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12 volt 5 Amp SMPS Repaired
The complaint of this small switch mode power supply (SMPS) with the output of 12 volt and 5 amp was no dc output. I powered it up and test the output and indeed it was no output as seen from the photo below:
Just like any other electronic equipment with the complaint of no power, the first component to check is the main fuse. In this power supply design, it did not use the normal slow blow fuse, in fact it used a low ohm resistor as a fuse.
I checked on the fuse resistor and found that it was open circuit. From many repair histories, when the main fuse have problem, usually there will be a or some components that have shorted drawing too much current cause the fuse to blow.
After found the fuse to be open circuit, I checked on all the primary side components hope to find bad component.
My guess was right and I found a shorted power FET in the primary side and other components seems to be working fine including components at the secondary side.
I replaced the power FET and soldered a 40 watt light bulb in series with the main fuse line to check and make sure no other shorted components in the power supply once the power supply is powered On.
The result was the power supply worked again and I put in the new resistor fuse and put back the power supply casing.
I turned it On once again and saw the power LED lighted up at the secondary side-see the photo below:
Next, I used this power supply to power up the LED light chain as seen from the photo below:
Conclusion- This repair case history is pretty straight forward. What you need to know is the safety and be able to test electronic components. I can recommend Jestine Yong’s ebook in how you can be very good in testing electronic components and start to repair work. If you want to be a power supply repair expert where you can repair power supply fault fast, you can get his SMPS repair ebook here. Ok see you again in the next article.
This article was prepared for you by Suranga Bandara who owns an Electronics repair shop in Anuradapura, Sri Lanka.
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