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    Pioneer SX-300, stereo receiver

    Wanted to post this as a little project for your eyes and also for anybody who might have similar problems with the amplifier, this or other model of Pioneers SX series.

    The main problem was "hissing" sound or somekind of low noise on the right channel. I thought that it was just leaking caps and went right away to change every electrolytic I found.

    It was pain in the ass to do, because not all of them were possible to change underside. I needed to remove the amplifierboard and to do that I had to cut the wires or remove them from the taps. I took notes and draw what goes where. After the testing, it wasn't the caps. Noise wasn't still gone, I was getting frustrated already because the unit cost me nothing and some of the caps were pretty pricey.

    Then I figured to read some forums on the net that some other guy had the hissing thing too and he was advised to replace all of the noisy NPN transistors, 2sc1344 and 2sc1345. There were 8 pieces of 1344 and two 1345's. I figured that 2sc2240 is better and matching, it also has same leg order. I ordered 15 of 2240's and when they arrived I just checked the B-C-E right, put them right in, cleaned the underside of the board with nailpolish remover (acetone free).

    I was so sure that I've made a mistake and thing would explode after I hit the switch but luckily this wasn't the case. I measured voltages from the outputs, that I wouldn't burn my speakers. Everything looked fine and I connected the speakers, luckily I didn't do mistakes and out comes the music!

    Some pics of the (almost) finished product for your eyes to feast on! I also changed the old wire with round plug that didn't have grounding to a IEC socket with filtering. Can be seen on the pics.
    The thing with black background will be laminated or lacquered on top of the unit because I painted the front black.
    Attached Files
    Last edited by OniJon; 10-19-2012, 03:30 PM.

    #2
    Re: Pioneer SX-300, stereo receiver

    Yep, those old transistor when they go bad, they make something like frying noise, if you have cold spray, you can make it act up more. If you look at the legs, they will kind of blackened and not clean tin looking.
    In the mean time you may also want to clean Tape monitor, muting switches and all the pots if you notice the sound cuts out. I still have my Pioneer, Sansui, Yamaha stuff from the 70's and 80's that were built like a tank not like the new 1000 Watts amp that weight 20 Lbs.
    Never stop learning
    Basic LCD TV and Monitor troubleshooting guides.
    http://www.badcaps.net/forum/showthr...956#post305956

    Voltage Regulator (LDO) testing:
    http://www.badcaps.net/forum/showthr...999#post300999

    Inverter testing using old CFL:
    http://www.badcaps.net/forum/showthr...er+testing+cfl

    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
    http://s807.photobucket.com/user/budm/library/

    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment


      #3
      Re: Pioneer SX-300, stereo receiver

      Originally posted by budm View Post
      Yep, those old transistor when they go bad, they make something like frying noise, if you have cold spray, you can make it act up more. If you look at the legs, they will kind of blackened and not clean tin looking.
      In the mean time you may also want to clean Tape monitor, muting switches and all the pots if you notice the sound cuts out. I still have my Pioneer, Sansui, Yamaha stuff from the 70's and 80's that were built like a tank not like the new 1000 Watts amp that weight 20 Lbs.
      I cleaned the pots, they had a ton of carbondust. Just sprayed CRC the hell out of them and wiggled back and forth. Now they work like a charm again.

      And the transistor legs were black, like you said. This was my first amp repair of this kind so didn't know what to look, lol.

      Comment


        #4
        Re: Pioneer SX-300, stereo receiver

        Good job on a nice bit of equipment there!

        BTW, I think the transistor legs turn a blackish color just from oxidization - I don't think it means that it is bad. I have seen this on LEDs and diodes too - all of them still good.
        Muh-soggy-knee

        Comment


          #5
          Re: Pioneer SX-300, stereo receiver

          The cases are supposed to be hermetically sealed. If that fails (indicated by the blackening on the leads), it could cause a lot of problems.
          Last edited by tom66; 10-20-2012, 08:40 AM.
          Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
          For service manual, schematic, boardview (board view), datasheet, cad - use our search.

          Comment


            #6
            Re: Pioneer SX-300, stereo receiver

            The one with the blackened legs are always the one with white noise or cracking noise, I believe they were just poorly seal from the Japanese transistors in the 70's, I replace so many of them due to noise problems.
            Last edited by budm; 10-20-2012, 11:03 PM.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #7
              Re: Pioneer SX-300, stereo receiver

              Some "Links" for ya, Oni:

              http://www.hifiengine.com/forum/mara...-channel.shtml

              http://tapeheads.net/showthread.php?t=7197

              http://www.audiokarma.org/forums/arc.../t-272303.html

              KSC1845s work fine. Even a plain '945 can work, depending on the circuit and how "tight" the bias spread can be.

              Nice job.

              I always thought the leads on those old transistors start corroding, and follow the lead up into the case. Bad news for what's inside...
              "pokemon go... to hell!"

              EOL it...
              Originally posted by shango066
              All style and no substance.
              Originally posted by smashstuff30
              guilty,guilty,guilty,guilty!
              guilty of being cheap-made!

              Comment


                #8
                Re: Pioneer SX-300, stereo receiver

                2SC945 and 2SA733 were real popular in Japanese Stereo systems.
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment


                  #9
                  Re: Pioneer SX-300, stereo receiver

                  Originally posted by kaboom View Post
                  Some "Links" for ya, Oni:

                  http://www.hifiengine.com/forum/mara...-channel.shtml

                  http://tapeheads.net/showthread.php?t=7197

                  http://www.audiokarma.org/forums/arc.../t-272303.html

                  KSC1845s work fine. Even a plain '945 can work, depending on the circuit and how "tight" the bias spread can be.

                  Nice job.

                  I always thought the leads on those old transistors start corroding, and follow the lead up into the case. Bad news for what's inside...
                  Yup, they were totally black. When removing the transistors, the black stuff came off by twisting the legs. The cases of the transistors didn't look too good either.

                  Anyhow, the amp sounds very powerful for a 8 watt machine per channel. It also has very nice warmth and tonality on the midrange. Not that dryness of the D-class amps.

                  Comment

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