Help with speaker circuit assembly

Discussion in 'Electronics & Electrics' started by joomax, Jan 8, 2019.

  1. joomax

    joomax Member

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    Hey everyone, first time posting in this section! crazy broad forum we've got here.

    Over the holidays I transplanted a really old hifi system into a big suitcase I found. I've done this before with little pc speakers and both have worked well without really needing much electronics knowledge. For this one I was going to mod it to run from battery power, but there's no step down transformer in the unit to make soldering in a battery simple, so I gave up on that haha so it just runs from AC power - easy!

    All is well except for one problem which has stumped me. The circuit that was inside the amp unit has this weird right-angled connection via 4 multiple-pinned connectors to join up the front panel of the unit with the rest of it. The front panel is required to be connected for the whole circuit to be powered.

    Thing is, whenever I move the suitcase around, something weird goes on with the connection. Turning the unit on will result in a really loud buzzing in the speakers, and if left for too long they speakers themselves start popping out of control. I am regularly able to remedy this by just wiggling the front panel part around and sometimes just reconnecting it altogether. Seems like a certain orientation has to be met for it to work properly.

    Here's a picture. Any ideas on what I could do? Thought about sanding down the pins and maybe putting some isopropyl around the place, but thought I'd ask here first.

    [​IMG]
     
  2. Technics

    Technics Member

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    I wouldn't sand the pins as you are likely to remove any plating on them. The plating is usually there to resist oxidation. It's often quite thin and exposing the metal below it will sometimes temporarily fix the problem but often it leads to the subsequent rapid failure of the contact. A pencil eraser is usually aggressive enough to remove oxidation without taking off the plating completely. There are also some specialised cleaners like DeoxIT specifically for removing oxidation but they are pretty expensive for what you get. The isopropyl alcohol should be fine for cleaning after the eraser.

    Looking at the setup, the biggest problem seems to be the removal of the mechanical support and grounding that was provided by the original hifi case. A lot of the original support for the boards is no longer there so they can flex relative to each other. This can break solder joints as well as damage the connectors. Particularly with the lower costs boards made from phenolic resin which are unable to resist flexing as well as higher quality materials. There looks to be a point on the top PCB (right near the volume control PCB) where it was designed to connect to a metal panel via a screw. Hopefully the continuity of the ground between PCBs is not reliant on this external (now removed) metal work.
     
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    joomax

    joomax Member

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    hah, yeah i thought it might have been a bad idea to ditch the original casing entirely. Thought I'd be able to mount it well enough inside but it's a bit of a mess. Might have a look at re-orienting the entire thing the other way around.

    Can I reintroduce some metal and connect it to that pin to act as ground?
     
  4. Technics

    Technics Member

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    It would only be strictly necessary if it was used to bond the ground across several boards. if there are similar metal tabs on other boards then it may be worth soldering or bolting a wire connection between them. It may simply have been to bond a metal shield to ground in which case I wouldn't do anything unless you have noise issues.

    I think the issue you have described is probably down to the poor mechanical support causing bad connections.
     
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    joomax

    joomax Member

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    Okay yeah, makes sense. It works fine when it's connected properly, so I'll have to look at fixing up some supports.

    Thanks for the insight ! :)
     

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