Shorted voltage regulator on SMSL amp need help - diyAudio
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Old 10th May 2015, 10:03 PM   #1
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Default Shorted voltage regulator on SMSL amp need help

Hey Guys,
I have a SMSL SA60 mini amp. The problem is that the voltage regulator was shorted. While it still seems to be working it appears that other components were damaged. Before the short the voltage regulator had an input voltage of 18.37 and an output of 7.99 volts, now it has an input of 17 volts and the output is still the same; but nothing on the amp works anymore. The leds on the front don't light up, the volume doesn't work and there is no sound out of the speakers. Also since the short there is a chip on the board that gets excessively hot very quickly but I'm not sure what this chip is or what it does (It will have a red arrow pointing to it in one of the pics). The only other component on the board that even gets warm is the voltage regulator itself but it could be within its temperature range still. Any help with fixing this amp would be greatly appreciated. My understanding of circuits is not that great but I know some of the basics and have replaced blown capacitors and such before. I don't know how to test all the components but I do have a multi-meter and I can solder/de-solder components as necessary. If you have any questions or need more detailed pictures please let me know.

Also the two wires on the bottom are simply patch wires from the front aux input to the rear RCA's to give me a low level output , If you look closely you can see where the tracks connecting the RCA's to everything else were severed. This was done prior to the problem and worked fine.
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Old 11th May 2015, 04:05 PM   #2
wwenze is offline wwenze  Singapore
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Well if any voltage is dipping and the power supply is certain to be working then I would cut the power because something is shorted. Good thing the hot stuff has been identified.

What do you mean by "the voltage regulator was shorted. While it still seems to be working" - did a piece of wire go between the input and output? Did the original regulator die shorted and got replaced?

That picture does not look promising - it looks like at least one 47uF capacitor has spilled its guts everywhere, and likely most of the parts on board too. Likely beyond economical repair.
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Old 11th May 2015, 04:13 PM   #3
Binely is offline Binely  United States
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Okay since you don't have a response yet, I'll give it a go with my limited knowledge. The chip that gets hot is your pre-amplifier. The amp chip on the board under the sink is a fixed volume amp, so it has to have a pre-amp built in to change the volume. The chip in the middle is your logic board which mutes/unmutes the inputs to the amp under the sink. The sink is pretty superfluous anyway - these chips are extremely cool running because of their efficiency.

Bottom line, the board is dead unless you can confirm empirically that all the components are still okay except your chips and then replace those - but those are BIG "if"s.

The chip with the arrow to it is your signal pre-amp. It is getting hot because it probably can only handle 5-7 volts (I can't see the identifying numbers or I would know for sure.

It's hot because when you shorted the voltage regulator you overloaded it and effectively melted the traces inside it making it a very pretty looking resistor. That is all it is good for now.

Your amp chip is probably ine, it can handle up to 32 volts as long as you didn't short a pin on it.

Your logic IC if not running hot *may* be okay, but you said the LED's don't light up so I can only assume it is dead as well. It also has to be programmed so you have to assume that you won't be able to program that another dead end.

Also, it helps to know how the VR got shorted - so if you made a mistake or know how it got shorted, important to share it/own up to a mistake - we all make them. Just don't burn the building down with the hobby and I think you won't get much judging here

Chalk this one up to an oops moment - you will waste hours trying to figure this one out... but in the meantime, find an acceptable replacement and get that running before you start tearing this one apart in an effort to learn how to diagnose.

I bought a nice little amp board recently that I like very much and has similar power. You can still get a nice STA508 with a TC2000 ADC front end with 80WPC for $15us shipped through overseas suppliers. Not the same efficiency but I really like the STA508 architecture along with the Tripath front-end. For me, having an isolated ADC from the power stage makes sense in concept and I think it translates to the result.

I'll post a picture of it. This will likely run just fine on the power supply you have for the amp that broke.

