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Home hifi ampli fixing problem

Discussion in 'Repairing Electronics' started by Zeno, Jul 17, 2016.

  1. Zeno

    Zeno New Member

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    Hi all! I'm from Italy.
    I'm trying to fix an old ampli wich was used with a record player.
    It is not broken, because when plugged it sounds. But it doesn't sound very well.
    When i turn it off for the time that remains on, it sounds very well.
    I thought that it may be a capacitor or a power section problem but i don't know where to start to test it.
    It doesn't seems to have any sign of broken components in a first sight.
    Do you know what can be the problem? Which components may i have to test if are properly working?
    Thanks for your time.
    Greetings,
    Francesco.
     
  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Hi Francesco,

    You don't repair things by testing components, you need to fault find the entire circuit.

    First thing, you don't give any details on the item at all - a schematic would be best, make and model would help, and even a picture of the board would give us somewhere to start.
     
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  3. Tony Stewart

    Tony Stewart Well-Known Member Most Helpful Member

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    power supplies with bridge rectifiers only pump current for a short time to keep the voltage up between peaks. If the capacitor has low dissipation factor, the voltage will integrate up and sag down with a skewed triangle wave at twice the line frequency with a few harmonics. But if the big caps dry out and develop a high series resistance, the pumped current adds a stepped pulse which contains a lot more the harmonics like a buzz instead of a hum. So replace all the big old electrolytic caps is a good practise.
     
  4. dave

    Dave New Member

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  5. Mark G. Cooper Sr.

    Mark G. Cooper Sr. New Member

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    If this record player amplifier is old, I would highly recommend replacing any electrolytic filter capacitors, which are part of the power supply circuit. Whenever repairing old audio equipment, that is a very good rule of thumb since over time they dry out and become 'leaky' and will cause distortion to the sound or you may not hear anything at all except a 'humming' sound.. Good luck ! Let me know if I can offer any further assistance.. Mark..
     

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