35v DC at speaker terminal!

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • onejay09
    Senior Member
    • Nov 2011
    • 67

    #1

    35v DC at speaker terminal!

    hi guys im trying to repair my active subwoofer its an expensive piece of kit. so id rather fix it than bin it. its a monitor audio vw8 active sub its a push pull ab amplifier board, ive got the scematics here ill post below, ive already repaired this once before:

    https://www.badcaps.net/forum/showthread.php?t=32471

    this time as the title sudgests ive got 35 volts at the speaker terminal!,
    im not smart enough to say whether this has an output thats capacitor coupled..

    the speaker hums like 60hz or 120hz, theres no input and the volume doesnt change the sound atall. i unplugged the pre amp section and the hum doesnt stop.

    transformer is centre tapped ground but it seems ok
    outputs are tip35c/tip36c, they seem ok too
    driver transistors seem ok
    filter caps were replaced theyre ok
    bridge rectifier is new also

    shouldnt the protection relay prevent this?
    What am i Missing? any help would greatly bee appreciated, thanks for reading guys
    Last edited by onejay09; 08-26-2014, 07:06 AM.
  • onejay09
    Senior Member
    • Nov 2011
    • 67

    #2
    Re: 35v DC at speaker terminal!

    power amp stage

    Comment

    • onejay09
      Senior Member
      • Nov 2011
      • 67

      #3
      Re: 35v DC at speaker terminal!

      power supply

      Comment

      • stj
        Great Sage 齊天大聖
        • Dec 2009
        • 30994
        • Albion

        #4
        Re: 35v DC at speaker terminal!

        check Q512 & Q513 for shorts.

        the hum would be c901 & c902

        Comment

        • stj
          Great Sage 齊天大聖
          • Dec 2009
          • 30994
          • Albion

          #5
          Re: 35v DC at speaker terminal!

          oh - i see you did that stuff!

          Comment

          • onejay09
            Senior Member
            • Nov 2011
            • 67

            #6
            Re: 35v DC at speaker terminal!

            yes i checked the outputs off the board for shorts, none.
            q508 q509 q510 q511 seemed to be ok, but when onboard q511 reads both ways from leg 1 to 3 which is a 2sb647. -neg to pin1 +pos to pin3 .874 other way around is .709

            Comment

            • onejay09
              Senior Member
              • Nov 2011
              • 67

              #7
              Re: 35v DC at speaker terminal!

              its almost like the outputs are allways on

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: 35v DC at speaker terminal!

                " but when onboard q511 reads both ways from leg 1 to 3 which is a 2sb647" That is because you are reading the PN junction of Q513. What DC Voltage do you get at E-B of Q513? Right now more likely that the bottom half (the negative) of the output is not on.
                Since you did the repair work on it before, did you verify the soldering works that was done last time?
                Last edited by budm; 08-26-2014, 09:29 AM.
                Never stop learning
                Basic LCD TV and Monitor troubleshooting guides.
                http://www.badcaps.net/forum/showthr...956#post305956

                Voltage Regulator (LDO) testing:
                http://www.badcaps.net/forum/showthr...999#post300999

                Inverter testing using old CFL:
                http://www.badcaps.net/forum/showthr...er+testing+cfl

                Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                http://s807.photobucket.com/user/budm/library/

                TV Factory reset codes listing:
                http://www.badcaps.net/forum/showthread.php?t=24809

                Comment

                • onejay09
                  Senior Member
                  • Nov 2011
                  • 67

                  #9
                  Re: 35v DC at speaker terminal!

                  Hi budm! Glad your here, you helped greatly last time,
                  Yes the soldering was fine I even increased the copper traces with solder to make good.

                  I'll check in about an hour when I'm home
                  Thanks

                  Comment

                  • onejay09
                    Senior Member
                    • Nov 2011
                    • 67

                    #10
                    Re: 35v DC at speaker terminal!

                    from pin 1 to 3 q512 read .345 volts, and q513 it read .485 vdc

                    both outputs are 1base 2collector 3emitter.

