Repair of a switching power adapter without any switching controller chip!!
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).
As in most cases I had to crack it open with a screwdriver.
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.
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).
So the only defect parts are the Fuse, Q1 and the C1 capacitor.
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.
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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