primary coil was high impedance (checked with the fantastic Blue Ring tester from AnaTek Corp.USA !). And as said in the article there are only two active Transistors in the primary circuit. One is the now defective HV NPN E13007 (8A/700V) and the other the 700mA High current 8050S transistor (still intact here!). And with the passive components on the solder side they make some kind of oscillating primary circuit to generate Secundary induced Energy.

      Since the 1AT fuse was defect too, as also the E13007 and the bulged 400V elco were, it is an easy repair. Else the transformer surely was melted beyond repair.

      If you want to know how the primary circuit exactly operates you could draw the circuit from the given parts on the pcb.

      Hope this answers your question?


      • Robert Calk

        May 3, 2015 at 8:40 pm

        Good job Albert. I was going to ask you if you used the fantastic Blue Ring tester to test the transformer! DMM's are not good enough for proper testing since you can have an internal short and not know it just using a DMM.

  4. Gary

    May 2, 2015 at 8:46 pm

    Good job in the repair. I have found quite a few bad 13007's in electronic fluorescent light ballasts over the years. If you purchase the ON Semiconductor (Formerly Motorola Semiconductor) MJE13007, they seem to be higher quality and last longer. Also, many times with the light ballasts, they are only clipped to the thin sheet metal chassis with no thermal compound. So the MJE13007 may last longer due to proper thermal management as I install them correctly.

    • Albert

      May 2, 2015 at 9:27 pm

      Thanks for your comment Gary.

      I don't know what parts I will recieve from China manufacture-wise. I hope it's the better ON-semiconductor component as you said.
      The small cooler had no thermal compound on it but only a thermal conductive pad in this repair article.


  5. beh

    May 2, 2015 at 10:12 pm

    good job weld one

  6. Ekundyor

    May 3, 2015 at 5:02 am

    That is grate! I have learned a new lesson.Thanks for the explanation.

  7. Ehsan Murad

    May 3, 2015 at 12:07 pm

    Thank you for sharing

  8. Florin

    May 4, 2015 at 2:16 pm

    I think the key for the exclamation point on your keyboard is worn out from heavy use...

    • Albert

      May 6, 2015 at 4:41 am

      Did you count them ?

      Think of them as KA-CHING! and you're rich Haha !
      But I'll try to chill on the 'you know what' if it makes you feel better...

      Have a nice day Florin EXCLAMATION POINT.

  9. Humberto

    May 4, 2015 at 8:07 pm

    Congratulations Albert, with your repair another PSU was saved from the dump.

  10. Chris

    May 5, 2015 at 1:48 pm

    Good job Albert!

  11. sam montero

    May 5, 2015 at 9:02 pm

    Hi Albert
    The way you described the circuit, there is three active components.This is 13007, 8050 and the optocoupler with a txtor on the primary side.
    The 13007 you could get it free from a defective electonic balast lamp. Just a tip.


    • Albert

      May 6, 2015 at 2:39 pm

      Hi Sam, you are right of course to also name the opto-coupler an active component. But it doesn't oscillate energy into the primary coil and also is part of the secondary circuit. But indeed if it is defect nothing works, also when the txtor is on the secondary side is defect.

      I have found a really easy tester for the optocouplers. See for instance this link on Ebay for this great hardware tool:
      (No shipping costs either ! And also very affordable).

      It works on only one NiMH battery and also can test nearly all your TTL/CMOS or Leds and Displays, and even some other parts like Op-amps and Amplifiers!

      I bought it a few months ago and think it is a terrific very portable peace of hardware to help in the aid of checking these special Power Supply components.


  12. Lee

    May 6, 2015 at 8:39 pm

    Nice repair and thanks for that "Uni-Rapide Super Gel from Pattex" quick glue tip.
    What other crazy glue would you guys recommend? I need a good brand in bottle and not the tube type that drip, dry and is "one time usable"...


  13. Taring K Arioka

    May 14, 2015 at 12:54 am

    It is good to learn that it is possible to draw diagrams from the pcb. I will try that. Hope it will be quite easy.

    • Albert van Bemmelen

      October 18, 2015 at 4:43 pm

      Probably the best way I do it, is by first drawing the positions of all components onto a new white sheet of paper. And next use another pencil or another colour to add the copper layout connections to it. This way you have an exact copy of your electronic device you are repairing on paper, in which you also can add all component's values. And when you are ready with this you are also able to draw the circuit with the components in it with their electronic symbols. From which you easily can see how everything functions.


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