65 Watt Autovoltage Laptop Power Adapter Repair

By on February 9, 2018
power adapter schematic












This repair is about an 65W special autovoltage laptop adapter from manufacturer Trust.

laptop adapter repair

Trust laptop adapter repair

It was from my good friend Adri’s old second hand laptop he had bought which was also the reason why he didn’t have the original adapter that originally came with it.

His laptop was okay when tested with another adapter but the Trust autovoltage adapter wasn’t.

power ic part number

I examined the primary components of the board. The biggest problem was at first not being able to determine what PWM SOP8 controller was used. Because any chip code was hardly readable. Previous photo only gave enough information after I used my Traveler USB microscope and adjusted the contrast and color settings a bit in Photoshop afterwards.

It was a B29498, B2203CP. But to be sure I needed to establish if that controller chip existed and still could be obtained. And searching for number B29498 resulted in nothing useful. But apparently a type B2203CP is definitely a PWM Controller. It in fact is an OB2203 Quasi-Resonant Flyback chip from manufacturer ON-BRIGHT.

And after comparing the chip pin functions with the schematic I had drawn, I was almost 99% certain that I needed to order that SOP8 chip. And also a new N-channel mosfet SMK1060 because both components were defect. Below one important page of the OB2203CP chip datasheet followed by a datasheet of the mosfet SMK1060 that is controlled by the OB2203 and normally provides current to the primary of the Transformer. It took me a while before I finally found a seller who provided these OB2203 controllers. And apparently others already were out of stock. So I was more than happy that the only seller I could find still had some in stock. And that being said I wondered if anyone ever succeeded in placing another pin compatible type of PWM controller chip instead of the original controller? Anyway I ordered 10 of them for 2.72 euro. And 20 x SMK1060 did cost 6.63 euro.

Not only the mosfet and the controller U1 were defect but also four in parallel connected resistors type R750//R750//1R00//1R00 smd R24 to R27 in the connection between Source and gnd (min pole

e-cap). Which makes it a safety current limiter of 0.2142857 ohm. Equals 1 / (14/3) which gives 3/14 ohm. And because every resistor that breaks open limits the current more it is safer than 1 resistor.

smk1060f datasheet

power adapter schematic


Above schematic explains a lot. After the controller chip U1 was removed I could measure an open voltage of about 34V DC on the VCC pin 6 of the controller solder pad. Which is correct and will be limited to a lower working voltage when a new controller chip is placed. The Trust autovoltage selector adapter board was rev 1.0 20091120 SMP-65WUSB (with extra USB connector secundair). Next photos show more of the primary parts of the adapter.

power adapter parts

power supply circuit board

power ic fault

power ic faulty

smk1060 fet

how to fix power adapter

how to fix and repair power adapter

After the photo with the primary N-channel SM1060 mosfet, all next photos are from the secondary adapter side. Notice the nice external 5V USB connector at the secondary safe side of this adapter. The primary plastic 4AT (slow) Fuse was still intact likely because the two R750 and two 1R00 parallel connected resistors all were blown open and no current was able to flow after the mosfet and of course the B2203 controller U1 had collapsed. Likely because of overcurrent that blew the mosfet and the controller to kingdom come. And semiconductors are the first to go compared to a slow fuse. If you want to know when you have got a N-channel or P-channel mosfet there is a simple trick to remember comparing to how we use the diode Cathode Negative- Anode Positive rule. A diode conducts when the Cathode is negative to the Anode. If we look at the arrow in the symbol of the mosfet in the datasheet of the SMK1060 we see it points to the substrate of the mosfet. And it only conducts if the substrate is negative like the arrow in a conducting diode. So it is a N-channel.

All parts on the secondary side were fine after I had replaced U1 and mosfet SMK1060F. I previously only started to examine the secondary 45NQ10T which was fine. And after I had replaced both U1 and primary switching mosfet SMK1060F, the blue power led worked nicely and I could measure a perfect 19V again!