                    Comment

                    • onejay09
                      Senior Member
                      • Nov 2011
                      • 67

                      #11
                      Re: 35v DC at speaker terminal!

                      ive heard of outputs being capacitor coupled? would that put this much dc on the output?

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: 35v DC at speaker terminal!

                        This direct couple output amplifier and there is speaker protection relay to disconnect the output of the amplifier from the speaker so when you have DC VOLTAGE (>2V) it will not damage the speaker. You should not see any DC voltage at the speaker terminal right now since the relay should be OFF at this point.
                        Q512 (the top positive drive) has less bias than the bottom negative drive Q513, which should have made the output have more negative DC than the positive DC at the output.
                        Is it 35V plus or minus voltage at the output? Polarity indication needed for that voltage reading
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment

                        • onejay09
                          Senior Member
                          • Nov 2011
                          • 67

                          #13
                          Re: 35v DC at speaker terminal!

                          theres definatley dc at the speaker terminal. when i turn it off the relay clicks off and the voltage drops to 0

                          so black dmm lead to negative speaker terminal red to positive = -28.5v dc

                          Comment

                          • onejay09
                            Senior Member
                            • Nov 2011
                            • 67

                            #14
                            Re: 35v DC at speaker terminal!

                            is r518 the bias resistor or r519/r520?

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: 35v DC at speaker terminal!

                              1) One thing bad right now is that the protection circuit is not working because you do have voltage at the speaker terminals, the protection relay should stops that voltage from getting to the speaker terminals.

                              2) I know you have DC voltage at the out but I do not know if it is positive voltage or negative voltage since this amplifier uses bi-polar power supply (it has + and - voltage with ref to the circuit ground). So now I know that the output is negative 28.5V which correspond to the Bias voltage reading on the two output transistors Q512 (POSITVE DRIVE) which has less bias than Q513 (NEGATIVE DRIVE). In simple terms, the the output is not balanced, you have more negative drive than the positive drive, if both are equal, the output will then be 0V.
                              So we need to find out next why the positive drive Q512 has low bias than normal.
                              Q507 is an active bias circuit for the output section.
                              You should check everything in those section at least.
                              Attached Files
                              Last edited by budm; 08-26-2014, 04:11 PM.
                              Never stop learning
                              Basic LCD TV and Monitor troubleshooting guides.
                              http://www.badcaps.net/forum/showthr...956#post305956

                              Voltage Regulator (LDO) testing:
                              http://www.badcaps.net/forum/showthr...999#post300999

                              Inverter testing using old CFL:
                              http://www.badcaps.net/forum/showthr...er+testing+cfl

                              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                              http://s807.photobucket.com/user/budm/library/

                              TV Factory reset codes listing:
                              http://www.badcaps.net/forum/showthread.php?t=24809

                              Comment

                              • onejay09
                                Senior Member
                                • Nov 2011
                                • 67

                                #16
                                Re: 35v DC at speaker terminal!

                                the negative speaker terminal is on the same trace for center tapped ground from the transformer.. if that helps
                                Last edited by onejay09; 08-26-2014, 04:09 PM.

                                Comment

                                • onejay09
                                  Senior Member
                                  • Nov 2011
                                  • 67

                                  #17
                                  Re: 35v DC at speaker terminal!

                                  so its like one of the outputs are stuck on?

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: 35v DC at speaker terminal!

