reciever repair question

Discussion in 'AV Receivers' started by Ben_Beckey, Nov 26, 2005.

  1. Ben_Beckey

    Ben_Beckey Auditioning

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    Hopefully this is the right forum to post this in...

    My girlfriend has a Sony STR-K502 reciever she bought around 5 years ago (she estimates) that was part of a HTB. Since I've known her (~8 months) the two front speakers haven't worked. It's always bugged me a little (I'm anal like that), but now that winter's coming we're going to spend a lot more time indoors and I want those speakers to work! [​IMG]

    I've already tried connecting different speakers and wires - it's definitely an issue with the reciever. What I'm wondering is what I can do to troubleshoot the thing - is there any easy repairs I can check? Fuses, etc? I'm a big computer geek and have no problem fixing PC-related problems, but am somewhat of a virgin when it comes to messing with home theater equipment. Obviously, I can hook it up and all that, but the repair side is foreign to me. I'd like to learn, though, so...

    If anyone has any tips or simple things I could check... or could let me know where to start looking at why those 2 speakers aren't working, that'd be awesome.

    If I need to post this somewhere else, please let me know or (mods) move it. Thanks!
     
  2. Steve Berger

    Steve Berger Supporting Actor

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    Some common problems are solder connections on the relays and on the jacks themselves (input and output). You could try tapping on the relays. If I remember correctly, these models don't have a removable bottom panel, making resoldering a difficult job (requiring removal of the circuit board from the chassis).
     
  3. Cees Alons

    Cees Alons Moderator
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    Assuming you have tested the speakers and you're certain they are "in working order". [​IMG]

    Do the speakers have the proper impedance for this receiver (I assume, the answer is yes).

    Is the "setting" of the receiver right? Most receivers have a setting function which allows you to state that you have none or one subwoofer, that you have surrounds or not, that you have a center speaker or not, or even that you only have one (mono) center speaker (additionally, it's also possible to define the speakers as "small" or "large").

    If all that is correct, than check if there's a button (switch) to manually switch some of the speakers on or off (sorry if this sounds trivial). There may be a switch labeled "Mono" (which should be off).

    Oh, and yes, a fuse (makes slightly less sense, because both mains aren't working).

    Only after all this would I even think of trying to open the case. Again: I cannot understand very easily why both would be broken, but it is possible, e.g. if a twin end-stage is broken.


    Cees
     
  4. Ben_Beckey

    Ben_Beckey Auditioning

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    Thanks for the replies - will check all those things and then report back. Just wanted a little better idea of where to really start looking at all this. A little more info:

    All 5 speakers are the same (small HTB speakers) - I get a *tiny* bit of sound out of the surround speakers, normal volume out of center, but nothin' out of the mains.
     
  5. Steve Berger

    Steve Berger Supporting Actor

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    Some items specific to this model. Plugging headphones in will turn all speaker relays off. (tried headphones? same output IC, different relay) All fuses are in the power supply and any fuse failure will kill all speaker output. The surrounds and/or center are working? In "normal surround" all dialog will be sent to the center not L/R front.
     
  6. Ben_Beckey

    Ben_Beckey Auditioning

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    Okay, that last post was kinda dumb... I get normal volume out of the surround speakers (the source when I was checking earlier just didn't send much out of them).

    I went through the reciever's setup - had it run the 'test' noise (static) to each speaker. The mains get nothing at all, everything else is fine.

    I didn't see a mono switch anywhere, and I checked everything else, so I went ahead and opened it up. I'm good about not getting in over my head, so I've taken a look around but haven't touched anything. I'd definitely have to take the board out of the chassis to do any soldering or anything like that.

    I don't know a lot about the components of an amp/reciever, so I'm not going to pretend to. [​IMG] If the problem is a twin end-stage, what am I looking for? Any physical clues I would be able to identify? I don't even see any fuses in this thing (I have a feeling that comment is going to make me sound foolish, but oh well).

    Anyway, I don't really think this thing is worth having a pro repair since we could pick up a much better reciever (like the Panasonic sa-xr55) for like $200 or so. I'd like to learn more about the innards of these things anyway, so... advice on where to go from here is appreciated. If I should just give up, I can accept that for now (I guess), though I'd really like to have the experience of actually fixing this thing.

    Thanks again for the replies thus far.
     
  7. Cees Alons

    Cees Alons Moderator
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    Ben,

    Did you also find the setup part, or selection button, or whatever, where you can say "subwoofer - none" and perhaps choose the mains: "large" or "small", or, hopefully, "none" too?

    Or at least, are you sure it isn't there? Most receivers have something like that.

    (The end-stage is the part of the circuit where the leads to the associated outputs are almost directly coming from.)


    Cees
     
  8. Steve Berger

    Steve Berger Supporting Actor

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    First thing to try is a set of headphones. If they don't work then you have an electronic failure in the driver or output circuit. If they work then RY701 is probably the culprit (soldering, broken, failure of relay drive transistor).

    I have the schematics and service manual on this unit since I was an authorized Sony servicer for 25 years.

    There is a single decoder IC for all outputs. If this is bad then you're not going to be able to fix it. There are three driver IC's; one for center (stk350-230) one for all left speakers (main and surround type-upc2581 labeled ic701) and one for all right speakers (main and surround type-upc2581 labeled ic702). Since you have lost both mains but neither surround these are probably OK.
    Since any outputs work then the power supply is OK (all outputs use the same power supply).
    It's not a bad headphone jack or speaker select switch because that would turn all the speakers off.
    The only things common to just the front mains are the decoder and the relay RY701. (little plastic box next to large capacitors on main board)
     
  9. Ben_Beckey

    Ben_Beckey Auditioning

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    Yep, went through the setup... everything as it should be.

    Steve - wow, lots of great info. Not going to lie - some of it's a little over my head. My girlfriend lives 3 hours from me, so I just see her on the weekends - I'll have to bring up some different tools (soldering iron, etc) next weekend to take a look at the things you mentioned.

    Just a quick question, since you obviously really know your stuff - any good books are other places I could start to get to the point where I can service this type of thing myself? I've always been big on trying to learn to do things myself, but always want to make sure I'm doing them the right way.

    I'll post back to this thread by next weekend at the very latest - thanks again guys!
     

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