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Just a quickie (pardon the phrase). Todays challenge from FBT.

Discussion in 'Amp Tech Center' started by Jon Snell, Oct 22, 2020.

  1. Jon Snell

    Jon Snell Tele-Holic

    Aug 31, 2015
    Jurassic Coast. UK.
    This digital amplifier tried to set fire to the stage!
    FBT Amico with skid marks!
    Screenshot 2020-10-22 at 19.32.01.png
    I am a valve specialist but worked on digital, FM and analogue for many years. So, I said I would take a look.
    A look I did and decided that the 12volt IR2110 supply had gone to possitive rail, some 65volts north of what it should be, taking out the extremely low ESR Dipped Tantalum Bead capacitors, the zenor diode and the two IR2110s. Luckily the output MosFets were OK as the chips died first.
    The culprit; Screenshot 2020-10-22 at 19.31.21.png
    An innocent looking LM317 after the voltage drop circuit.

    The Capacitors definately have had a party and been left with either no heads or at the very least a nasty hangover.

    I replaced the 5 capacitors, zenor diode, dropping circuit and IR2110s, then took a look at the driver board;
    Oh dear skidmark city! Screenshot 2020-10-22 at 19.31.02.png

    So after a while with the best cleaning solvent in the world, Tricoethylene, HOCH2CH2OCH2CH2OCH2CH2OH to all the boffins or Tric to us oldies, it cleaned up a treat.

    Time to power it up. So expecting it to take a photograph of me and explode again, I switched on.
    No smoke, no flames ... what the ?
    Added a loudspeaker after checking for zero DC on the speaker output and yes, it works.

    A very happy customer.
    Just goes to show that whatever the problem is, with a lot of thought, plenty of experience and a hot soldering iron with access to spares, anyone can fix anything.
    BobbyZ likes this.
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