Laptop Power Supply Repair- 20 Volt 4.5 Amp
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.
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.
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.
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.
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 !
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: