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  1. #1
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    Dirty circuit board causing failure

    This is a wired controller for my computer audio system.

    It stopped working. It uses a soldered on switch and green indicator led light.

    It had a lot of white material around the solder points. I cleaned it with contact cleaner and warm soapy water.

    And GENTLY scraped away the corrosion using a jewelers screw driver.

    I do not know what else to check. I has a very nice base speaker along with left and right ones.

    If I have to, I can salvage parts from much of it. Like magnets, wire, etc.

    Click image for larger version. 

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    Re: Dirty circuit board causing failure

    Warm soapy water is probably the worst thing you could have used, it dissolves the lubricants in the controls and probably introduces new corrosion.

    Please show us the other side as well, we all know what solder joints look like. My best guess is this is a purely passive device and the problem lies elsewhere but you haven't told us what the board does or what audio system it is from.

    Brian.
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    Re: Dirty circuit board causing failure

    Board is from a Logitech speaker system for a computer. It controls the volume.

    I did not bath it in soaper water, Wiped it with a paper towel.

    Click image for larger version. 

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    Re: Dirty circuit board causing failure

    All that board holds is a volume control, a switch, an LED and an input jack socket. The switch sends a power signal back to the speakers and also turns the LED on or off.

    If it has stopped working completely, the only possible faulty part can be the switch. Does the LED turn on and of when you press the switch?

    Brian.
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    Re: Dirty circuit board causing failure

    The led does not light up any more.

    I have one of these.

    https://www.amazon.com/TXINLEI-898D-...gateway&sr=8-3

    But do not know how to use the hot air rework as it came with little instructions.



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    Re: Dirty circuit board causing failure

    You only use hot air for soldering/unsoldering surface mount components (SMD) but all the parts on that board are "through hole" so conventional soldering methods are used.

    I strongly suspect your problem isn't on the board at all but in the amplifier or the cable. The LED just comes on when the switch is pressed but it is a dual-gang switch (two identical switches sharing one press mechanism) and the chances of both gangs failing simultaneously is very, very low.

    If in doubt, remove the switch from the board and using the photograph in post #1, link the top middle and top left pads. then link the bottom middle and bottom left pads. If the switch was faulty the LED will be on and the amplifier working normally.

    Brian.
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    Re: Dirty circuit board causing failure

    Ok, thanks a lot.

    Do I use the desoldering wick or my desoldering gun?

    What would be a good temp to set my iron to?

    - - - Updated - - -

    THis is what I have after removing switch.

    Is what is circled, the ones I put a jumper across?

    Click image for larger version. 

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    Re: Dirty circuit board causing failure

    Desoldering wick is probably the best thing to use for that kind of component.
    The best temperature depends on the kind of solder you use. The older type which was made of lead and tin is best around 250-270C but the lead free types tend to need a little more heat, I usually aim for 280-300C.
    Yes, the circled points are correct, basically the switch would short those points in the 'on' position and would short the middle and the other pin in the 'off' position. Linking them will make it 'always on'.

    The switches are very inexpensive if you want to fit a new one.

    Brian.
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    Re: Dirty circuit board causing failure

    Quote Originally Posted by betwixt View Post
    Desoldering wick is probably the best thing to use for that kind of component.
    The best temperature depends on the kind of solder you use. The older type which was made of lead and tin is best around 250-270C but the lead free types tend to need a little more heat, I usually aim for 280-300C.
    Yes, the circled points are correct, basically the switch would short those points in the 'on' position and would short the middle and the other pin in the 'off' position. Linking them will make it 'always on'.

    The switches are very inexpensive if you want to fit a new one.

    Brian.
    I soldered 2 pieces of hookup wire between those points.

    In the process, 2 of those "copper connections" in the solder holes came loose.

    My eyes are not what they used to be even using a magnifying glass and a very fine tip on my iron.

    But, the sound controller did make a popping sound in the subwoofer when it was plugged in.

    The led light did not come on.

    I think the switch is bad.

    What do you think?
    There may be a "solder bridge" that I can not see between 2 spots.

    There is not much space between the solder points.

    Is there a plan B?

    - - - Updated - - -

    Quote Originally Posted by betwixt View Post
    Desoldering wick is probably the best thing to use for that kind of component.
    The best temperature depends on the kind of solder you use. The older type which was made of lead and tin is best around 250-270C but the lead free types tend to need a little more heat, I usually aim for 280-300C.
    Yes, the circled points are correct, basically the switch would short those points in the 'on' position and would short the middle and the other pin in the 'off' position. Linking them will make it 'always on'.

    The switches are very inexpensive if you want to fit a new one.

    Brian.
    Thanks Brian. I got it working.

    I gently scraped away some brownish residue and tried it again with success.

    As I have that plugged into a power strip (along with my other computer items), I really do not need that switch as I always leave the switch in the on position.

    I may at some point go back and add the switch.

    Some of the things I learned:

    1. Use the narrowest tip when solder joints are close together

    2. Do not forgot to tin the tip before each use

    3. When changing tips, place original tip away from where your hand or finger can touch it

    4. Some I forgot to list



  10. #10
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    Re: Dirty circuit board causing failure

    I think we all know point 3 from personal experience

    Well done for getting it going. If you want to replace the switch, keep the original for reference and search for a similar one. It should be a switch with 6 pins and watch out for the length of the push bit. They are made in two basic body sizes, I think yours is the smaller one, the other is about twice the size. The push protrusion is made in various lengths for different purposes but almost all equipment uses the same size. You need a latching type, the momentary ones only operate for as long as you keep pressure on them.

    Example (but check the size): https://www.ebay.com/itm/8-5-x-8-5mm...wAAOxye3BRyEOc

    As you mangled the solder pads, if you fit a new switch, use fine insulated wires to bridge the pins to the nearest solder joint on the same track or carefully scrape away the green solder resist paint to expose the copper track underneath it and attach the wire there. Basically, all you need to do is joint across the original route of the track, the exact layout of the bridge isn't important.

    Brian.
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    Re: Dirty circuit board causing failure

    Thanks.

    Does it help to fan out th braided solder wick a little?

    I had 2 kinds of roughly the same diameter.

    One absorbed better than the other.



  12. #12
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    Re: Dirty circuit board causing failure

    No, the braid removes the solder by capillary action. The fine spacing between the wires in the braid causes a meniscus to form in the gaps and it's that that draws the solder into it. If you splay the wires, the wicking action stops and you just get a solder joint forming.

    The other factor that decides how well it works is the kind of flux impregnated into it. Copper easily oxidizes and solder will not stick to copper oxide, the flux is activated by the heat and it breaks down the oxide layer so the solder sticks to the wires in the braid.

    Brian.
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