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  • Amp problem

    Hi guys, I have an old nad 2400 amp, and upon startup (most notably after it had been running, turned off for 30 secs to switch speakers, and back on) the transformer briefly hums and vibrates. What is the cause of this? I'm suspecting it's worn out ps caps but not sure..

    Also the last time I turned it on it let out a little magic smoke from I don't know where. I turned it right back off and not back on since. It was sounding great, powerful and dynamic, up to this point. Nothing looks toasted inside, but there are a couple tiny resistors inside that have discolored the board from heat.

    Any thoughts? - besides throw it away and buy something that isn't 30 years old!
    Projects:

    transcenD: http://techtalk.parts-express.com/fo...5035-transcend
    Summits: http://techtalk.parts-express.com/sh...75-The-Summits
    References: http://techtalk.parts-express.com/sh...-My-References
    Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

  • #2
    Originally posted by dynamo View Post
    ... besides throw it away and buy something that isn't 30 years old!
    I just fixed one of my amps that is over 32 years old
    Find a schematic.
    Take a meter an measure for Value and "open" ( may be the symptoms and not the cause however ).
    It does sound like the P.S. took a Shite.
    "Not a Speaker Designer - Not even on the Internet"
    "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

    Comment


    • #3
      Sounds good, thanks. I'm not sure how much time I want to put into it and I may just sell it for parts or repair. I just kind of want to get some ideas and direction from you guys in case I did want to get it fixed.

      I was actually using it a little for the first in a long time because it's been in the spares pile and I was planning to sell it so I was making sure it was solid before I sold it to somebody. Glad I did test it myself for a while so I had this issue now and not the person who bought it.

      I wasn't indicating things 30 years old aren't worth repair (many times I would choose the 30 year old piece over a new one), just kind of being tongue in cheek about my situation. It really is a bummer though because for an 80s mid-fi piece, it really sounded great.
      Projects:

      transcenD: http://techtalk.parts-express.com/fo...5035-transcend
      Summits: http://techtalk.parts-express.com/sh...75-The-Summits
      References: http://techtalk.parts-express.com/sh...-My-References
      Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

      Comment


      • #4
        Honestly modern electronics don't often lend themselves to repair.
        The fix on my Hafler was 1 resistor
        "Not a Speaker Designer - Not even on the Internet"
        "If the freedom of speech is taken away, then dumb and silent we may be led, like sheep to the slaughter."

        Comment


        • #5
          Those resistors might be part of the problem I would check to see if they opened up. You might also want to go through the power section and measure capacitors to make sure they are still in spec. I would also take a close look at any I.C. that is in the power section to make sure that it isn't bubbled or charred indicating a failure.
          Did you hook the amp up to a lower ohm speaker then they are rated for or push the amp into a clipping mode? That might help us identify what went wrong with the amplifier.

          Comment


          • #6
            NAD 2400 Service Manual (w/schematic) pdf.

            https://drive.google.com/open?id=0B0...Fk2RVNlMnlrNjg

            Comment


            • #7
              Thanks for all the insight guys! And that schematic!

              I was just looking for ideas of possible problems but you are giving me the itch to prod into the problem instead of selling it for parts. Full disclosure though is that it will be a while before I get to it, ahead of it in line is my basement I am finishing, hanging Sheetrock in my 24x28 shop, my five speaker projects I have all started, my unfinished yard, and my broken tractor needed for the yard. Boy I suddenly feel overwhelmed!
              Projects:

              transcenD: http://techtalk.parts-express.com/fo...5035-transcend
              Summits: http://techtalk.parts-express.com/sh...75-The-Summits
              References: http://techtalk.parts-express.com/sh...-My-References
              Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

              Comment


              • #8
                Originally posted by kenrhodes View Post
                Those resistors might be part of the problem I would check to see if they opened up. You might also want to go through the power section and measure capacitors to make sure they are still in spec. I would also take a close look at any I.C. that is in the power section to make sure that it isn't bubbled or charred indicating a failure.
                Did you hook the amp up to a lower ohm speaker then they are rated for or push the amp into a clipping mode? That might help us identify what went wrong with the amplifier.
                The speaker hooked up was a safe stable load. Those amps have protection and are very stable, so I definitely suspect an age related failure. Those hot resistor areas are both similar looking tiny resistors, look like1/8 watt. When I get time I'll look at them since I think the board says which ones they are and look at the schematic posted by millstonemike.
                Projects:

                transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                References: http://techtalk.parts-express.com/sh...-My-References
                Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                Comment


                • #9
                  something that old, in the psu section i would replace input and output caps. as there is cap aging and causes them to lose storage if you will. i would replace resistors as well since with age they can resistance up or down from where they are at. that might also be why some of them burned the board as resistance might have dropped low enough at some point to cause a high current to pass through to heat them up like that.

                  Comment


                  • #10
                    That amp is useless. Send it to me and I'll properly dispose of it for you. It will look great next to the twin NAD2100's I refurbished.

                    I'll even send you my FedEx account so you don't have to pay for shipping!



                    In all seriousness - replace virtually evey cap on the board, especially those in the power supply section.

                    Discolored resistors are normal due to the power dissipation that some are required to take, but they should be looked at to check their value.
                    DARPA Jr - 2015 InDIYana Winner - RS180-8 + RS100P-8 + ND25FA
                    The Aria's - RS150-4 (or RS150-8) + XT25SC90
                    The Mariposa's - TEBM65C20F-8 + ND16FA
                    The Canzonetta's - RS100P-8 and ND16FA
                    AudioSource AMP-100 Mods OR Pyle PAMP1000 Mods

                    Comment


                    • #11
                      Originally posted by Mike E View Post
                      something that old, in the psu section i would replace input and output caps. as there is cap aging and causes them to lose storage if you will. i would replace resistors as well since with age they can resistance up or down from where they are at. that might also be why some of them burned the board as resistance might have dropped low enough at some point to cause a high current to pass through to heat them up like that.
                      Good ideas, thanks!
                      Projects:

                      transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                      Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                      References: http://techtalk.parts-express.com/sh...-My-References
                      Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                      Comment


                      • #12
                        Originally posted by tyger23 View Post
                        That amp is useless. Send it to me and I'll properly dispose of it for you. It will look great next to the twin NAD2100's I refurbished.

                        I'll even send you my FedEx account so you don't have to pay for shipping!



                        In all seriousness - replace virtually evey cap on the board, especially those in the power supply section.

                        Discolored resistors are normal due to the power dissipation that some are required to take, but they should be looked at to check their value.
                        Lol, I was waiting for an offer to unburden me of it. I'll keep it in the to do pile for now, but thanks for the offer
                        Projects:

                        transcenD: http://techtalk.parts-express.com/fo...5035-transcend
                        Summits: http://techtalk.parts-express.com/sh...75-The-Summits
                        References: http://techtalk.parts-express.com/sh...-My-References
                        Vintage Style 2-way: http://techtalk.parts-express.com/sh...-vintage-2-way

                        Comment

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