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Amplifier transformer broke?

Discussion in 'Electronic Repair' started by [email protected], Jun 5, 2006.

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  1. Guest

    I have a 12 month old amplifier called Prosound, a Taiwanese
    manufacturer, which has stopped outputting audio.

    The electronic display appears to be fully functional, which is powered
    by one main transformer. There are 3 main leads coming from it,
    yellow/green, black, and the display power. The display power is
    obviously working, the yellow/green is out putting 30V and 60V, however
    the black lead is not reading anything.

    Question. Could a transformer blow if it still outputs various other
    voltages? If not, what else could it be? I've checked the fuses and
    they're still ok.

    Help appreciated.

    Darren
     
  2. jakdedert

    jakdedert Guest

    Yes, but probably not in your case. You've measured 30 and 60 volts
    referenced to what? If there are only three wires coming out of the
    transformer, it would probably be a center-tapped 60 volt unit...giving
    you 30 volts on either side of the black lead. Try measuring from black
    to yellow, then black to green. I would bet that you will get 30 volts
    each time, and that yellow to green is where you measured 60 volts.
    That's entirely normal.

    Why have you fixated on the transformer as the source of your trouble?
    Most likely it lies elsewhere....

    jak
     
  3. Guest

    Thanks Jak,

    Sorry for my misleading description, there are 3 sets of wire.

    1. Black/black - Motherboard
    2. Yellow/yellow/green/green - Motherboard
    3. Mixure - Front display.

    We know cable 3 works due to the front display is operational, cable 2
    is outputing both 30 and 60 volts, but I cant get a AC or DC voltage
    out of cable 1. Obviously in AC, but it was worth a try.

    I know very little about electronics, but I am able to visually see
    there are no blown caps, no burnt out transisters, and the 4 fuses are
    in tact.

    The display doesn't read any graph of sound input, so I would guess
    that the output side of it still works. However, I really don't know
    what this means :)

    I can hear a slight humming noise, but that could be normal for a big
    transformer, I guess.

    Any more advise Jak or anyone else? :)
     
  4. jakdedert

    jakdedert Guest

    Still pretty vague. '3 sets' is confusing. For instance, set #1:
    'Black/black'. Is that two wires, both black etc?
    Still don't know where you are measuring, from each wire to ground, or
    from wire to wire...and how many wires are there? Four; two yellow and
    two green?
    Visual cues only go so far. A component can be bad with no visual
    indication.
    There is no 'output side' of a display, unless you count light output.

    I'm guessing this is probably beyond your experience level to even get a
    start at fixing it; but if someone wants to chime in, I'm glad to be wrong.

    Good luck.

    jak
     
  5. Arfa Daily

    Arfa Daily Guest

    I agree with jak that it is highly unlikely to be a transformer problem. It
    is rare for individual windings to fail on the secondary side. It would help
    to know what the two black wires are connected to. For instance, the AC - AC
    input of a bridge via one of the fuses ? If this were the case, then at
    least you would know that there should be some kind of winding between the
    two blacks, and you could easily measure across them with an ohm meter.
    However, I tend to agree that blacks would usually, by convention, be
    winding centre taps, so this is in fact what they might be, and both
    connected to ground, hence the reason that you get no AC reading across
    them.

    Is there no indication on the transformer as to what windings and output
    voltages it has ? Transformers often have this information on them,
    particularly when they have permanently fixed colour coded wires.

    Beyond this, I am of the same opinion as jak, that a diagnosis and repair of
    this type, is probably beyond a beginner with no electronic service
    experience. Good news is that if nothing is burning up, and all fuses remain
    intact, then the problem is likely not too serious - assuming that it's
    actually not the tranny, of course ...

    Arfa
     
  6. g. beat

    g. beat Guest

    Technical schools and many high vocations schools take in local community
    projects such as yours.
    Check locally - and do not hand this unit to a "student want-a-be" - I have
    seen repairable gear destroyed by that process.

    This is one of those areas where experience and skill together make the best
    technicians and repairman. Many are retiring!!

    g. beat
     
  7. James Sweet

    James Sweet Guest


    My guess would be the output transistors are blown, along with likely
    other parts in the chain. This would cause most amps to shut down and
    behave similarly. If you know little about electronics then either junk
    it or have it serviced, you won't get anywhere without some propper
    tools and knowledge.
     
  8. Tom Hotaling

    Tom Hotaling Guest

    Yes all the other comments do apply and the repair scene is getting
    very sketchy these days. For a lot of newer eqp the manufacturers won't
    or can't supply any documentation. The comment about the older techs
    just knowing where to start is very much to the point. Unfortunatly
    there are repair shops that take things in, charge an estimate fee and
    then say they can't fix it. "tis a sad state of affairs lads"
    All that being said:
    1. the black wires, just 2? may be the 110 AC input power. You didn't
    mention any other wires, are there any others?
    1.5 just because you measure voltage is not a lot of help. The power
    supply section could be bad, rectifiers, regulators, etc.
    2. most modern amplifiers have a relay to disconnect the speakers from
    the output. This allows turn on with out a 'thump' and there's usually a
    circuit that will sense DC on the output and disconnect the speakers to
    prevent damage. There are a couple of chips designed specifically for
    this function and they can be troublesome and crap out by them selves.
    3. If your finals are blown or partially bad, based on your stated low
    level of knowledge about electronics, it's probably beyond your
    expertise to repair.

    I would seek out a repair shop that specializes in audio. NOT your
    neighborhood TV shop, which are just about nonexistent these days
    anyway. Look around the web, there are several that advertise. Be wary
    of repair shops attached to the "big box" or even small box stores. Be
    prepared to have to ship, and pay for it, pay an estimate fee up front,
    and a substantial repair fee, and all this must be balanced against your
    original purchase price or the replacement cost. A lot of stuff gets
    thrown away or "abandoned" because of cost issues.
    "a sad state of affairs indeed"

    I could offer a couple of other things to check, but if you can't make
    the repair, can you solder? what's the point. Perhaps the only advantage
    would be having a reasonably good idea of what's wrong, to know whether
    the repair shop is padding the bill.

    good luck

    tomh
     
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