Shorted Voltage regulator on mini stereo amplifier

Discussion in 'The Projects Forum' started by OneFierceSon, May 5, 2015.

  1. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    Hi Guys,
    I have a S.M.S.L SA60 Mini Amp. The Problem is that the voltage regulator was shorted and I believe that it may have damaged other components on the board. Before the short the regulator had an input voltage of 18.37 volts and the output was 7.99 volts and the amp worked fine. Once The regulator was shorted the amp cut off the lights on the front and nothing works anymore. If you connect a speaker there is a quiet but noticeable humming/crackling sound that wasn't there before, even if there is no input connected to the amp. Also the board gets hot quickly around the area of the regulator but I'm not exactly sure which component is causing the heat. The regulator still has an output voltage of 7.99v but the input is around 16v. I believe that there are bad components on both sides of the regulator since the input voltage dropped 2 volts, and even though the regulator is still putting out 8v the amp doesn't work. Any help figuring out what is wrong with 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 out , If you look closely you can see where the tracks connecting the RCA's to everything else were severed. This was done previous to the problem and worked fine.

    IMG_20150505_132501.jpg IMG_20150505_132527.jpg IMG_20150505_132545.jpg IMG_20150505_132225.jpg IMG_20150505_132450.jpg IMG_20150505_132432.jpg IMG_20150505_131900_020.jpg IMG_20150505_132600.jpg IMG_20150505_131415_993.jpg IMG_20150505_132303.jpg
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    the output voltage is still 7.99 so the regulator is still working. things are getting hot because there is a high load on the regulator, something is pulling a lot of current. the input voltage went down because somethings pulling a lot of current. check other stages in the amp, probably the power output stages.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,988
    745
    get a can of freezer spray, and coat the pcb, power it up and see where it melts, start there..
     
  4. izon

    Member

    Mar 17, 2013
    163
    5
    The most likely problem is a shorted power output IC....the one with the large heat sink. Quick of other components is to wet a finger n quickly touch other parts (semiconductors) to see if they are running too hot to. keep your finger on it.
     
  5. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    Thanks for the replies. So I used the freezer spray and the only warm parts on the board are the voltage regulator and another chip that is unknown to me, I will show it in the picture below. Also I re-checked a few voltages, The voltage regulator is now getting 17 volts input and the same 7.99 volts out. The aluminum SMD capacitor just above the voltage regulator is getting 18.6 volts. So would that mean that everything up until that point is still good? Another thing is the humming/crackling from the speaker is almost unnoticeable even with my ear next to it. Everything else is still non-functioning though.

    Alfacliff how would I go about locating/checking the power output stages of the amp?

    IMG_20150505_190423_904-1.jpg
     
  6. Denesius

    Member

    Feb 5, 2014
    89
    14
    How good are you with unsoldering/resoldering SMD devices? That chip should not be getting that hot, but without part numbers or schematics, it's hard to say what's going on. If the heat sink is not warming up, you're probably looking at a pre-amp or a driver that's burned out. The 'hum' is power supply noise (caused by the excess current draw) that's getting into the speaker. From the description your regulator chip is ok, the problem is downline.
     
  7. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    I've soldered plenty before but never something as small as the chip I pointed to above, But I can give it a try if you think it could be the problem. I should be able to remove anything else on the board relatively easy.
     
  8. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    OK so once I remove the above chip from the board what am I looking for? Will it have ID numbers on the bottom?
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,988
    745
    the chip should have numbers or letters on the top surface ...
     
  10. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    That's what I thought, but there doesn't appear to be any numbers or letters on it at all.

    IMG_20150508_133412_259-1.jpg
     
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,988
    745
    looks like the manufacturer has erased it, to stop copying, unless you can get hold of a circuit diagram or another board to compare with.
     
  12. OneFierceSon

    Thread Starter New Member

    May 5, 2015
    8
    0
    Well I don't have another to compare to and I couldn't find any diagrams or parts lists. On the products web page it says that it is based off a Texas Instruments TPA3116 board, although I don't see much resemblance between the two. Is there any other way to get this amp working? Bypass the aforementioned chip maybe?

    Link to products webpage http://www.amazon.com/SMSL-SA-60-60...UTF8&qid=1431139232&sr=8-1&keywords=smsl+sa60
     
Loading...