AC DC Adaptor fail

[DiyNutJob]

My latest arrival of an AC/DC adaptor failed. I only played with it for 5 minutes and it's gone. I don't feel I got my money's worth and hoping to play with it some more. Any electronics experts here who can help me diagnose? It's within my ability to replace larger components. I don't have the tools to deal with the micro stuff. This is my first ever electronics DIY and know very little to nothing.

It looks like a simple device with few components. I have tested all the diodes to confirm they are OK. The fuse is fine. While it worked, the LED light came on as soon as I plugged it into AC. Now, it doesn't come on, and there is no DC output. Although the LED will still come on if there is power coming from the DC side. I can turn it on with my multimeter's power while testing the diode beside it. The LED is at bottom left of the first image.

The adaptor failed after an almost inaudible pop. I can see no burn marks anywhere, and none of the capacitors looks exploded. The following images show DC output on left and AC input on right.

 

[RandomGrinch]

Your front picture hasn't posted for me.
Theres nothing obvious on the back of the PCB, that I can see.

...but I'm definitely not an expert!

 

[DiyNutJob]

Don't worry, I'll take info from anyone. But, it doesn't mean I will use the info. Here's the front, LED and DC on left:

 

[Diver Fred]

My first thought is the IC has blown. Any lumps, spots on the upper face of the IC?

There is a lot of noise inhibiting company missing.

 

[DiyNutJob]

The big IC is 8115E 2131. The top surface is totally flat. From a certain angle, there is very very faint water/burnt mark. This might not be anything. From certain other angles, the model engraving/marking is perfectly clear and the stain is not visible in that angle.

The small IC is PS 817C 2N26. No noticeable stain on that.

 

[Harry Bloomfield]

My first thought is the IC has blown. Any lumps, spots on the upper face of the IC?

I agree, either that or the transformer has gone o/c. Cost of getting the parts to repair it, unless it is something unique, will far exceed the cost of a replacement.

 

[DiyNutJob]

In this repair video, the fault was a capacitor with hidden damage. It's possible I have one, and this could explain the pop noise. I presume nothing else would produce a pop.

 

[Harry Bloomfield]

It's possible I have one, and this could explain the pop noise. I presume nothing else would produce a pop.

That's the first mention of a noise...

Many components can make a noise as they let the smoke out.

 

[RandomGrinch]

I presume nothing else would produce a pop.

As above, other components can pop.
Although usually there are some telltales on the component and PCB:

That's the first mention of a noise...

Not quite

The adaptor failed after an almost inaudible pop

...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)?

 

[DiyNutJob]

Theory: at the moment of the pop, I was jamming 24V into my standby 18 year old car battery. I could hear the electrolyte bubbling, and knew it wasn't working to the way I wanted. Then the whispering pop brought the experiment to an end.

On the DC side, under one of the two capacitors, fresh bare copper of the PCB pads are showing where solder should be. I am guessing the solder was blown "CLEAN OFF", eastwood style by the exploding capacitor as the battery resisted high voltage charging. The arrows indicate the bald spots around the capacitor legs. Initially, I assumed that was caused by poor factory assembly.

 

[RandomGrinch]

one of the two capacitors, fresh bare copper of the PCB pads are showing where solder should be.

Interesting, that wasn't obvious from your first pic.
Desolder it and see what happens!

 

[Harry Bloomfield]

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

8115E 2131 - The 2131 means manufactured 2021 week 31 of the year.

The PC 817C seems to be this - https://datasheetspdf.com/pdf-file/952198/KeepJump/DPC-817C/1

It's an opto-coupler, provides voltage output feedback, to control the LD8115

 

[Diver Fred]

I wonder if there was a 'surface mount device' solders between the 2 flagged solder pass that has blown off.

 

[RandomGrinch]

WeI wonder if there was a 'surface mount device' solders between the 2 flagged solder pass that has blown off.

It doesn't mean there wasn't a component there, but there isn't a silkscreen for one.
The connection is from 0V to +V on the output, so if a component was missing there, it would be of little consequence anyway - the failure of the PSU would still be elsewhere.

 

[DiyNutJob]

I wonder if there was a 'surface mount device' solders between the 2 flagged solder pass that has blown off.

I don't know. Is it normal to have an SMD connecting the 2 legs of a capacitor?