AC DC Adaptor fail

[DiyNutJob]

None of the capacitors are blown. So, my theory is out the window.

AC side large capacitor: CD11GA 130C PET, Power Bright 450v 6.8uF
measured 8.06uF

AC side small capacitor: Jwco -40+105C 03/22, 50v 47uF
measured 44.8uF

DC side capacitors: SD CD 263 105C-M, 35v 220uF
measured 201uF

 

[DiyNutJob]

...it's not possible to tell from the pictures, but are there any marks on the transistor (in my experience they can pop from the flat face)?

Unless the IC failed internally, there's nothing on the outside that would lead me to believe it's blown. The surface is totally flat from my feel with the finger.

 

[RandomGrinch]

As Harry mentioned earlier, if the transformer has blown, have you checked the resistance of the windings?

 

[DiyNutJob]

How do I check the transformer? It has 4 legs on the AC side and 2 legs on the DC side.

 

[RandomGrinch]

This might be the datasheet for the IC - https://datasheetspdf.com/pdf/1282478/LeadtrendTechnology/LD8115/1

Try instead an ME8115, and the schematic might look a little like:

Datasheet attached.

How do I check the transformer?

As per the schematic, check the resistances between these connections:


...and it would be interesting to know what load you were attempting to put through this little device!
Its maximum power output is 18W, and that's if the other components are suitably rated.

 

[DiyNutJob]

The adaptor is rated 24v 200mA. I am connecting it directly to a stand alone car battery. The reason I am doing that is because I had no adverse effects connecting a similar adaptor rated at 18v 200mA on a long term basis - months. A watt meter reported 1.2W going into the battery, or 5mA.

The transformer resistances are:
orange 0.2 ohms
purple 2 ohms
green 0.2 ohms

 

[RandomGrinch]

The transformer resistances are:
orange 0.2 ohms
purple 2 ohms
green 0.2 ohms

We can't really do a proper measurement of the impedance of the transformer, without some AC - but this at least shows the windings aren't open circuit.

 

[DiyNutJob]

Found it. What is that thing and how do I test to confirm? What would cause it to blow?

 

[RandomGrinch]

Found it. What is that thing

 

[Harry Bloomfield]

Found it. What is that thing and how do I test to confirm? What would cause it to blow?

It's a film capacitor. Maybe faulty manufacture, rather than any external cause of it's failure. You can confirm it with a capacitance meter, or an ASR meter..

 

[DiyNutJob]

False alarm. The apparent crack in the polyester capacitor is only visible under camera flash conditions. It's normal packaging sealed under plastic. The capacitor is marked [logo] 272 1200V. It's most likely 272J 1200V, the spec of which is 0.0027µF. I took it off and measured 2.77nF.

The fault may well turn out to be the main IC or the transformer because the remaining 5 large components on the board look unburnt and undamaged. I have to confirm they are really OK.

 

[Harry Bloomfield]

The fault may well turn out to be the main IC or the transformer because the remaining 5 large components on the board look unburnt and undamaged. I have to confirm they are really OK.

In the above photo, what are the markings on that black plastic cased item, which looks like a 3-pin transistor package - adjacent to C6?

I'm thinking, it may be a triac, and has failed..

 

[DiyNutJob]

The marking on the black 3-legged thing is: H431 BA [logo]

Here's an amusing description of how these adaptors work. He's most likely describing my 18V 200mA adaptor. I have yet to open that to see what's inside. But it works and hasn't started any fires for a year or more. It did some magic to my battery and there hasn't been any lost charge (self-discharge) for 3 months while sitting on MDF, and unconnected.

 

[RandomGrinch]

H431 BA

An adjustable shunt regulator, as per:

Datasheet attached

 

[RandomGrinch]

Here's an amusing description of how these adaptors work.

Your PSU is a little bit better than his!
You have a 'Class Y ' capacitor, when he doesn't, and the separation of the PCB tracks is a lot better!