12v DC adapter repair

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BoonChai

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My AC to 12vDC adapter was blown and after opened the case I found that the coil was blown to pieces by pieces.
Since I don't know what is that coil looks like ....
Is it possible to replace with any coil or need to replace with specific coil?








Your help is very much appreciated.
 
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I would say almost certainly that's not the fault - that's just an extra part which has been destroyed by the power supply failing.

The destroyed part is either a fuse, a surge limiter, or both - it's unlikely to have been a coil.

The reservoir capacitor is visibly domed, so almost certainly is faulty, and presumably the large transistor (or IC?) will have gone S/C, and thus blown the fuse/surge limiter. Other parts may have been destroyed as well, such as Q1 and the diodes in the bridge.
 
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Nigel Goodwin , Thanks for your reply.


Nigel Goodwin said:
The destroyed part is either a fuse, a surge limiter, or both - it's unlikely to have been a coil.
Click to expand...
Did u mean that the coil has nothing function in the circuit? Without that coil connection the circuit is not complete.
Can I just put the coil from other circuit?
Nigel Goodwin said:
The reservoir capacitor is visibly domed
Click to expand...
I did notice and need to replace.

Nigel Goodwin said:
the diodes in the bridge.
Click to expand...
That 4 diodes also blown and need to replace.

Replacing cap & 4 diodes will make it work?
 
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BoonChai said:
Nigel Goodwin , Thanks for your reply.



Did u mean that the coil has nothing function in the circuit? Without that coil connection the circuit is not complete.
Can I just put the coil from other circuit?
Click to expand...

It's not likely to be a coil (it would have no function), it's either a fuse, or a surge-limiting resistor, or perhaps a surge-limiting thermistor.

BoonChai said:
I did notice and need to replace.


That 4 diodes also blown and need to replace.

Replacing cap & 4 diodes will make it work?
Click to expand...

No, you need to replace everything that's blown - and it's very likely that at least the transistor is.
 
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It looks like when cap blew its electrolyte leaked around the 4 diodes,
eg stain on left side leads. They may still be OK, just use an ohmmeter
on diode resistance setting or 200 ohm scale to check.

Diode Testing: A Comprehensive Guide for Beginners

This article provides a comprehensive guide to testing diodes, including the different types, components, how to use them, and troubleshooting common problems.
www.nextpcb.com


Regards, Dana.
 
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tepalia02 said:
Doesn't the symbol look like an inductor, sir?
Click to expand...

It has a look of one, but it wasn't one - no point whatsoever in an inductor being where a fuse (or surge limiter) needs to be. At a 'guess' it was probably a fuse, and they didn't have a suitable PCB symbol for the wired in fuse they were fitting, so just chucked a symbol for an inductor in, as it was the same size.
 
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Nigel Goodwin,​

I found the culprit which is Q2, 3 pins of that Q2 is loosing from the board.
And that might cause the blown out.


I replaced the cap and 4 diodes, re-solder the Q2.


And as you suggested I install the 250v 0.5A fuse. Not enough place at front, so I put it at the back.


And guess what, the adapter is working again.

Nigel Goodwin said:
It's not likely to be a coil (it would have no function), it's either a fuse, or a surge-limiting resistor, or perhaps a surge-limiting thermistor.
Click to expand...
Thanks for your amazing trouble shooting skill.

Nigel Goodwin said:
At a 'guess' it was probably a fuse, and they didn't have a suitable PCB symbol for the wired in fuse they were fitting
Click to expand...
Sometime can't trust what they printed on circuit board especially make in china.

Thank you again.
Your help is very much appreciated.
 
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