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Laptop Power Supply Repair- 20 Volt 4.5 Amp

By on August 1, 2016
repairing no power adapter laptop









Today my Croatian friend Avrim brought me his 20V 4.5A Laptop Adapter after it blew the fuses in his home with a big bang. And after which his adapter with Model number: ST-C-090-20000450CT was defect.

laptop power adapter repair

After opening the case it was easy to see were the problem on the board had occurred. The black spots on the inside of the case (Solder side) showed exactly were to look.

Next photo shows, marked with arrows, were the board outside copper track had completely vanished by the big short current that had taken place. Both circles mark the spot were also one of the legs of the 450V Primary Capacitor escaped out of the solder and the connection to the track that connects to the plus Pole of the 3 Amps Greatz Diode Bridge KBP307. And those circles also mark were the Bridge was internally completely shorted. Why also the internal primary Fuse had blown.

fix power adapter

These Power Adapters are good quality Replacement Adapters for Dell and other Manufacturers. On above photo also the Green Controller chip (8 pins SMD) GR8874 is visible. I had some trouble to find the right type Controller used here because the text on top was almost unreadable. As you also can see on one of the following photos. Probably because of some glue that had stuck it to the inside.

I replaced the original Diode bridge KBP307 by another one I could use. But I first had to adjust the Board holes and the Pins to make the larger PBL 405 Diode bridge fit. The replacement Diode bridge is capable of rectifying 4Amps at 600Volt (reverse Voltage of 420Volt), so at least the Current is 25% higher. Next photos show the Component Sides of this Adapter Board with the defect Components still in place. Both Semiconductors are Cooled by attaching it to the Alu Cooler Plates with a small Nut and Bolt. The primary Mosfet is a type SVN10N65F, and on the secondary side a semiconductor type SSBR20100CTF. They both were fine ! As also was the 450Volt primary Buffer Capacitor, after checked on its ESR value, just as its capacity. It’s incredible how much space is left on the Primary Side of this Green Controller Adapter. Maybe If they had placed the big 450V rectifier buffer Capacitor 90 degrees turned the Adapter could have been a bit less longer. But that no doubt had made the Cooler Plates shorter.

laptop adapter repair

repairing laptop power adaptor

After I had replaced the shorting Diode bridge by the PBL405 (see next Photo) I used a Light bulb over the defect Fuse to test the Circuit if the Controller still worked and nothing else was defect.

laptop power supply repair

As you can see I had to make sure that the a bit larger PBL405 would fit inside. And luckily it did! (As said I had some trouble in making the thicker and wider pins fit in this Board. And because that also made it stick out taller, it was just manageable). Following Photos show the previous smaller but now replaced Diode bridge. Followed by the bad Fuse that turned out to be a 5A T 250V type. Only visible after the black shrink Socket was removed.

And of course some photos to proof that the Adapter is working like new again !

I’ve probably said it before, and I can say it again, another repair fixed at almost no costs!

Only one Diode bridge, one Fuse, and some solder and some thin wire for the evaporated copper track were needed to repair this good constructed Power Adapter. Another repair succeeded at small costs.

And today I brought my friend his as new working 20V 4.5A Laptop Adapter back.

PS: Yesterday I learned another thing, why a Power Adapter is extremely important for an Android Tablet or Mobile Phone. If you put away your Tablet without charging in time the Lithium-Ion Battery, you will loose your Android OS Image on it. And it will get stuck in Booting the Android System. So it has probably nothing to do with your Battery going bad. But with your Tablet becoming useless. So you better make an Android Backup Image of your system or keep your Battery Full !

fix laptop power supplies

power adaptor repair

laptop no power repair

repairing power adapter laptop

Previous photo shows the open case just before closing it after the successful repair. And the 2 boards solder side photos before the last 2 photos show the board before, and after repair.

Until next time.


Albert van Bemmelen, Weert, The Netherlands.

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




  1. moshe

    August 1, 2016 at 11:56 am

    Nice repair albert..thanks for sharing!

  2. Parasuraman S

    August 1, 2016 at 12:37 pm

    Very nice!

  3. Yogesh Panchal

    August 1, 2016 at 5:04 pm


    Good attempt ! thanks for sharing.

  4. Raju Varghese

    August 2, 2016 at 12:39 am

    Hai Albert,
    Good Day!!!
    excellent job , thank you for sharing .

  5. Anthony

    August 2, 2016 at 4:00 am

    Great repair and redesign work there Albert ! The hardest part is probably opening the cases of these adapters ! Thanks for sharing your stories here.
    Kind Regards

    • Albert van Bemmelen

      August 2, 2016 at 3:50 pm

      That was no problem Anthony. Opening was almost as easy as separating
      both 'plastic' sides without using any big force whatsoever.
      Just putting something inbetween the middle of both sides all around was enough to break it open. Closing it safely is harder because the 'plastic' glue edges were only small and thin and easily broken off.

  6. Robert Calk

    August 2, 2016 at 4:15 am

    Nice job, Albert. Thanks.

  7. suranga bandara, Suranga Electronics

    August 3, 2016 at 6:09 pm

    excellent Repair, Mr- Albert van Bemmelen,

    Thank you for sharing !

  8. beh

    August 4, 2016 at 1:15 pm

    yes. another good repair and thanks for sharing

  9. Humberto

    August 4, 2016 at 10:49 pm

    Good repair Albert. Keep up sharing with us your experiencies.

  10. Luciano Khware

    August 5, 2016 at 7:33 pm

    Job well done! Keep it up.

  11. ombra32

    August 26, 2016 at 7:03 pm

    thanks also for the Android trick!

  12. Jasvir brar

    October 21, 2016 at 9:04 pm

    My Mac book adapter is not working .I cheaked diode main capacitor is OK but not any fault trace

  13. Albert Hoekman

    November 1, 2016 at 5:03 pm

    Hello Albert, finally I have time to look after the articles here. I have an original DELL power supply of 240 Watts which fails to work, do you have any experience with these things?

    Best regards and keep on the good work you are doing!

    • Albert van Bemmelen

      November 4, 2016 at 2:29 am

      I openend a Dell mini desktop Smps before. But could not repair it. The board and some parts were completely blackened. It would have been nice tot save it because the 180 Watt (?) was so compact. I may have some photos left of its internals I could mail you?

  14. Israel

    July 27, 2020 at 8:15 pm

    Thank you so much especially for the pictorial images. I have rather similar PCB board with very similar layout but couldn’t recall if a capacitor had completely blown out and off the board. Without the specs of the missing cap. I had stalled on my repair job and this was the only pictorial I could find as the schematics were not available either. Thank you so much and I will definitely follow you!


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