AC adapter not working, strong burning smell

[StriderSubzero]

Hi all,

I have a 10V DC 1.2A adapter/wall wart that has stopped working. I've tried measuring the output with my multimeter and I get nothing. In addition, there was a faint burning smell. Upon opening the adapter (it has 3 tamper-resistant torx screws), it has a quite strong burning smell.

I'm seeing that the large capacitor is the most common point of failure on these, but I've never experienced a capacitor that had a burning smell, so I'm thinking it must be something else. It also looks as if the board has burnt areas on it as well.

Here are photos: http://imgur.com/a/HXh1g



Does anyone have any pointers as to what could be the matter here?


Thank you!

 

[Marcher]

Hi all,

I have a 10V DC 1.2A adapter/wall wart that has stopped working. I've tried measuring the output with my multimeter and I get nothing. In addition, there was a faint burning smell. Upon opening the adapter (it has 3 tamper-resistant torx screws), it has a quite strong burning smell.

I'm seeing that the large capacitor is the most common point of failure on these, but I've never experienced a capacitor that had a burning smell, so I'm thinking it must be something else. It also looks as if the board has burnt areas on it as well.

Here are photos: http://imgur.com/a/HXh1g

Does anyone have any pointers as to what could be the matter here?


Thank you!

Hi SS,
It is quite common for the transformer winding to burn out and go open circuit (and smell).
Check the resistance of the primary and secondary windings with a multimeter.
Sometimes there is a thermal fuse attached to the transformer that can fail.
Replacement plug-top supplies are pretty cheap these days but best to avoid really cheap Chinese types.
Some of these don't have correct separation between line voltage and output voltage.

 

[Minder]

That appears to be one of the older linear power supplies, now they are virtually all SMPS. and has already been indicated quite cheap.
If it has no output from the transformer secondary then it most likely does have a thermal fuse embedded in the winding, this was quite common on those supplies.
M.

 

[StriderSubzero]

Hi SS,
It is quite common for the transformer winding to burn out and go open circuit (and smell).
Check the resistance of the primary and secondary windings with a multimeter.
Sometimes there is a thermal fuse attached to the transformer that can fail.
Replacement plug-top supplies are pretty cheap these days but best to avoid really cheap Chinese types.
Some of these don't have correct separation between line voltage and output voltage.

Thank you for your reply. I'm really unsure as to how to test the transformer windings as I've never done this before, but moreover I'm concerned that I wouldn't be able to repair the adapter anyway, if this were the reason it failed. I'm also not sure how to open the box-like metal portion that you see in the photos.

I wanted to preserve this adapter if I could because I can't find a replacement with the same amperage and voltage outside of buying the same one. It goes to an old video game console (Sega Genesis original model) and the second-hand adapters are upwards of $20 used, and all the aftermarket adapters online are not the correct voltage or amperage.

 

[Alec_t]

I can't find a replacement with the same amperage and voltage

As long as the voltage is correct you can use any adapter which can provide at least 1.2A. I see plenty of 10V 2A adapters advertised.

 

[duke37]

The diodes appear to have overheated and burnt the circuit board. This could be due to a faulty reservoir capacitor or excessive load current.

 

[Minder]

The other thing with the linear is they usually are not regulated, they rely on the load of the component being fed to bring the voltage down to the correct value, or close to it.
The SMPS are regulated closely.
M.

 

[hevans1944]

I'm also not sure how to open the box-like metal portion that you see in the photos.

You are probably referring to the transformer steel laminations, around which the primary and secondary windings are placed (on plastic bobbins). You do NOT "open the box-like metal portion that you see in the photos."

To troubleshoot this and determine if it is repairable, you should remove the solder from where the low-voltage secondary winding is connected to the circuit board. Use solder-wick braided and fluxed copper wire to do this. Lay a length of solder-wick across the joint and heat with a 40W to 60W soldering pencil-iron until the solder melts and flows up into the solder wick. Repeat if necessary using fresh solder-wick until the two transformer wires are free in their holes and the circuit board containing the four diodes, resistor, and electrolytic capacitor can be separated from the transformer.

With the "wall wart" NOT CONNECTED to a live convenience outlet, measure the resistance between the two wires of the, now free, secondary winding. It should be a low resistance value. Measure the resistance between the "wall wart" male prongs that would normally be inserted in a convenience outlet. This should be a somewhat larger resistance value. If either or both measurements indicate an open circuit, that transformer is faulty. Usually they cannot be economically replaced or repaired.

However, assuming the resistance checks of the primary and secondary windings indicate that both windings are intact, at this point, connect a multimeter, set to measure AC voltage, across the now-free transformer secondary leads. Plug the "wall wart" into a convenience outlet and observe whether there is any AC voltage reading on the multimeter. There should be about 7 V AC. If voltage is present, the problem is on the printed circuit board: either one or more of the diodes is shorted or the electrolytic capacitor is leaky or shorted.