I was very glad that my conclusion in finding the right controller chip was correct because already before ordering these I was able to match the circuit with the datasheet of the controller OB2203 U1! And I hate to just gamble and ordering parts that I afterwards do not need. But I had to order 10 of them, which means that I still have nine of these OB2203 controllers left. It is questionable that I will need them again soon. But having spare parts at hand is the life of a busy repair-engineer.

Checking all parts of this adapter’s secondary autovoltage circuit would have been a real time consuming process and luckily the primary side of this and other adapters are a lot easier to fix.

The only thing left to do now is finding a good replacement for those tiny R750 and 1R00 smd resistors R24 to R27. Here a snapshot of those now defect smd resistors after they were removed.

bad smd resistor

And my good friend will be able to use his laptop again with this special Trust autovoltage power adapter.

P.S- The original mentioned broken open resistors R24 to R27 (type R750 and 1R00) were about 3.2 x 1.4 mm. So must have been 1206 packages. And today I ordered those in 1206 and in 2010 5mm x 2.5 mm format.


Albert van Bemmelen, Weert, The Netherlands.

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





  1. Parasuraman

    February 9, 2018 at 5:50 pm

    Efforts can only be compared to a rescue operation of a baby trapped in a deep water pipe! Great job and concrete solution! A very good schematic. Million thanks for the wonderful article!

    • Albert van Bemmelen

      February 9, 2018 at 10:43 pm

      A funny and also a bit disturbing expression but I get the picture dear Parasuraman. Luckily I never throw the baby out with the bathwater (LOL). A billion (million to the exponent 2) thanks for your too kind comment back.

      • Albert van Bemmelen

        February 13, 2018 at 3:08 am

        I got confused by those large numbers Parasuraman and stand corrected: One Billion is 1 Million x 1 Million in the UK (10^12) which is 1 Trillion in the USA. One Billion in the USA is 1000 Million.
        One Dutch Biljoen is 1 Miljoen x 1 Miljoen (10^12 like in the UK).
        I wrote 1 Billion equals a Million to the exponent 2 but that of course still needs to be (1 Million)^2 or still be multiplied by 10 for 1 USA Billion, or be written as (1 Million)^2 in USA for one Trillion. It shows how easy it is to confuse EXP with ^. 2EXP2= 200 and 2^2=4 (;)

  2. Anwar Shiekh

    February 9, 2018 at 8:49 pm

    The quasi-resonant approach to SMPS is quite amazing.

  3. Albert van Bemmelen

    February 9, 2018 at 10:52 pm

    I knew it was a special controller Anwar, but I first found a confusing circuit with the OB2203 in it where it was switched on by another special chip through pin 7 PFC/VCC. And here it wasn't used so that reassured me somehow that I indeed had found the right controller.

    • Albert van Bemmelen

      February 10, 2018 at 5:55 am

      Here the link to that circuit of the OB2203 used with a second chip OB6563 chip connected to pin 7 of the OB2203CP. See:

  4. Robert Calk

    February 9, 2018 at 11:01 pm

    Nice work Albert! Another device recued from the garbage can.

    • Albert van Bemmelen

      February 10, 2018 at 10:15 am

      Thanks Robert. It was helping out a friend again, so more pro-bono work as we could say. I'm happy if my replacement parts are compensated for.

  5. Albert Hoekman, Tiel NL

    February 10, 2018 at 2:34 am

    Hi Albert, good action to repair faulty electronic equipment and not throw away in this discard society. Let's keep them running!

    • Albert van Bemmelen

      February 10, 2018 at 10:16 am

      Indeed that is always our goal Albert! And I am almost sure that the 1S_BMS_lithium_18650 module will help to achieve this.

