Fried speaker component - replaceable?

[Ommatoiulus]

Hello people,

I picked up a small second-hand speaker with 'Aux' input a while ago to use in my car. I tested it today and it worked neatly both on batteries and with a power cable from USB to its 4.5V port.

Fatefully, I also had a cable going from a car 'cigarette lighter' plug to a connector that, with an adaptor bit, fit the 4.5V port. Stupidly overlooking that the car lighter socket would give 12V, I tried that cable. Result: a hissing/frying sound. Turned off the speaker but was left with a slightly smoking and smelling, and soundless, device.

I know very little about electronics but had a look inside. There is a metallic rectangular component (Integrated Circuit or something else?) which seems to have fried, judging by its smell:


The led is still shining when 'on' both from batteries and USB power, and a multimeter gives about 4.4V between various points, e.g. between the 'feet' of each black cylinder (capacitors??), and on the two speakers themselves (between the attachment points of the black and the white wire, and between those of the red and the yellow wire).

I'm guessing the thing might still be receiving power OK, but the fried larger metallic bit is involved in actually channeling the sound? Is that part possibly replaceable?

Or is it likely that other bits are also damaged and it's a total loss?

Pardon my clumsiness/ignorance, and thanks for any insights.

Here's the innards:



and the other side:

 

[H2814D]

Hard to tell from your pictures, but that capacitor at C8 in your third photo looks like it may have been damaged by the excess voltage. It would make a hissing sound, smoke, and the smell you have described. Do you know how to check it?

 

[Bluejets]

yup...bin it.

 

[Ommatoiulus]

Thanks for the replies!

Hard to tell from your pictures, but that capacitor at C8 in your third photo looks like it may have been damaged by the excess voltage. It would make a hissing sound, smoke, and the smell you have described. Do you know how to check it?

It's the first thing I suspected on opening the case, as the burnt smell comes from that side of the board and there's a sort of white fuzzy patch on the capacitor (visible in photo). But then (1) I read that a fried capacitor would (typically?) have a 'popped-up' end like a tin can with spoiled food, which is not the case; (2) I found the 4.4V between the capacitor's legs (but that may not mean the capacitor is ok?) and (3) the flat metallic rectangle on the other side of the board smelled even stronger.

Perhaps both components are fried. I suppose the capacitor could be replaced? Any chance for the rectangular bit?

yup...bin it.

Oh :[ Yup to what? "Likely that other bits are also damaged and it's a total loss?"

Thanks again folks.

 

[H2814D]

Capacitors are cheap. I only see two electrolytic style capacitors on that board. Find the same values and replace both of them. There is no guarantee it will fix the problem, since the excess voltage that caused the problem may have done damage to another component(s), but "binning it" won't fix it either.

That metal plate appears to be a heat sink, or a shield of some type, but the markings on the board under it show there are small surface mounted capacitors underneath it. If you can't see under it to tell what the components under it look like, it would be hard to tell if any of them were also burnt. If you can remove the plate, since it appears to be soldered to the board, you might be able to. There may be other components (voltage regulators, etc.) under or attached to that plate that may have been damaged. Oddly, however, I don't see any circuit traces that may attach to anything under it if it is, in fact, being used as a heat sink. You need to see what is under it first.

 

[Ommatoiulus]

Thanks a lot for the guidance, H2814D, much appreciated! I tried to desolder the shield/sink but no dice. (May be doing it wrong. On the green side of the board the thick attachment joins don't give; while on the brown side there really is no solder - it seems the metal tabs are just jammed/glued in?)

However, I now noticed markings IC1 and IC2 on the brown side; and peering under the plate with a magnifying glass it does look like there may be two integrated circuit elements there (with 4 metal tab feet on each side, see new pics - sharpest I can get them). They seem to have some irregular white stuff on top, like dried paint or yogurt; from melting? or perhaps some intentional heat bridge material? I reckon that's bad news, as I imagine ICs are device-specific and can't be replaced?

So perhaps bin after all... But thanks again, a little knowledge (even if too late) soothes the mourning ;-) I may try to get the metal plate off in a more forceful way, out of curiosity.

 

[H2814D]

Don't give up yet. That plate is a heat sink and that white material you see is a heat sink compound designed to transfer heat away from the components to that plate. The components may or may not have been damaged, but getting a look at them is going to require removing that shield/plate to know for sure. Source the capacitors and replace them first. See if you get lucky with that. Like I said, they (the caps) are cheap and look like they will be easy to replace. You will only be out a couple of dollars if you do.

 

[Ommatoiulus]

This will take a little longer but I'm curious to try. Just to make sure: you do mean first replace the bigger, black capacitors, right? (Because you also mention "small surface mounted capacitors". Would these be the little block-like copper-colored bits where the Cxx markings are...?)

I watched this neat video to start actually understanding what capacitors do. Two things of note:
1) The video explains that the voltage reading between the cap's terminals should be that of the power source when it is switched on, and then gradually fall to zero when it is switched off, as the capacitor equilibrates. I'm finding exactly that for both caps (with the 'fall' taking perhaps 2 or 3 seconds.)
2) They are rated 470μF, 16V. The video seems to say that the latter means they should have withstood the 12V they were subjected to. But there may be a difference threshold for being damaged versus downright exploding...?

Thanks so much for sharing your expertise, H2814D.

 

[H2814D]

I'm glad you are willing to try. It may not solve the problem, but then again, it may. If you don't try, you will never know. At this point, it would become a challenge, if it was mine, especially with as few components as are on that entire board. And as far as my "expertise," the others here are far more the expert than I will ever be. I've learned a lot from them myself, actually, and am glad they are willing to put so much time into helping the rest of us. I just happen to have the time, patience, and money to play with electronics stuff that breaks. Sometimes I get lucky and can fix them, and sometimes I don't, but I will certainly try first. For the minimal relative cost of a lot of electronics components, compared to the replacement of whatever breaks, seems cheap to me. And I am certainly not going to ever say that Blujet's advice might not have been the best advice from the beginning.

The capacitors I am talking about are the big black ones. I can see the value on the one you said had white stuff on it and it is a 470uf 16V. If the other one is the same, then order those. They are so cheap and easy enough to find that I would probably order ten at a time, in case you decide to eventually get underneath that plate somehow and may have to do things again. Keep with the 470uF but you can go up to 25V if those are easier to find. Like I said, both of them (16V and 25V) are very common and easy to source. I don't know where you are, but in the USA the "A" seller has them anywhere from about [imath]6 to[/imath]12/13 for higher end ones for 10-20 pieces of them. Replace these first, and see if you get lucky, before trying to get under that plate. And don't use the lighter socket. If they don't work, then the plate removal would be next.

Careful work with a Dremel tool would get that plate off and then you could use a good amount of solder to put it back on later. Once you can see what is under it, you can go from there as far as determining what they are, if you can test them somehow, and if you can find replacements. Unless the part numbers are still on those chips, they would be hard to find. But like I said, I would try the caps first. Just make sure you replace them with the correct polarity. There is a positive and negative side. They absolutely MUST go back in the right way.

The smaller surface mounted caps (C18, C19, C12, C17, etc,) are visible below the plate soldered to the board. They would be a pain to locate a bad one and find replacements, since the capacitance values aren't available without a schematic or other means. I would leave those alone for now.

Good luck, and let us know if you have any questions about anything else.