                                    One is not turned on (bias on) enough to balance out the output to 0V. see updated post 15.
                                    "the negative speaker terminal is on the same trace for center tapped ground from the transformer" That is correct connection and that is how it should be.
                                    Never stop learning
                                    Basic LCD TV and Monitor troubleshooting guides.
                                    http://www.badcaps.net/forum/showthr...956#post305956

                                    Voltage Regulator (LDO) testing:
                                    http://www.badcaps.net/forum/showthr...999#post300999

                                    Inverter testing using old CFL:
                                    http://www.badcaps.net/forum/showthr...er+testing+cfl

                                    Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                    http://s807.photobucket.com/user/budm/library/

                                    TV Factory reset codes listing:
                                    http://www.badcaps.net/forum/showthread.php?t=24809

                                    Comment

                                    • onejay09
                                      Senior Member
                                      • Nov 2011
                                      • 67

                                      #19
                                      Re: 35v DC at speaker terminal!

                                      q508 q509 q510 q511 were replaced the last time i repaired it, could a resistor fall out of value?

                                      had another look at post 15
                                      how do we find the issue, ive had q508 q509 q510 q511 off the board and tested, no shorts but im unsure if they are leaky or failing, they read at most .78 nothing higher
                                      Last edited by onejay09; 08-26-2014, 04:17 PM.

                                      Comment

                                      • onejay09
                                        Senior Member
                                        • Nov 2011
                                        • 67

                                        #20
                                        Re: 35v DC at speaker terminal!

                                        q507 "mpsa13" seemed a little high at .86 on some readings

                                        Comment

                                        Related Topics

                                        Collapse

                                        • falkikowski
                                          NuPro A-20 Active Speaker burnt LNK 606
                                          by falkikowski
                                          Hi,
                                          The LNK 606 on the power board for my active speaker just went to hell.
                                          I would like to replace it, but this very model is hard for me to get. Can I replace the LNK 606 with the LNK 616 or the TYN 266?

                                          I also attached a picture of the back side. The burnt part above R2 is a bridge, that is connected to the COM of two chunky electrolytic condensator (82 micro Farad, 400 V). I just tidied that up. Or should I worry about that?

                                          Thanks​
                                          falkikowski...
                                          10-03-2024, 03:09 AM
                                        • Document Archive
                                          HP ProDesk 600 G5 + Bluetooth Speaker 400 ProDesk 600 i7-9700 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP ProDesk 600 G5 + Bluetooth Speaker 400 can be useful for upgrading or repairing a desktop PC that is not working. As a community we are working through our specifications to add valuable data like the ProDesk 600 G5 + Bluetooth Speaker 400 boardview and ProDesk 600 G5 + Bluetooth Speaker 400 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer...
                                          09-12-2024, 02:30 PM
                                        • Document Archive
                                          HP EliteBook 830 G6 + Bluetooth Speaker 400 Notebook 800 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP EliteBook 830 G6 + Bluetooth Speaker 400 Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the 830 G6 + Bluetooth Speaker 400 boardview and 830 G6 + Bluetooth Speaker 400 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties...
                                          09-06-2024, 06:00 PM
                                        • Document Archive
                                          HP EliteBook 840 G6 + Bluetooth Speaker 400 Notebook 800 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP EliteBook 840 G6 + Bluetooth Speaker 400 Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the 840 G6 + Bluetooth Speaker 400 boardview and 840 G6 + Bluetooth Speaker 400 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties...
                                          09-06-2024, 06:00 PM
                                        • Document Archive
                                          HP EliteBook 840 G6 + Bluetooth Speaker 400 Notebook 800 Specification for Upgrade or Repair
                                          by Document Archive
                                          This specification for the HP EliteBook 840 G6 + Bluetooth Speaker 400 Notebook can be useful for upgrading or repairing a laptop that is not working. As a community we are working through our specifications to add valuable data like the 840 G6 + Bluetooth Speaker 400 boardview and 840 G6 + Bluetooth Speaker 400 schematic. Our users have donated over 1 million documents which are being added to the site. This page will be updated soon with additional information. Alternatively you can request additional help from our users directly on the relevant badcaps forum. Please note that we offer no warranties...
                                          09-06-2024, 06:00 PM
                                        • Loading...
                                        • No more items.
                                        Working...