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    Sony amp "protect" issue

    First of, I have no idea what happened.
    I used the amp yesterday afternoon and it was perfectly fine.
    Then I switch it on this morning and it won't work.
    It's a Sony STR-DE515 that I bought three years ago.
    Whenever you turn it on, you have to wait a few moments, then you hear a relay click and you get sound however as of this morning when you turn it on and wait a few moments you don't hear a click, instead it blinks "PROTECT".
    I opened the case and saw nothing visually bad (at a glance) and I hit it a few times, just in case the relay was somehow stuck. That didn't work either.
    Visually all the caps look okay and I don't smell anything burnt so nothing went poof.
    What happened? Did the output transistors or something go?
    My entire home theater system is effectively useless without this receiver and I don't have the budget to buy another one.
    Find Nedry!


    Check the Vending machines!!

    <----Computer says I need more beer.

    #2
    Re: Sony amp "protect" issue

    Maybe the transformator got too hot or overloaded: try unplugging the power cable for 2 or 3 hours, then check all cables (e.g. loose conncections, bad rca plugs and such).
    If this don't work, I found something on a forum [1]: it seems some caps and resistors may be damaged.

    Zandrax

    [1] http://forums.afterdawn.com/thread_view.cfm/99866
    Have an happy life.

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      #3
      Re: Sony amp "protect" issue

      Well leaving it unplugged didn't help (as I expected as it was well ventilated, as an amp should be) and I didn't see any similar damage like that other guy had.
      Find Nedry!


      Check the Vending machines!!

      <----Computer says I need more beer.

      Comment


        #4
        Re: Sony amp "protect" issue

        The service manual is offered here:
        http://cgi.ebay.com/Sony-Receiver-ST...2em118Q2el1247
        It's easy enough to lift the legs of the outputs.
        Just takes a few minutes, then plug in the headphones and plug in the unit.
        It tells you where the problem is and allows you to test each output pair.
        Jim

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          #5
          Re: Sony amp "protect" issue

          Sorry but I'm not purchasing the service manual.
          Find Nedry!


          Check the Vending machines!!

          <----Computer says I need more beer.

          Comment


            #6
            Re: Sony amp "protect" issue

            Did you read this?
            https://www.badcaps.net/forum/showthread.php?t=4230

            I found lots of bad solder joints.

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              #7
              Re: Sony amp "protect" issue

              Okay then, I guess I'll take the rest of the unit apart and inspect it a little more and keep out for bad joints.
              Find Nedry!


              Check the Vending machines!!

              <----Computer says I need more beer.

              Comment


                #8
                Re: Sony amp "protect" issue

                First off I found the service manual for the receiver here.

                Okay so I went and pulled the main PCB from the unit and dusted it off.
                For starters, pretty much all of the caps in this are either Nichicon or Rubycon.
                I can also now see that the area around IC701 is a bit brown and so is the area around R807-R809 and C801.
                Other than that I see no charred parts nor do I see any cold joints (but I bet you there are at least two hiding on this board).

                EDIT: Looking at the diagram for IC701 there is something inside the IC marked "protector". I think this might be it.
                Find Nedry!


                Check the Vending machines!!

                <----Computer says I need more beer.

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                  #9
                  Re: Sony amp "protect" issue

                  Reason it went into protect mode is the outputs either failed or leaky or open and drive circuit went out of tolerances or blown in act of the main outputs failure. When this happens, you will see DC of some voltage instead of very small millivolts on the output terminals.

                  Cheers, Wizard

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                    #10
                    Re: Sony amp "protect" issue

                    When you mean output terminals you mean the speaker jacks?
                    Will plugging a voltmeter into the speaker jacks determine the problem?
                    Just want to know as I have the whole unit disassembled and I don't to be putting it back together, only to tear it apart again, over and over.
                    Find Nedry!


                    Check the Vending machines!!

                    <----Computer says I need more beer.

                    Comment


                      #11
                      Re: Sony amp "protect" issue

                      Okay, I partially reassembled the thing (screwed the board back into the case) and then plugged my voltmeter in to the left speaker jacks. With the system off it's reading .29 volts.
                      After switching it on it jumps to 1.4 volts.

                      EDIT: I did it again and this time I didn't get the protect until AFTER I hear that relay click, at which point it jumps to 1.66 volts and then a moment later I hear the relay click again and "PROTECT" blinks on the screen. I also have two heatsink clips on IC70 to dissipate any heat it's generating.

                      EDIT, AGAIN: I don't know what I did but it's working now.
                      For the heck of it I'll let it warm up and play with the volume a bit and then reheat the joints on IC701 as I did wiggle it a few times. I might also look into gluing a heatsink onto IC701.
                      Find Nedry!


                      Check the Vending machines!!

