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Peavey XR8600 one channel down

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  • Peavey XR8600 one channel down

    Hello all
    I know i post about this one a few weeks ago, But i'm really stuck on this and the original Post i made has sadly little help,
    I'm completely lost on this one

    This amp came in with a blown fuse, Replaced fuse and with lamp limiter on can see excessive current draw
    On removing covers i found that one channel was down, with that disconnected i can test the amp so i know one channel is good and one blown

    I found one of the bridge rec s/c , Replaced that still drawing excessive current
    Could see that R233 and R226 showing signs of getting hot , compared to the others
    Tested ok so i decided to block change all transistors and drivers as i had them all
    All transistors tested ok, but i need to be sure
    Tested still the same, I found tryristor on the output socket board to be S/C
    Replaced that still the same, with the Tryristor removed i can power the channel up
    At this point i put the unit down for a few days

    On re testing this is what i have
    voltages on faulty channel are as follows all checked while on lamp limiter

    -35V on the output speaker socket

    peavey_xr8600_sch.pdf

    Q201 - B+97v C +35v E+97v
    Q202 - B+97v C +35v E+97v
    Q210 B +35v C+35v E+35v
    Q207 B +35v C+35v E+35v

    Q216 B +35V C-35v E +35v
    Q214 B +35V C-35v E +35v
    Q219 B - 97v C -35v E -97v
    Q220 B - 97v C -35v E -97v

    Q200 B +27 C +97v E +35v
    Q208 +35 all pins
    Q221 B - 35v C-97v E -35v
    Q215 B -35v all pins


    R 252 but has got burnt,, still ok ,but replaced it anyway
    15+ /15- present and 25V +/-
    as stated before all the output transistors and 4 drivers ( all of the above ) been changed for new and like for like
    all have been checked that they are ok and correct and in the right positions

    I would really appreciate any help on this one

    Many thanks in adavnce
    MR A





  • #2
    Please provide static Vdc on the following:
    Q 209 & Q 212
    Q 206 & Q 217.
    E B C

    Comment


    • #3
      Thank again I will try and do it tomorrow. Thanks

      Comment


      • #4
        Red flags:

        Q200 B +27 C +97v E +35v
        Normal Vbe is around +/- 0.65V depending on being NPN/PNP
        Opposite polarity and crazy 8V difference points to a major problem.
        For more precision measure straight Vbe, not from each to ground.

        Q208 +35 all pins
        Q215 B -35v all pins
        Fully shorted?
        Measure diode drop from each pin to each other, all ways, with amp OFF and caps fully discharged.

        Side note in case you didnīt consider it: amp is "grounded output flying rails" type, speaker out comes from main caps center tap which is "close to ground but not real ground".
        You might find different voltage rails and wonder where that may come from.




        Juan Manuel Fahey

        Comment


        • #5
          Morning again
          Ok before i get on with my other daily work
          I will post this

          Q209 C=0.8v B=8.4v E=0.7
          Q212 C =0.7v B = 0.7 E= -14v
          Q206 C = 27v B = 2.4v E =1.8v
          Q217 C = 1.8v B 9.4v E = -27v
          All measured from (GND A)
          Again i have checked all the transistors that i have changed all test ok and all correct. apart from changing power transistors and the 4 drivers i have done nothing else

          thanks for your help i'm losing the will to live on this one

          Comment


          • #6
            Q 209 & Q 212 Emitters are shown as at ground potential.
            How can there be a voltage on them?

            Comment


            • #7
              More red flgs:
              Originally posted by Arbutt View Post
              Q209 C=0.8v B=8.4v E=0.7
              Q212 C =0.7v B = 0.7 E= -14v
              Q206 C = 27v B = 2.4v E =1.8v <--- only normal value
              Q217 C = 1.8v B 9.4v E = -27v
              All measured from (GND A)
              Juan Manuel Fahey

              Comment


              • #8
                Thanks jm fahay. I'm sadly out of my depth on this one. Do you have any pointers on what to look at next.

                Comment


                • #9
                  Originally posted by J M Fahey View Post
                  Side note in case you didnīt consider it: amp is "grounded output flying rails" type, speaker out comes from main caps center tap which is "close to ground but not real ground".
                  You might find different voltage rails and wonder where that may come from.
                  Originally posted by Jazz P Bass View Post
                  Q 209 & Q 212 Emitters are shown as at ground potential.
                  How can there be a voltage on them?
                  Maybe using the wrong point as ground reference?

                  "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                  Comment


                  • #10
                    Thank you g1. I have measured the q212 and 209 from Gnd-a reference. Is that the correct reference gnd point? I have a working channel to refer too.

                    Comment


                    • #11
                      GndA reference should be ok. But there can be a bad connection between GndA and GndDR.
                      Check that good side Q109 & Q112 emitters are at 0VDC.

                      Check resistance from Q209 emitter to GndA. Compare to resistance reading from Q109 emitter to GndA.
                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                      Comment


                      • #12
                        Originally posted by g1 View Post
                        GndA reference should be ok. But there can be a bad connection between GndA and GndDR.
                        Check that good side Q109 & Q112 emitters are at 0VDC.

                        Check resistance from Q209 emitter to GndA. Compare to resistance reading from Q109 emitter to GndA.
                        Measuring the grounds with power off
                        Between GND A and GND DL i have 144 ohms on both channels ( Page one has them connected with 150R ( R273 )
                        working channel at jnc of zd103/zd102 = 0v

                        Measured from gnd A and on lamp limiter

                        faulty channel has 1.21v at jnc of zd202 /203
                        anode of zd203 -13,5v
                        cathode of zd202 1.93v
                        R252 burning up with -13,5v and -59v on it

                        i will come back to this a little later





                        Comment


                        • #13
                          Morning all
                          I'm stuck indoor self isolating after catching covid19. Can't get to my workshop, so i thought i would ask if anyone can shed some light on whats going on, with the info i have supplied , before i cut my loses and hand it back
                          many thanks
                          Arbutt

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