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Help with portable speaker system | Fried circuit board

Discussion in 'General Electronics Discussion' started by xxkellerman, May 2, 2014.

  1. xxkellerman

    xxkellerman

    4
    0
    May 2, 2014
    So i wanted to make a portable speaker sistem and i succeded.
    It was a subwoofer with an integrated amplifier.
    I just cut out the 220-240V~ Transformator and connected a 12V 60Ah battery to it. Everything was fine, it played like it was hooked on electricity.
    But then i forgot to isolate a 12V cable and it touched some elements on the circuit board. It doesnt play now and i dont know witch elements are fried and how to fix it. I dont know much about electronics or circuits and it would probably cost 40$+ to get this fixed by someone. If anyone has solutions of guides how should i atempt to fix this i would be greatfull. Because they dont make alot of good speakers with integrated amp and subwoofer, and i dont want to spend 100$+ on a new one.

    Thanks! Pictures below.

    The front (i drilled a hole for the 12V cables):
    [​IMG]
    The back:
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    [​IMG]
    Sorry for some bad pic quality but i hope you can see everything.
    If not i will make some new ones.
     
  2. xxkellerman

    xxkellerman

    4
    0
    May 2, 2014
    BUMP
     
  3. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    Hi and welcome to Electronics Point :)

    So you let the positive supply from a 12V battery touch some components on the board?

    Most likely you will have fried (that's the technical term for it) at least one of the semiconductor components on the board, possibly all four. These semiconductors are
    • One black plastic IC with two rows of four pins, slightly towards the back of the centre of the board,
    • Three black plastic ICs along the front of the board, which are screwed into the front panel for heatsinking.
    Can you post the markings on those devices and we can suggest how to test them.

    But there are more serious problems here. The board will not work very well from a single 12V battery. I'm pretty sure it has a "split supply" arrangement and was powered from a centre-tapped transformer - there would have been three wires from the original transformer, right? Also, both of the supply rails would have been more than 12V - the smoothing capacitors (the big cylindrical brown things) are rated for 25V each. So even if you replace the ICs, the board will not work well from a single 12V battery. Probable problems will be high distortion and low power output.

    So I really don't think that board will do what you want. If you want a portable amplifier that runs from 12V your best option would be an automotive amp.
     
  4. xxkellerman

    xxkellerman

    4
    0
    May 2, 2014
    Thank you for your explanation.
    I have made some shots of the board and transformer LINK: http://imgur.com/a/IuqJj#0
    My friend has experience in soldering and he sead he could help me out.
    So the thing to do is to replace those 4 semiconductors?

    as for the "powering it" part.
    Is it possible to use a 12V battery for split supply (Yes the transformer has 3 cables going to the board, it also states 12Vx2 on the top of it, provided in link above) or do i have to buy a 24V battery?
    And when it was hooked to the 12V battery it rather played nicely, loud and i heard no distortion (Could have been because the speaker head only 20W).But the subwoofer played nicely too.
     
  5. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,266
    Nov 28, 2011
    I'm surprised that you say it sounds OK when powered from a single 12V battery. If you want to power it properly, you need two separate batteries - one for the negative supply rail and one for the positive. But each one should be more than 12V if you want maximum power output. The TDA2030A is rated for 44V maximum total power supply voltage, i.e. ±22V. With the original 12VACx2 transformer, the rails would have been around ±18V or thereabouts. With two 12V batteries, i.e. ±12V supplies, a single TDA2030A can produce about 10W into a 4 ohm speaker or 6W into an 8 ohm speaker. If that's enough for you, then two 12V batteries will work OK.

    Yes, I would start by replacing those four semiconductors. That may not be all that's damaged though. Also you should remove the four diodes where the battery connects. You can (and should) connect the batteries directly across those two large electrolytics. One battery across each one, observing the polarity marked on the electrolytics. This will mean that the positive side of one battery will be connected to the negative side of the other battery at the "0V" rail point, which also connects to the outer screens of the input connectors. If you want to switch the batteries ON and OFF (which I recommend), you need to switch the other two wires. You need a DPST switch (or DPDT, with two terminals unused).

    If your batteries are rated for 60 Ah they will be able to deliver an extremely high current if shorted. This risks not only damage, but burn injuries! You need to be VERY careful with the wiring from them, and the board when it's powered up from them. Use thick information that cannot come off. I also recommend adding fuses as close as possible to the battery, on the two wires that go to the switch (but not the 0V connection to the commoned-up terminals). You can use glass fuses rated at a few amps, or PTC resettable fuses such as http://www.digikey.com/product-detail/en/RUEF250/RUEF250-ND/1045776 or http://www.digikey.com/product-detail/en/SRP200F/SRP200F-ND/721796.

    I can identify the 8-pin IC as a 4558 made by STMicroelectronics, and the left and middle devices on the front as TDA2030A. I can't read the marking on the third one.

    The 4558 can be replaced by any of these (around USD 1~2):
    STMicroelectronics MC4558CN: http://www.digikey.com/product-detail/en/MC4558CN/497-1960-5-ND/599556
    STMicroelectronics TJM4558CN: http://www.digikey.com/product-detail/en/TJM4558CN/497-7654-5-ND/1039908
    Texas Instruments RC4558P: http://www.digikey.com/product-detail/en/RC4558P/296-1414-5-ND/277060
    NJR NJM4558D: http://www.digikey.com/product-detail/en/NJM4558D/NJM4558D-ND/673768
    Fairchild KA4558: http://www.digikey.com/product-detail/en/KA4558/KA4558-ND/1050637
    Rohm BA4558: http://www.digikey.com/product-detail/en/BA4558/BA4558-ND/658330

    The TDA2030A was originally made by STMicro and is second-sourced by Unisonic Technologies Co Ltd (UTC). It appears to be available from Jameco at http://www.jameco.com/1/1/35025-tda2030av-tda2030a-18w-1-channel-hi-fi-amplifier-35w-driver.html. Price is around USD 2 each.
    Check that the third IC on the heatsink is also a TDA2030A.
     
  6. xxkellerman

    xxkellerman

    4
    0
    May 2, 2014
    Thank you for all the help you provided, i guess i have quite a bit of work ahead of me.
     
    Last edited: May 4, 2014
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