                      <----Computer says I need more beer.

                      Comment


                        #12
                        Re: Sony amp "protect" issue

                        Okay, now I got it to a point where it's intermittant.
                        Sometimes it will go into circuit protection immediately, other times it takes a few more moments.
                        Find Nedry!


                        Check the Vending machines!!

                        <----Computer says I need more beer.

                        Comment


                          #13
                          Re: Sony amp "protect" issue

                          Originally posted by pentium
                          Okay, now I got it to a point where it's intermittant.
                          Sometimes it will go into circuit protection immediately, other times it takes a few more moments.
                          Hmm ... fake contacts kept in contact by the heatsink? Overheat? Really I have no clue

                          Zandrax
                          Have an happy life.

                          Comment


                            #14
                            Re: Sony amp "protect" issue

                            1.6 is too high of offset. should be very small volts floating in millivolts like .03V or so.

                            Tear it completely apart but keep heatsinks on the power modules if it is hard to take apart so you can see all the solder points and go over them with your magifying glass and resolder bad joints. Sony is famous for this.

                            Majority of audio ampifers are totem pole transistors ampifer between 2 isolated supplies (+ and -) and drive one side of the speaker from midpoint of the totem pole ampifier to the ground.

                            For this reason, the checks is to see why amp is going into protect is this.

                            When it's working right, the two ampifier transistors are being driven EQUALLY at rest making some heat and floating very small volts at the point in respect to ground potiential. Also it ahs extra circuits to make the cross over point LEAST distortion (no hump or lumps in the waveforms at the zero crossings).
                            This is where lot of work is spent for BEST quality audio and this is where cost makes the difference betwene lousy one and the NICEST sounding ones.
                            Also the drive circuits quality do matter not to "color" the audio.

                            Cheers, Wizard
                            Last edited by Wizard; 09-04-2008, 07:37 PM.

                            Comment


                              #15
                              Re: Sony amp "protect" issue

                              I'm a little lost here.
                              I already managed to completely pull the main PCB out and I have gone over the board at least twice.
                              Could you at least narrow down the places to check by pulling an image out of the service manual and circling it for me?
                              Find Nedry!


                              Check the Vending machines!!

                              <----Computer says I need more beer.

                              Comment


                                #16
                                Re: Sony amp "protect" issue

                                You haven't detailed the design of this amp.

                                Is it BIG black ICs with row of pins for each? or many individual transistors (big ones on the heatsinks)?

                                At any rate we mean the drive circuits that forms correct signals to take out the zero crossing distortation that drive the main POWER ampifiers. Bad joints is very fine crack on hot stuff and any that vibrated loose. Need magnifying glass (5X or 10X).

                                detail on the push/pull (aka totem pole output)...this is vast majority of A and AB class amps out there. There are chopper output ampifiers using a coil and fake out a audio waveforms to the speakers that's another different ball of wax thing to discuss later.

                                http://en.wikipedia.org/wiki/Class_A_amplifier#Class_A

                                Cheers, Wizard
                                Last edited by Wizard; 09-05-2008, 10:29 AM.

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                                  #17
                                  Re: Sony amp "protect" issue

                                  Okay, the part that I seem to be the most concerned about is the vertical standing IC seen in the center of this photo.



                                  It is the one that gets hot (you can see the PCB under it is a little brown)
                                  Find Nedry!


                                  Check the Vending machines!!

                                  <----Computer says I need more beer.

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                                    #18
                                    Re: Sony amp "protect" issue

                                    All of the area, yours is descrate transistors for amp on (heatsink).
                                    I'm talking about WHOLE lot of stuff between the signal to the drive circuit and the ampifiers. Bunch of resistors, transistors, inline IC, and small transistors (TO-92) etc.

                                    Not small area. Whole. Because one of them have bad joint somewhere. And others are close to break solder joints too. That why need to inspect real carefully.

                                    And yes, Sony is SLOPPY wth heatsink grease! :p

                                    Cheers, Wizard

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                                      #19
                                      Re: Sony amp "protect" issue

                                      Wait, so you pretty much recommend I go with the iron and just reheat every joint on the board?
                                      I really did not understand your last post.
                                      Find Nedry!


                                      Check the Vending machines!!

                                      <----Computer says I need more beer.

                                      Comment


                                        #20
                                        Re: Sony amp "protect" issue

                                        LOOK! you will find cracks and iffy looking solder joints. Need magnifying glass to find these. I did say the whole area that you taken the picture for this. This means the circuits for the row of big transistors, area about 3" out in front of them.

                                        These are our daily job to search for these bad joints (usually the first thing to do) and check components are in spec with ohm tests and diode checks (transistors are like 2 diodes too).

                                        Cheers, Wizard

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