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Pioneer VSX-523-K Amplifier - Identify resistors

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    #21
    Re: Pioneer VSX-523-K Amplifier - Identify resistors

    Good idea. I found AGND on both boards. No decernable difference in reading.. all measurements keep simply charging (resistance going up in the meg ohm range)

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      #22
      Re: Pioneer VSX-523-K Amplifier - Identify resistors

      ok... so you check both the main board and the amp board? Next, what do you have available to you in terms of test input signals (ie. 1Khz tone or equivalent) and what do you have in terms of measuring... scope?

      So in your current "state", does your system stay "operational" (ie. no flashing hdmi light) with the previous cable unplugged? without any "sparks / smoke" or have those components been destroyed at this point?.... I am not sure I followed the "loss of some components" a few posts back... was that originally, after you did the "unplug cable" or when?

      Theoretically, IF the system is operational in some form, you should be able to input a signal and pick it up at the main board where the FR,FL, etc come out to go to the amp board. Further, even without an input signal, potentially, IF the main board is functioning in some form, you should be able to check those points for voltages or lack there of... again comparing across the 5 channels to see if anything stands out.

      edit: I misread the schematic... :-( cp402 is the output lines of the amp going back to the main board while cp401 is the input lines to the amp coming from the main board / switching. Sorry.... but I don't see how that cp402 causes something different on the DC_detect lines which aren't in that connector.

      edit: ok I can see where the dc-det lines are on page 50 and since the output lines have been disconnect (cp402), then the two detect lines will see nothing.
      Last edited by budwich; 10-04-2021, 04:05 PM.

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        #23
        Re: Pioneer VSX-523-K Amplifier - Identify resistors

        Originally posted by jason123 View Post
        Good idea. I found AGND on both boards. No decernable difference in reading.. all measurements keep simply charging (resistance going up in the meg ohm range)
        at the amp board, do the same checks (unpowered / unplugged from AC) to the highB "rails" (+/-)... perhaps this will pick up something (a shorted / weak cap)

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          #24
          Re: Pioneer VSX-523-K Amplifier - Identify resistors

          do you have a transistor / cap checker?

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            #25
            Re: Pioneer VSX-523-K Amplifier - Identify resistors

            Originally posted by budwich View Post
            ok... so you check both the main board and the amp board? Next, what do you have available to you in terms of test input signals (ie. 1Khz tone or equivalent) and what do you have in terms of measuring... scope?
            I do have a function generator and a scope, yes.

            Originally posted by budwich View Post
            So in your current "state", does your system stay "operational" (ie. no flashing hdmi light) with the previous cable unplugged? without any "sparks / smoke" or have those components been destroyed at this point?.... I am not sure I followed the "loss of some components" a few posts back... was that originally, after you did the "unplug cable" or when?
            Ok, so I had few popped caps on C channel and FR. I replaced all the E Caps as previous posts. Then I found the biasing transistors on C channel had popped - Replaced those as well along with the 0.47 Ohm resistors (all 4 of them.) Replaced the biasing zeners and diodes at the base of the large transistors and the large transistors. When I got 0 V for bias check as @R_J suggested, I found R25C bad - one on order. During the Bias voltage check, I found that SR channel is the one reading 317mV or so mV on bias pins (should be 2mV). I measured all resistors, and diodes checked out.. so I thought I'd change what controls the bias. I replaced the BJTs A992 and KTA1024 and KTC3206. When I plugged back in, I saw smoke and park in the KTA1024 and KTC3206 region. I replaced these 2 transistors again, but haven't plugged back in AC. Hope this helps in the chronological understanding.

