Denon PMA-1560 other channel dead

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  • OniJon
    Computer Expert
    • Jun 2012
    • 82
    • Finland
    #1

    Denon PMA-1560 other channel dead

    One burnt main transistor, with a blown leg, TR525 blown leg, resistor R551 blown.
    I'm a second owner of this amp, somebody "tried" to repair it already. I've removed few carbonfilm resistors because they showed nothing on DMM. Also metallized paper caps went out the window. Total recap is in order of course and I'll change the carbon resistors for something better.

    Question is, when I get to it, what are the pre-transistors that affect the sound the most? I've read that these need to be gain matched if it comes to that, how to do that the easy way?

    Power transistors gotta go also because original SanKen's are hard to get and crappy anyway. Good subtitutes (what I've read and heard): 2SA1492 -> 2SC5242 or 2SC1962 and 2SC3856 -> 2SC2723
    That's a problem for another time, but any tips and tricks how to proceed after changing all the crap from the board and repairing some damage, are welcome.
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    • OniJon
      Computer Expert
      • Jun 2012
      • 82
      • Finland
      #2
      Re: Denon PMA-1560 other channel dead

      I've measured most of the carbon resistor in megaohms, so they're definitely goners. Somehow the bias resistor 3DR18R18, ceramic type, is also changed to inductive type frankenstein. Should I just try to get 2 normal non-inductive ceramic type resistors that are over 2W?
      I've tried to find something from Farnell (element14) but can't find anything suitable. How about something like this? How accurate this resistors value needs to be?
      http://www.ebay.com/itm/153123183757
      http://www.ebay.com/itm/184191408413

      This is spot on, but I don't need 25pcs
      http://www.ebay.com/itm/153434145384

      Also, what possible replacements are there for J79 (TR521) and K216 (TR519)? I've found several but all with wrong leg order. These little weirdos made by Hitachi, have source as center leg, where as all that I've found have gate in the middle. Of course I could just snap the legs short and cross these two with a pieces of wire.
      Last edited by OniJon; 03-22-2020, 06:32 AM.

        Comment

        • CapLeaker
          Leaking Member
          • Dec 2014
          • 7988
          • Canada
          #3
          Re: Denon PMA-1560 other channel dead

          sometimes you cant get around the leg order. if i cant get the right leg order, i try to get one that has a backward leg order. then i just have to solder the transistor in backwards, not having to deal with crossed legs.

            Comment

            • OniJon
              Computer Expert
              • Jun 2012
              • 82
              • Finland
              #4
              Re: Denon PMA-1560 other channel dead

              I've been soldering in new metalfilm resistors to replace carbon ones, wima's for plastic caps and few(most) bad electrolytics have been replaced with Panasonic/Nichicon/NCC. Now I'm wondering about the transistors. I need to replace TR525 which is 2SD2004 but it needs complimentary pair or I need to buy original which is kinda expensive. Any thoughts?
              As for the power transistors I've chosen to replace Sanken 2SA1492 + Sanken 2SC3856 with Toshiba 2SA1986+ 2SC5358. Any thoughts on this?

                Comment

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