Sorry to bear bad news.
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Old 11th May 2015, 04:29 PM   #4
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Thanks for the reply. Yes a piece of wire did short the input and output together and its still the original regulator. Which capacitor are you referring to? If its the one closest to the voltage regulator that looks crooked, it seems to be fine. I thought it could have been blown too, but I took it off the board and apparently there was just a poor solder connection on one leg to the board so it got bent over a little. Oh and I forgot to mention that I just spayed compressed air (upside down) onto the board in the first picture so I could find the hot components.

And as far as economical repair goes. I don't necessarily need all the features and modes to work. I planned on using it in a sort of powered speaker, so the amp volume would be set to max and input volume from the aux input would be used to control the actual speaker volume. The cost of a new one is around $80 so is there any way to get this to work as a straight forward amp? I believe it is based off the Texas Instruments TPA3116 board. At least that's what the products web page says.
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Old 11th May 2015, 04:35 PM   #5
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Quote:
Originally Posted by wwenze View Post
That picture does not look promising - it looks like at least one 47uF capacitor has spilled its guts everywhere, and likely most of the parts on board too. Likely beyond economical repair.
It more looks like ice from a coolant spray.
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Old 11th May 2015, 04:47 PM   #6
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Thanks for the replies binely and doctormord. Sorry my posts are still delayed since I'm new and I didn't see your post binely until after I replied to wwenze. And yes the shorting was my doing, stupid mistake. But I show a close up of the signal pre amp in the second pic and it doesn't seem to have any ID marking on it at all, which I assume is unusual.

Also thanks for the info about the sta508. I would really like to fix this amp because its housing fits my project almost perfectly. But if it cant be fixed I will most likely go with the sta508.

Last edited by onefierceson; 11th May 2015 at 04:51 PM. Reason: grammar mistake
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Old 11th May 2015, 06:48 PM   #7
Binely is offline Binely  United States
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Well... hard to say then exactly how to do this. You'd need to remove the sink, find your signal input trace and then short the input trace to the input line though I suspect some of those components you can see are startup-mute circuitry so it would be fiddly with startup thumps and less protected from shorts. TI has the datasheet out there for the TPA3116d2 and I've played with these amps a bit (burned out two chips - yaay!) and one thing I've learned - be careful with SMD boards. A lot less tolerant of small mistakes than through hole projects.

Also, you'd do well to cut the traces to the inputs from any other sources so you don't get unintended feedback or oscillations.

Welcome to the world of modding. It means you will break a lot of stuff, and fix some of it. Sorry it had to be this board, but in the end you will know more for it. That is funny your pre amp chip has no markings. Def some sort of multi input op-amp design though, because the TPA has it's own ADC so any PWM would just be garbage to it unless there is some mode I don't know about that it enabled through a hardware pin setting somewhere on your board.


Cheers
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Old 12th May 2015, 07:27 AM   #8
wwenze is offline wwenze  Singapore
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Desolder the regulator too.
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Old 12th May 2015, 03:11 PM   #9
Binely is offline Binely  United States
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I don't know if I would not use a regulator at all. That regulator at 18v is likely the feeder for the amp chip and the B+ will be pulling from those polycaps if not the electrolytic that I am willing to bet is fed from that regulator because they are smds and there aren't any underside traces for it.

I might replace it...
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Old 12th May 2015, 05:36 PM   #10
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Ok so I should remove the regulator so I can replace it? I can de-solder it no problem but then I tried finding a replacement I could not find one with the SF designation that mine has. Does anyone know what the significance of that marking is or where I could find a replacement?

Also this may be a stupid question but what exactly are you saying to do here?
Quote:
Originally Posted by Binely View Post
Also, you'd do well to cut the traces to the inputs from any other sources so you don't get unintended feedback or oscillations.
I assume by "cut the traces" you want me to cut the tracks (same thing as traces?) on the board similar to the way I cut the tracks from the RCAs?

And I thought I would add this picture of what's under the heat sink since it might help.
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