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Technical Help ??

Discussion in 'AV Receivers & Amplifiers' started by coxy, Jan 28, 2003.

  1. coxy

    coxy
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    My amplifier has identified a short circuit on one of my biwired mission 735i speakers. The cable I've been using is 4 year old QED Qudos Micro 4-core and I am sure it is the cable that is the problem by process of elimination. Can anybody help with the following:-

    1. How do I identify where in the 4 metres of cable the shorting is taking place?

    2. What would be a good replacement biwire cable. I am now using a new Yamaha DSP630 amplifier after the short circuit blew up my Sony STRDB925 so I'm a bit short on cash!

    3. Now I know what caused the Sony amp to blow up where can I get it fixed cheaply?

    4. Has anybody else had problems with this cable?

    thanks in anticipation!!!
     
  2. Jase

    Jase
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    Are you sure the short is located in the actual cable and not at the binding post? It only takes a stray bit of wire to touch the casing and it will short out. Using banana plugs can avoid this if the amp will accept them.

    For other cables have a look at www.hificables.co.uk

    Might be worth taking the sony amp to your local Sony Centre to see if they can repair it. Most amps have protection circuits and will shut down if there is a short so are you absolutely sure the cable caused that amp to blow up??
     
  3. cribeiro

    cribeiro
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    Well, I am not a technician, but I have an idea: take a voltimeter (if you want a house-made tester, use a battery and a little lamp) and a cable you know is working. Then, with a very little pin (check first with the tester if it conducts electricity) you may use that circuit including more and more of the damaged cable on each step. Stick one of the ends of the tester to one end of the damaged cable, and the other end of the tester, with the pin, you go pinning each 1 meter, for example. That will tell you in which section it is damaged, but I don't know if that will actually cause more damage.
    I am sure that there are some kind of scanners you can do, but I guess that will cost more than the cable itself!
    If you replace the cable, look for the same. If you don't find it, find one with the same gauge (that means, cross section, or area of the cable if you look at a perpendicular cut, or easily, the specification that should be written all along it). If it is any special aleation, take care of that also.
    As far as I know, most of amps come with some kind of protection against short-circuits, so in principle the problem should be only one fuse inside. If not, I guess (but I don't know!) that it may be more expensive to fix it than to buy a new one.
    I hope it helps!
     
  4. Reiner

    Reiner
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    Well, I am not a technician, but I have an idea: take a voltimeter (if you want a house-made tester, use a battery and a little lamp) and a cable you know is working. Then, with a very little pin (check first with the tester if it conducts electricity) you may use that circuit including more and more of the damaged cable on each step. Stick one of the ends of the tester to one end of the damaged cable, and the other end of the tester, with the pin, you go pinning each 1 meter, for example. That will tell you in which section it is damaged, but I don't know if that will actually cause more damage.

    I am afraid it won't work: shortcut is shortcut, it don't matter if it's after 1m oder 10m, the tester will always indicate that.
    Thus using a battery and a lamp won't work either as the battery itself will be constantly shortcut.

    Furthermore I think it's unlikely that the cable is at fault - cables don't just go faulty unless it has somehow been damaged.
    Yet I would go along with Jase and check the connections and terminations, not the first time that someone overlooked a tiny strand which caused the whole problem.

    If you want to test the exact point (in case the cable would acutally be at fault) you would need some highly sophisticated test equipment using a DTF (distance-to-fault) measurement - more expensive than a new cable though.
     
  5. sinister_stu

    sinister_stu
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    Reiner is right. It is extremely unlikely that the problem is within the cable. It is almost certain that the problem is at one end of the cable. The only fault that would be likely to occur within the cable would be an open circuit, caused by a break in the cable (even this is quite unlikely).

    I would check both ends of the cable and if you can't see anything untoward then the problem is probably in the speaker's crossover, which I can't help you with.
     
  6. cribeiro

    cribeiro
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    Ups! You are both right! I was thinking about an open circuit, not about a short-cut. I must apologize... But then, that would be easier, at least to know if there is a short cut, but not to locate it: use one end of the cable, and take the pair of wires to close a circuit (of the tester, for example). If that closes the circuit for the other end with both wires open (not touching each other), then you really have a short-cut.
     
  7. coxy

    coxy
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    Thanks guys but have just retrieved cable from under the carpet and have found seven holes in the cable from carpet gripper. Wife has been laying on the carpet in front of the fire!!

    thanks to all!
     

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