      • Albert van Bemmelen

        February 10, 2018 at 5:28 pm

        Oops Albert, that module was only mentioned in my previous article. (I did 3 articles in a very short period of time which explains the mixup comment )

  6. Anthony

    February 10, 2018 at 4:23 am

    Wow ! Good mental gymnastics there Mr Albert in determining the right controller
    chip you needed to order and I too hate guessing and ending up with the wrong
    parts you don't need....very frustrating! The photos are terrific and your explanation
    is first class....I would be privileged to be a student in your class if you were a
    teacher imparting your knowledge. Thanks for taking the time to prepare this
    article so that we may gain more knowledge on different electronic problems
    and the solutions you present. Your tutorials are always first class !

    Kind Regards

    • Albert van Bemmelen

      February 10, 2018 at 11:01 am

      I wouldn’t mind being a teacher Anthony. I always liked that profession but sadly I’m not qualified to be one. I mainly had all sorts of not technical jobs I didn’t like and that were unhealthy to say the least. I do have my about 11 technical degrees (Dutch: Diploma’s) and also certificates, and that is at least what it takes to be able to be a good teacher in technics/electronics.
      Anyhow, with Jestine’s great repair Blog I now somehow do have a very large worldwide audience. Who ever would have thought that? not me! Thanks for your appreciation Anthony.

  7. ertuğrul ayan

    February 10, 2018 at 5:45 am

    thanks for the practical information I follow it closely I need more knowledge for success Thanks for every info gold

    • Albert van Bemmelen

      February 10, 2018 at 10:12 am

      Fixing power supplies is always a very rewarding job, ertuğrul. Thanks for your appreciation. Without it nothing works and if we do succeed in repairing the ‘black box’ we feel great. I didn’t mention in my article that it is very dangerous to work on AC powerlines. But just in case you are new to it, you must always take care never to touch anything on the primary adapter side! It is deadly and to be safer you could use a 230V AC to 230V AC (or 120V AC in case USA) safety transformer between the AC powerlines (Phase and Line) and your AC power adapter input. Also when measuring voltages on the primary side, never touch the cables of your meter. Any current could make a closed circuit through your body (your heart could stop) to electrical earth (the floor, or the central heating or via touching metal water pipes).

      • Albert van Bemmelen

        February 10, 2018 at 5:14 pm

        By-the-way: speaking about safety and about connecting to the AC power lines... be sure to here only use the n-channel mosfet SMK1060F variant. This kind of mosfet type TO-220F-3L is completely electrical insolated from having any galvanic contact with the Aluminium cooler plate after it is screwed onto it. They also sell this mosfet without the F in its name but they do not qualify to be used here!

  8. imran

    February 10, 2018 at 10:31 pm

    it was amazing the way you explained everything.
    I am not much experienced but want to learn. may be i need your help in repairing Switch mode power supplies. It will be highly appreciated.
    regards. please reply.

    • Albert van Bemmelen

      February 13, 2018 at 3:33 am

      If I can I will try to answer all questions you may have imran. Jestine's Blog is there to help!

  9. Jose Hernandez

    February 12, 2018 at 12:09 am

    Excellent article. It really explains very clearly, the repair of a laptop current adapter. I translated it into Spanish, and I posted it on my blog. https://reparandocosasdelhogar.blogspot.com/2018/02/reparacion-del-adaptador-de-corriente.html#.WoBomLPB9aS

    • Albert van Bemmelen

      February 13, 2018 at 3:24 am

      I'm proud that you took the time to translate it into Spanish Jose. Nice job and a very good way to attract more readers to Jestine's free Blog!

  10. Yogesh Panchal

    February 13, 2018 at 2:44 pm

    Good Article! Albert
    thanks for sharing.

    • Albert van Bemmelen

      February 13, 2018 at 5:25 pm

      Thanks Yogesh, no problem. With a bit of luck my next laptop 120 Watt (6A 20V DC) adapter repair will follow soon. I already replaced the power mosfet and now hope that only its controller chip is defect. I still am waiting on Aliexpress for that chip to arrive. But repair is a bit of a gamble this time because something had exploded on the solderside and inside. And I've got no clue what it was!


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