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Loose solder joints

Discussion in 'Shock Brother's DIY Amps' started by inspectorted, Sep 14, 2010.

  1. inspectorted

    inspectorted TDPRI Member

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    I need some amp guys to chime in... I typically build guitars, so when it comes to amps I'm lost. I have a crate gxt100 sitting around I need to sell. The problem with it is if you wiggle the input jack while it's on channel A it pops and cracks through the speaker, but if you change to the B channel with the same input jack it's just fine. If this is a loose solder joint, how do you find loose joints?
     
  2. muchxs

    muchxs Doctor of Teleocity

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    It's a circuit board amp so there's probably a PC mounted jack. Those break all the time, nature of the beast. With any luck you can get at the back side of the board and re-flow the joints. Without any luck? They call that "SOL".

    You might want to think about bench time versus resale value unless your time is free.
     
  3. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Is Channel A the dirty and Channel B the clean channel?

    You may not be hearing the crackle as badly in Channel B if it is lower gain. As far as fixing the jack, it might be easy (open amp, resolder, done) or it might be hard (it might be hard to get to the circuit board, there might be a break in the board or jack, etc). You'll have to take a look at the jack's wiring inside.
     
  4. Ronsonic

    Ronsonic Tele-Afflicted

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    I'm betting that it is a bad solder joint, just not at the input jack. Crates are typically full of feeble solder joints and it's likely that the bad joint in this case is on the volume or a tone pot in the channel closest to that input jack. The joint is bad enough that flexing the circuit board by annoying the jack is enough to upset it.
     
  5. inspectorted

    inspectorted TDPRI Member

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    This sounds pretty close as to whats going on... Channel A is the clean side. This is the channel I'm getting the noise from. Also when in this channel if I mess with the gain it cracks and pops like wiggling the input jack. The gain is right next to the input jack. I've had the board completely out but I don't know how to find or identify a loose solder joint.
     
  6. inspectorted

    inspectorted TDPRI Member

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    Whats the best way to find a loose solder joint
     
  7. Ronsonic

    Ronsonic Tele-Afflicted

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    Couple of ways. First is to examine the solder joint closely look for a ring around the lead or post. Wiggle the part that is supposed to be soldered in while looking at the other side of the board if the lead is moving then the joint is bad.

    The easiest way is to look at the front panel and if it says "Crate" then figure everything bigger than a 1/2 watt resistor. No exaggeration bro.

    Wave soldering, the process used in mass production is especially weak on large components which soak up a lot of heat and components near the edge of the board. Jacks and control pots are the worst since they're both large and on the edge. And Crate sends these guys down the line fast.

    My bench time is expensive and for those amps it is much more cost effective to just hit all the pots, all the jacks and check the large filter caps and transistors.

    Lay a wetted tip on the joint, watch the solder melt as you feed in a little fresh, give it a second or two to soak then go to the next joint. Seriously hit the whole front panel, check the rest and be done. If you suspect it, solder it. It's faster to solder than to wonder whether you should or not, surer, too.
     
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