            Theoretically, IF the system is operational in some form, you should be able to input a signal and pick it up at the main board where the FR,FL, etc come out to go to the amp board. Further, even without an input signal, potentially, IF the main board is functioning in some form, you should be able to check those points for voltages or lack there of... again comparing across the 5 channels to see if anything stands out.

            edit: I misread the schematic... :-( cp402 is the output lines of the amp going back to the main board while cp401 is the input lines to the amp coming from the main board / switching. Sorry.... but I don't see how that cp402 causes something different on the DC_detect lines which aren't in that connector.

            edit: ok I can see where the dc-det lines are on page 50 and since the output lines have been disconnect (cp402), then the two detect lines will see nothing.[/QUOTE]

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              #26
              Re: Pioneer VSX-523-K Amplifier - Identify resistors

              quote: "so I thought I'd change what controls the bias. I replaced the BJTs A992 and KTA1024 and KTC3206"

              did you check those to see if they are actually bad... that was related to my question: do you have a transistor / cap checker?

              quote: "During the Bias voltage check, I found that SR channel is the one reading 317mV or so mV on bias pins (should be 2mV)".... but during this effort, you didn't see any "magical smoke / spark"... until you changed out the two transistor in that section... so were the previously ones blown?

              I am sure others might have ideas, but my only one left would be do selective resistance measurements at various points using the highb(+-) as a reference and compare those across channels at various point to see if anything looks out of place.

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                #27
                Re: Pioneer VSX-523-K Amplifier - Identify resistors

                Originally posted by budwich View Post
                quote: "so I thought I'd change what controls the bias. I replaced the BJTs A992 and KTA1024 and KTC3206"

                did you check those to see if they are actually bad... that was related to my question: do you have a transistor / cap checker?
                I have a Cap checker, but no, I do not have a transistor checker. I don't really know that they are bad, I just assumed if I'm getting higher DC, then the bias setting was off??? wrong assumption likely.
                Originally posted by budwich View Post
                quote: "During the Bias voltage check, I found that SR channel is the one reading 317mV or so mV on bias pins (should be 2mV)".... but during this effort, you didn't see any "magical smoke / spark"... until you changed out the two transistor in that section... so were the previously ones blown?
                Correct. No, I do not know that they were bad. I simply had extras so I replaced them.



                Originally posted by budwich View Post
                I am sure others might have ideas, but my only one left would be do selective resistance measurements at various points using the highb(+-) as a reference and compare those across channels at various point to see if anything looks out of place.
                Just to clarify, you're suggesting I make resistor mesurements at various points of the circuit with the negative lead of the DMM referenced to "Highb +" and "Highb -" pins??

                I'm considering rebuilding that channel (main transistors, biasing zeners and diodes) Barring any other component failure (I haven't been able to find any), this should fix it, right??

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                  #28
                  Re: Pioneer VSX-523-K Amplifier - Identify resistors

                  quote: "Just to clarify, you're suggesting I make resistor mesurements at various points of the circuit with the negative lead of the DMM referenced to "Highb +" and "Highb -" pins??"
                  resistance measurements..... You are looking for paths thru components that trace back to power which might mean that potentially that component maybe "less than good" (ie. letting current thru or otherwise, maybe open).

                  As for "rebuilding the channel", I usually try not to disturb existing circuits unless one knows a given component is bad as sometimes one tends to do more damage than repair depending on skills and design / implementation of the circuit..... hence my question around the replacement of components and then subsequent you saw "smoke and sparks" where as before the work, this did not happen. Not meaning that you caused it and things happen but more "why the difference?".

                  My suggestion would be to follow the signal path as outlined in the schematics doing resistance measurements (both from the ground and power "rails" perspective / reference) along the path back towards the "front" on the circuit (ie. where the signal comes in). Comparing those against a working channel (you hope) and see if anything seems "out". The other thing is, if you look at the schematic, most paths have some form of "dc blocks" (ie. caps) in place. IF those are doing their job, then that would tend to point at some places where rails are "leaking" thru some components possibly... again, just a thought.

                  Further to all this maybe, IF you are blowing one channel, what is happening thereafter?... meaning, is the unit shutting down, getting the flashing LED, etc. IF it is remaining operational then you can't do any more damage to the blown channel than has already happened. Take the opportunity, to do some voltage measurements at various "strategic points" to see what's happening. Again... only do this IF you know you aren't damaging the thing further (ie. its stable and not popping channels, one by one).

                  Lastly, as others suggested to me during some of my repair efforts, you could try using a "bulb limiter" to control the amount of voltage (and current to a degree) to allow for powering up in some fashion and perhaps saving some components from failing... depending on what the problem is... of course, it might not help at more "internally" oriented components versus output ones.

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