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Denon 455 hiya robotek i have the same problem as everyone else it seems unit comes on with red led makes a click as transformer gets power but nothing else.I read on the forum that you can help if i have a multi meter which i have.So if you could help me i would be eternaly gratefull as the wife is giving me an earfull to either get it fixed or dump it. Thanks John johncmorgans@ntlworld.com

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  • john morgans Jan 25, 2009

    i used to repair televisions for a living so i am fairly good at electronics so any help you could give would be nice



    John

  • john morgans Feb 12, 2009

    thanks for your help but...............

    i get 240volts in but nada out the 12volt relay is switching which is the noise i could hear i seem to have power across the mains switch but nothing going to the board even when i unplug it nothing there i thought it could be a load fault but was wrong.



    as for the suggestions you made i would be happy yo do them if i had any power to the pcb



    Cheers



    John

  • john morgans Feb 12, 2009

    just a bit more i am getting 5volts supplied by the front pcb but nothing else so does that prove that the transformers are ok?



    because i am starting to think that 1 of them is open circuit there is a small 1 which supplies 240 volts to the big 1 also supplies on off switch has the 12 relay on same pcb



    john

  • john morgans Feb 22, 2009

    dumped it sorry

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Hi John
For sure, can at least get an understanding of what may be wrong. You hear the power relay click in, but perhaps no secondary click of the speaker protection relay.  This is generally caused by a fault condition in the amp, resulting in a DC offset voltage being present in the speaker outputs, then detected by the protection circuit, does not allow the speakers to be connected to protect them from damage.  . How far do you want to get into it?
regards robotek

Posted on Jan 25, 2009

  • Graeme Ross
    Graeme Ross Jan 25, 2009

    No worries, And I hope that I can earn that Fixya for my efforts to help you:) Maybe you can pass on to the missus my optimism my optimism that it that it can be fixed, and that YOU are going to do it :) 


    .  I take it that the speaker protection relay is not engaging... no momentary pause, then click when you turn the amp on. Can you confirm that with me. If NOT then we would like to check to see which output stage has a DC offset. Pop JUST the lid off, and look for a air cored copper zobel network coil, or a double low value ceramic  5 watt power resistor (may be 2 single resistors connected together) of less than 0.5 ohm. is effectively the speaker output prior to the protection relay for each channel here.  Measure for voltage here before disturbing anything. This is to quickly determine which channel is faulty per the PCB,and confirm that there is a DC offset problem. If you measure anymore than a few millivolts at this point, that is the offending channel. 


    Check for burnt resistors about the output stages to also confirm which channel is faulty. Once done, and you are confident that you know which channel is the faulty one, you need to get to the PCB side of the amp by removing the bottom cover and check with strong light and fresh eyes for dry solder joints about the offending output stage. I should also remind that you to work electrically safe. 
    Get back to me here with your findings if you like. I will be in and out a bit today (6.00am here now) and we can go from there. Oh and I was serious about working for a FixYa. Any chance of an upgrade:)

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