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How To Repair 12VDC Output Power Adapter
I’d got a call from my friend with the complaint of his Set top box was not working. During the conversation I came to know that he was watching some TV shows and suddenly he heard cracking noise from the TV side and the TV was showing “no signal”. This means the set top was not working (no power LED lights on) causing the TV to show “no signal” symptom. So I asked him to get the Set Top box adapter to my workshop for further testing.
Next day he visited my workshop with his power adapter. As I am sure about the culprit I have directly opened the adapter and started visual inspection. Visually checked found ok from the component & solder side of the PCB there was no dry solder as well no burning marks.
From component side I have tried to locate Fuse but there was no fuse, so I have traced the circuit from main line wire; there I found one resistor connected in series on main line this resistor showing 10 Ohm as per color band on it (Brown Black Black Gold) . So I have checked with multimeter on the circuit it shows no reading that means resistor was open.
After removing the resistor I found damage mark on resistor-see the photo below:
Again checked with multimeter and confirmed the resistor was open circuit. The function of this resistor is to act like a fuse and this is why you can’t find any fuse in this power adapter.
The corresponding components could have fault also thus connected a 60w bulb in place of that resistor which I have removed. After plugged in the AC source to the adapter, the 60w bulb did not glow and the power LED was working. Next I checked the output voltage and it measured 12.39V DC which mean it was good-see the photo below:
Once I got the correct output voltage, this means there was no other shorted components and now I can solder the replacement resistor to the circuit.
Now the power adapter is back to the life again. If you would like to learn how to repair switch mode power supply, I suggest that you check out Jestine’s ebook in power supply repair.
This article was prepared for you by Yogesh Panchal who works as a Computer Hardware Engineer in Mumbai India.
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Note: You can check his previous repair articles in the link below: