300 Watt ATX Power Supply Fixed
Today I finally fixed a Power Supply (For Home or Office use !) Model: SS-300FS Active PFC that I had looked at months earlier but couldn’t fix.
The Seasonic 300W desktop PC power supply had worked several years until it often wouldn’t start. Or suddenly did quit while working.
So I opened it and found that the Fuse still was intact. Next photo shows how easy it is to remove the pcb from the now empty cabinet.
Next photo shows the 230VAC input (dangerous side) with Graetz diodes input filters etc.
And in the following photo the safe Output side. (Black cable is FAN supply).
I replaced a defect primary Mosfet Motorola (ST) W8NC80Z by an IRFP 448. But still the Power supply didn’t come to life. And a view from the top with on the bottom left on the Cooling block the replaced Mosfet.
I also replaced an 2200uF 6.3V electrolytic on the secondary side (because it was bulged). The next photo’s show the replacement Mosfet IRFP448. (I took the Mosfet from another board so don’t look at the enhanced soldered pins. The original Mosfet still had much longer legs).
So because I couldn’t find why it still wasn’t working although all semiconductors were okay, I had put it away until today when I took another look inside and noticed a 47uF 25V capacitor that looked dirty on top. The bad 47uF component you see in the next photo’s.
When I measured the Electrolytic it was a total short circuit. And therefore I replaced it by a 47uF 50V component (it was originally an 25V volt type, but 25V extra max voltage is always better I guess!). In the next photo a better look on the 47uF now 50V replacement elco.
The component marking on the PCB was C24. (See next photo).
In the previous photo it’s position is in the top middle above the “9937” elco. (showing it’s 47uF 50V replacement). All other semiconductors I found to be 100% fine before, so I re-checked if the 47uF 25V replacement now had the success I wanted? And it did! So the next photos show the 12V and 5V resulting measurements. In the next photo you also see how I simulated the normally in a desktop pc available On switch by connecting 2 of the power connector wires with a wire. (connecting Black with Green of the 20 pole connector).
Also the 3.3V on the power connector was 100% too but I haven’t taken a photo from it, so take my word for it
And to conclude this repair I’ll show you the solder side of this Power supply!
Another Power Supply fixed, and this time it was a 300Watt pc desktop power supply with almost zero cost!
Hope you liked it !
Albert van Bemmelen, Weert, The Netherlands.
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