Repairing Blown Circuit - Overpowered with 10v 2.4amp instead of 5v 2amp

[Bryn]

Hello,

I know near nothing about circuits and am happy to learn what I need, to get this repaired. Where do I start?

I have a bluetooth music receiver with digital out (toslink coax) purchased from overseas. I connected an incorrect power supply and it no longer works
(I first connected the correct power supply and it worked fine - don't ask...). The receiver no longer powers on or shows any life what
so ever. Link to photos of receiver and circuit below:
https://goo.gl/photos/67HMQDKBLuaTQZ3F6

The only tools I have are a soldering iron and amateur multi-meter.

Thanks in advance!

 

[cowboybob]

Welcome to ETO, Bryn!

I'd start here:

With the PCB disconnected from everything, measure the resistance across the two points indicated by the red arrows (measurement 1), then reverse the leads and measure it again (measurement 2). I'm taking a guess that the white component is a diode meant to protect against reverse current (what you did) and we're trying to assess its condition.

Let us know what the two measurements were.

 

[audioguru]

We do not know if the amateur multi-meter shows anything when it measures the resistance of a good diode. My multi-meter has only 0.2V when it measures resistance so a diode does not conduct and the "diode-test" function must be used instead.

 

[cowboybob]

We do not know if the amateur multi-meter shows anything when it measures the resistance of a good diode...

Exactly. That's why I suggested what I did. Two tests going on here: 1. Does the OP know how to use the multimeter. 2. If he does, what does it show.

Tad ridiculous to assume his multimeter is the same as yours. If nothing else, if it measures infinity both ways, there's a clue.

 

[audioguru]

My expensive Fluke multimeter uses a voltage of only 0.2V to measure Ohms without causing a good silicon diode or transistor to conduct. I think a cheap Chinese copy is the same but its switches and display will fail soon. Then the diode will measure infinity both ways and should be replaced but the product still will not work.

The multimeter should be used to measure the adapter voltage and the output of the diode voltage when the product is powered. We bet the adapter voltage is fine but the output of the blown diode is zero. If the diode is shorted then its voltage drop will be much less than 0.7V.

 

[Les Jones]

I suspect the white SMD may be a fuse rather than a diode. If that is the case then it would not matter about the test voltage on the resistance range of the multimeter. I think AG's suggestion of measuring the voltage on both sides of the device is the most reliable. I have seen some products where the reverse polarity protection is a series fuse and a shunt diode that is capable of carrying the current required to blow the fuse.

Les.

 

[alec_t]

The cause of the failure was over-voltage, not reverse voltage. It is likely that if a fuse is present it (and probably other components) will have died.

 

[cowboybob]

We don't know jack about what he did. Nor do we know jack about his level of expertise.

Telling me I'm wrong about an extremely simple test (as stated) isn't helping the OP one iota and it's annoying me. It it a definitive test? No, of course not, but it would tell us reams about the OP's expertise and much else about a circuit we ALSO don't know jack about. It's all utter speculation at the moment.

My expensive Fluke multimeter uses a voltage of only 0.2V to measure Ohms without causing a good silicon diode or transistor to conduct

Big whoop. That's theory, NOT practice, my friend. My cheapest DVM, using the Ohms scale and the method I gave the OP, very reliably gives me an indication of a diode either being shorted (0Ω both ways), open (∞Ω both ways) or at least acting like a diode (HighΩ one way, LowerΩ the other). The rest of my devices do the same, even a ancient analog metered one.

I've used this technique since I was a kid.

 

[Nigel Goodwin]

The rest of my devices do the same, even a ancient analog metered one.

I've used this technique since I was a kid.

Analogue meters (at least non-electronic ones) have always tested diodes fine, but most digital ones don't on the ohms ranges, because (as AG said) they deliberately don't out out enough voltage to make a semiconductor junction conduct. This is so you can better test resistors in-circuit, and because of this they have special 'diode test' ranges that do output enough voltage, and also measure the actual junction voltage rather than ohms.

 

[cowboybob]

Nigel, I understand all that. But, again, I would argue that it's arcane minutia about multimeters that would be lost on a newb with unknown capabilities.

And it also suggests to the OP that my procedure (which works well enough given the task, as defined) is without value or merit because it's inaccurate, which demonstrably it is not.

Someone asks for the time and instead gets a lecture on how a watch works doesn't strike me as having listened to the question... .

 

[audioguru]

Why argue about testing the resistance of a white thing when we need to know if the circuit is receiving the proper voltage? The white thing in series with the power input jack might be a blown fuse or a blown or shorted diode. Maybe the circuit will work if the white thing is simply jumpered with a wire?

 

[Mickster]

I'd though about the white thing being a fuse yesterday, but when looking at the other pics in the OP's 1st post, they can be found in a number of different places on the
PCB. What's the possibility of them all being fuses and separating different sections of the whole circuit?

EDIT:
The cap directly behind the input socket looks like it may have vented too.

 

[alec_t]

We don't know jack about what he did.

Doesn't the thread title give a clue? Admittedly, we may not have the whole story.

 

[cowboybob]

edit

 

[cowboybob]

Doesn't the thread title give a clue? Admittedly, we may not have the whole story.

My emphasis.
Exactly. And what if it were not only over voltage but reverse polarity as well? And there's still the OP's unknown level of expertise. The mistake was made. Why would we suggest that he (might) do it again.

Why argue about testing the resistance of a white thing when we need to know if the circuit is receiving the proper voltage? ...?

Note:

... The receiver no longer powers on or shows any life what
so ever.

Presumably the OP used the correct PS to make this observation. "Proper voltage" is not an issue at this point.

I'd though about the white thing being a fuse yesterday, but when looking at the other pics in the OP's 1st post, they can be found in a number of different places on the PCB. What's the possibility of them all being fuses and separating different sections of the whole circuit?

EDIT:
The cap directly behind the input socket looks like it may have vented too.

All valid points, Mickster.

Bryn, are you still out there?

 

[Mickster]

OP has a similar thread over at AAC:
https://forum.allaboutcircuits.com/...ed-with-10v-2-4amp-instead-of-5v-2amp.120164/

My guess is that this is not a high priority and there doesn't appear to be a schematic to fit the information provided, so until we get more info from the OP regarding simple tests which have been suggested, further input is just going to be speculative.

My 0.02c

 

[cowboybob]

I agree, Mickster.

Went to ACC. Similar advice. Looks like the OP's going to chuck it.