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Harsha Alva
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Mechanical Engineer + Software Developer
 · MangaluruIndia
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QUESTION
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Electrical Debugging

I have a 220V AC to 5V 2A DC wall adapter which I use with my Raspberry Pi. It was working really well but is having problems now. The output now varies from 4.3V to 4.8V and hence the lights on the Pi blink, but it doesn’t start. Even Android phones don’t detect the output.

I think this is due to a blown capacitor, but I’m not sure.

What might be the issue?

Any help would be appreciated. Thank you. 😃

Abhi Verma Claran Martis

Edit #1 20/3/17

The Raspberry Pi is working fine. I want to know if and how the wall adapter could be repaired.

Electrical Engineering
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Abhi Verma

Debugged electrical circuit problem. Thanks. 😃

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Harsha Alva
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Ranjan Dailata
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Application Architect/Lead Developer
 · ChicagoU.S.
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LOL. You need an electrical engineer, seriously! I thought you are debugging the PI.

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Abhi Verma
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Electronics Engineer
 · DelhiIndia
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your adapter might be a smps type. in that case if output capacitor is blown then you will not get steady output and enough current. as you said output voltage is 4.3-4.8 varying, it also shows that capacitor is blown. a smps have few key components- switch, inductor , blocking/ fly back diode, output capacitor. inductor failure may cause zero output, switch failure also have the same effect, PWM failure may cause 0 again, diode failure may cause lower voltage (can be same as yours), and capacitor failure have exact same effect due to no storage of power.
if you wanna repair that then you have to debug the whole circuit, bcoz in these kind of devices, failure of one component can fail the another component.
My advice will be to buy a new one. but if you wanna repair that then follow some steps for safety.
i have worked with 3KW smps modules and also faced so many failures as an service engineer. I always replace the faulty component and then cross check every other components related to particular ckt to avoid any future failure. after repair first test the voltage , put the ckt under test load(can be anything not expensive- lihghts, resistors load etc.). only then go with expensive devices.

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Harsha Alva
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Mechanical Engineer + Software Developer
 · MangaluruIndia
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This looks like a phone charger but it used to give proper 2A. I have purchased another one now. Wanted to debug just for knowledge.

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Abhi Verma
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Electronics Engineer
 · DelhiIndia
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Actually these cheap smps chargers works on self oscillating ckt to generate pwm signal. many times this ckt fails due to high voltage or surge at transistor or resistor failure. that makes it difficult to repair. but some of them have tiny ic to regulate the output. they are so small that i never read anything on them. just hope that these tiny components are safe. anyways gud luck.

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Harsha Alva
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Mechanical Engineer + Software Developer
 · MangaluruIndia
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Thanks Abhi Verma. I won’t be doing this as I’m terribly afraid of current shocks while debugging. Also, not worth the effort.

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Abhi Verma
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Electronics Engineer
 · DelhiIndia
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LOL! don’t be afraid. this work is risky but i do it all the time, not that bad just needed to be aware what are you doing. anyways it’s good to not deal with it , if you are not sure. just like i can’t get into mechanics😉

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