Pioneer SX-550 Issues

Discussion in 'Pioneer Audio' started by TPN, Sep 16, 2018.

  1. TPN

    TPN New Member

    Messages:
    5
    So whilst this is a little over my pay grade, I'm giving it a whiz at repairing this beautiful receiver.

    I found this at a charity shop and decided to pick it up. At first, it would do the thing that's most common for these SX-550s to do, flicker the power light. I managed to fix that issue, but now have another issue that I must admit, I don't quite understand.

    Once I got this to power up, the left channel was highly distorted, and was quite a bit lower in volume compared to the right channel. I've tested all the different inputs, and it doesn't change no matter the input (including radio.) When testing using the headphone output, it works fine. Both channels sound reasonably great. No distortion, and both are same volume to each other.

    Now, I am unsure if the outputs for speakers at the back and the headphone use the same circuit, looking at the circuit diagram, it looks like they do but again, I am no expert, just my first repair project on something like this, so I am more than likely wrong on this wrong.

    Going with that mindset, I was tracing the back of the board as best I could, and to be quite honest, it doesn't look right to me. It looks like there has been some sort of liquid or something spilt as the back of the board looks quite bad, and some of the traces look as if they have been slightly eaten through with something corrosive. (Included some pictures of the back of the board.)

    I will also add that, it's only I guess the audio side of the board that looks this way. Looking at the opposite end of the board, there is nothing on it, it looks fine.

    If anyone would be able to shed some light on this for me as to what the issue might be, that would be excellent.

    Thank you!
     

    Attached Files:

     

    Please register to disable this ad.

  2. Watthour

    Watthour Electron Rancher - JS3600

    Welcome Aboard!

    The photos appear to show possible heating or corrosion in a couple areas. Fortunately, it appears to be minor.

    The symptoms you are describing would seem to indicate a problem with an output transistor(s). Noticeable distortion with speakers and almost no distortion on headphones is a classic symptom of damaged outputs and/or drivers. If you have a meter handy it should be a fairly easy analysis. Access to the devices can be a little tight, but if you've been through the power switch you're probably already aware of that:

    [​IMG]


    Fortunately, repairs are relatively inexpensive. I've had two 550s in the same condition. The final output stage 2SD526 and 2SB596 devices can be successfully replaced with MJE15032G/MJE15033G - About $1.60 apiece. The driver stage 2SC1211 and 2SA697 can be replaced with KSC2690AY and KSA1220AY, for about 50¢ each. Of course, before ordering parts it will be advisable to completely diagnose the problem(s) and anticipate and upgrades you may want to perform. I have suggestions.
     
  3. TPN

    TPN New Member

    Messages:
    5
    Thank you for the response! Gives me something to start with now. I shall look at this over the week and report my findings!
     
  4. TPN

    TPN New Member

    Messages:
    5
    So, I had a short little look around today, just wanted to make sure that I am looking at the right thing before I continue. I've included pictures about what I think it is.

    From looking around on the internet at the original parts numbers though, I feel that I am wrong.

    Thanks
     

    Attached Files:

  5. inductor

    inductor Super Member

    Messages:
    1,548
    Location:
    uk
    boards look ok apart from dry loints
     
  6. TPN

    TPN New Member

    Messages:
    5
    Alrighty, well I finally have got around to checking the parts, and most of them seem to return bad. So, hopefully the order parts will fix that. I shall post an update when all comes and are installed.
     

     

    Please register to disable this ad.

  7. TPN

    TPN New Member

    Messages:
    5
    I hopefully intend to remember to touch some up when I install some new parts. Seems good otherwise on the opposite board.

    I get the feeling that someone has already been in here so maybe some of the joints look bad because of them, I don't know though.
     
  8. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,787
    Location:
    Las Vegas Nevada
    It looks like it's been repaired at least once before. The outputs are not matched devices and not the same components Pioneer would have used. At least that what appears to me.
    I would reflow all the connections on the main board as well. I wont take that long to do, small receiver.
     

Share This Page