Blown component on circuit board

This charger runs on 3 volts DC. I accidentally plugged in a 12vdc power supply that had the same plug shape. There was a puff of smoke and a burning smell. So I unplugged it quickly. Later, I took the charger apart and the only damage I can see is a blown component on the circuit board next to the line-in. It appears to have been a cylinder about 1/4" in diameter and 1/2" tall and contains a bunch of soft brown fuzzy material which can be seen in this photo:

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Here's a picture of the exploded shell that I pulled off the two aluminum tabs sticking up from the black circular base.

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The label seems to say "-40C + 105 C" and "SR LOW ESR"

What would this have been? A capacitor? A fuse? And where could I get something to replace it? Or could I just solder the two tabs together and see if it still works (but without fuse protection)?

I desoldered the blown component and removed it from the top of the board but there are no traces there.

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The underside of the board looks like this:

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The speckles are remained bits of solder after my amateurish desoldering job. ;-)

Here's my interpretation of what the various soldered connections are (you'll have to click on the image to zoom in to see the outlines and text I added):

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So it looks like the blown component was straddling the two sides of the power. Would it have absorbed the over-voltage and protected the rest of the circuits and components? I'm not seeing anything that looks damaged though I suppose it would be hard to see if the IC under the black disk had gotten fried. Is there any way to test it?

Strangely, these JPG's are both rotated counter-clockwise 90 degrees on my computer.

Thanks for your help.

Gerard

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@gerardm Gerard, use this link to see how to add your photo, it will help ifixit volunteers ans. your question.

Adding images to an existing question

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@gerardm that looks like leftover capacitor parts. No you definitely do not want to solder those tabs together. Is there any chance you can take a picture straight down of the board, as well as both sides of the board? It'll make a difference if we can see how those components interconnect.

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Definitely a blown cap

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Absolutely a blown capacitor. I believe the value was 560uf at 10v. You'll notice the dome shape on the top of the old capacitor (with the cross or plus score on it). If any capacitor top is not flat, it is failing or failed.

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Hi, On the lower picture of the blown capacitor, (I pretty sure that is what it is) I can just make out on the bottom edge of the capacitor, something "uF" If you can see what is written in front of that we will have the value of the capacitor in microFarads. Also given that the cap shown next to it has a voltage working value of 25V there is a fair chance that the blown cap will have the same voltage rating. i.e. xx uF, 25VW, -40 +105C low esr.

If you have an Ohmmeter connect across the two pcb board connection points of the cap and see if there is a low reading. Reverse your meter leads to check the readings 'both ways'. It may be that you get a low reading with the meter leads in one direction but hopefully not in both directions as this would indicate a s/c somewhere. In one direction only may be OK as you may be looking at a diode or other type of semi conductor device.

If you do find the value written and can find replacement part online order 2-3 as if you replace it and it 'goes again' due to more problems further into the circuit then at least you have a spare handy once you have found the problem.

Also just wondering, you said it worked on a 3V charger. Was this a negative input or positive input charger, i.e. -ve leg on centre pole of plug. If it is a positive input then 25VW caps seems extravagant by the maker as there are 16VW ones. Just a thought.

Update (11/16/2016)

Hi @gerardm,

Not good news I'm afraid. It means that something else has 'blown' in the circuit. Check for evidence of heat stress or cracking in the IC type of components close to where the capacitor was located.

Here is an image to give you an example. It is NOT of your particular circuit

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Imagine that C1 is your faulty capacitor. With the Ohmmeter across its' connections in one direction you may get a reading thru the path of C1 > IC1 3-1 > R2 >R5 >R1 and back to C1 when you have the leads in that direction and when you reverse the leads because IC1 is now 'dioded' there should be no path thru IC1 1-3, or at least it should be a very much higher resistance reading than the other way. There should also be no path through C2, Q1 or IC1 3-2 or C3 BUT because the 1st path mentioned before is in parallel with these components it is a bit hard to tell without isolating parts of the circuit.

Essentially what I am saying is that there most probably is a voltage regulator in your particular circuit that has gone s/c (short circuit) that is why you are getting the same reading in both directions. One way to find the problem is to start at one of the capacitor connections and trace the track to the next component, remove the one leg of that component from the board and then measure again to see if it still measures the same in both directions. If the track 'finishes' at a component, it means that the circuit continues through that component. If it is a regulator IC (i.e. not a capacitor or resistor or mostly anything with two 'legs' - I know diodes only have two legs) then you have to remove it and test between the usually three 'legs' e.g. in the example of IC1 you should read low resistance between 3-1 and 1-2 but not between 3-2 and also not when you reverse the meter to read between 1-3 and 2-1 and 2-3.

Alternatively the quick way is to remove each regulator type IC, close to the failed capacitor location from the board and measure it out of circuit to see whether it is OK or not. if you find a faulty one that still doesn't mean that that is the only problem as other components may have failed as well but it is a start as you can then look at the other components directly associated with the 'failed' regulator (it that is what it the problem) and check them as well rather than having to go through the entire circuit.

So good luck and unless there happens to be a circuit number printed on the board that you can use to find the circuit online to make it easier to fault find, then "Welcome to the world of fault diagnosis and repair at component level in electronic circuits without the aid of a circuit diagram".

,

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I agree with your assumption on this one. Personally I'd go and replace this cap with a 100UF 25V electrolytic one. Most charger schematics I have use that one as a filtering cap. Should work well for a 3V charger.

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Thanks everyone for your helpful comments. I'll try to find the text on the remnants of the capacitor and then find one to try out.

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I measured the voltage of the power supply; it is a cylinder style plug that goes into the female on the board. it is giving +3.20 volts with the red leads connected to the center lead and the black lead against the outside of the shell.

I also measured the resistance across the power leads (and across the capacitor attachment points; same readings) using my digital meter and I got 77 (on both the 2k and 20k scales) in both directions. Sometimes it was as high as 81. But the most frequent value was 77. So no difference in the direction. What does this mean, @jayeff ?

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@gerardm does not mean a whole lot. You replaced the capacitor? What happened after you did?

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I haven't had a chance to find a capacitor yet. From the previous comments I thought it likely there was further damage so not worth trying. Thanks for your comment; it will encourage me try replacing it.

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