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  • #91
    Any time you have a burn leaving carbon in a high voltage circuit you must remove all the carbon, or you will have a path for the high voltage. That may be what is happening here as the cap has the high voltage and the hum balance pot is near ground potential.
    Any carbon should be thoroughly scraped away, or even better, cut out. You may have to cut or drill away a piece of the board, then rebuild the traces with wire.
    "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


    • #92
      Originally posted by g1 View Post
      Any time you have a burn leaving carbon in a high voltage circuit you must remove all the carbon, or you will have a path for the high voltage. That may be what is happening here as the cap has the high voltage and the hum balance pot is near ground potential.
      Any carbon should be thoroughly scraped away, or even better, cut out. You may have to cut or drill away a piece of the board, then rebuild the traces with wire.
      Removed R43 and will be removing epoxy from board shortly. Just noticing that one pin of hum balance pot has continuity with pin 1 of V1-V6 and the other hum balance pin has continuity with pin 5 of V1-V6. Searching around board to see if either hum balance pins have continuity with anything else and so far not finding anything. The third pin of hum balance has continuity with R52.

      Comment


      • #93
        Originally posted by ca7922303 View Post
        Just noticing that one pin of hum balance pot has continuity with pin 1 of V1-V6 and the other hum balance pin has continuity with pin 5 of V1-V6. Searching around board to see if either hum balance pins have continuity with anything else and so far not finding anything. The third pin of hum balance has continuity with R52.
        Maybe you are counting pins from the wrong side. Pin9 of preamp tubes should go to one side of hum pot, pins 4 & 5 should go to the other side of the pot.

        It is best to not use the term 'continuity' with electronics. Specify the actual resistance value instead. Or say 'short' if it is around 0 ohms, maybe up to 2 ohms.
        Continuity works ok in 'go/no go' wiring applications like automotive, but most meters will indicate continuity for anything between 0 and 40 ohms, or some meters as high as 200 ohms. In electronics, the difference between 0 and 40 ohms can be critical.
        "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


        • #94
          Originally posted by g1 View Post
          Maybe you are counting pins from the wrong side. Pin9 of preamp tubes should go to one side of hum pot, pins 4 & 5 should go to the other side of the pot.

          It is best to not use the term 'continuity' with electronics. Specify the actual resistance value instead. Or say 'short' if it is around 0 ohms, maybe up to 2 ohms.
          Continuity works ok in 'go/no go' wiring applications like automotive, but most meters will indicate continuity for anything between 0 and 40 ohms, or some meters as high as 200 ohms. In electronics, the difference between 0 and 40 ohms can be critical.
          Checked pins connecting him balance to preamp tubes V1-V6. Getting 0.00 ohms on all.

          Comment


          • #95
            Have you had V5 tube socket removed yet? One of the pictures shows a bit of discoloration from the underside.
            With such an odd problem it would be worth removing it and inspecting it and the board where it mounts.

            Click image for larger version

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            "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


            • #96
              Originally posted by g1 View Post
              Have you had V5 tube socket removed yet? One of the pictures shows a bit of discoloration from the underside.
              With such an odd problem it would be worth removing it and inspecting it and the board where it mounts.

              Click image for larger version

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              Yeah, I was noticing alot of soot under V-5 last night. I'll remove socket and forward photos asap. Thanks.

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              • #97
                Originally posted by g1 View Post
                Have you had V5 tube socket removed yet? One of the pictures shows a bit of discoloration from the underside.
                With such an odd problem it would be worth removing it and inspecting it and the board where it mounts.

                Click image for larger version

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                V-5

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                • #98
                  That's pretty bad. The trace that has the green scraped away goes to pins 4 & 5 I guess. The arc from pin1 to that trace is what is putting the high voltage DC on the heater circuit and hum pot. The burnt area between pin1 and that exposed part of that trace will have to be drilled or cut out. The trace will have to be insulated again with nail polish or something. Or cut back and replaced with wire. The socket should clean up as the arc was not between pins.
                  Clean the board and socket up as well as you can and post pics.
                  "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


                  • #99
                    Originally posted by g1 View Post
                    That's pretty bad. The trace that has the green scraped away goes to pins 4 & 5 I guess. The arc from pin1 to that trace is what is putting the high voltage DC on the heater circuit and hum pot. The burnt area between pin1 and that exposed part of that trace will have to be drilled or cut out. The trace will have to be insulated again with nail polish or something. Or cut back and replaced with wire. The socket should clean up as the arc was not between pins.
                    Clean the board and socket up as well as you can and post pics.
                    V-5

                    Comment


                    • You'll have to grind out that burnt (blackened) part of the circuit board. Burnt circuit board can be conductive. It also looks like the trace may be burnt open (check continuity with meter). You may have to add a jumper wire.
                      "Yeah, well, you know, that's just, like, your opinion, man."

                      Comment


                      • Yes the black carbon will need to be ground/cut/drilled out. Be careful not to cut into the traces on the other side of the board. Then some corona dope or brush on high voltage insulation over the repaired area and the damaged trace. Or grind out the damaged trace as well and run an insulated jumper wire across the break like
                        The Dude
                        Supporting Member
                        The Dude mentioned.
                        "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


                        • Originally posted by g1 View Post
                          Yes the black carbon will need to be ground/cut/drilled out. Be careful not to cut into the traces on the other side of the board. Then some corona dope or brush on high voltage insulation over the repaired area and the damaged trace. Or grind out the damaged trace as well and run an insulated jumper wire across the break like
                          The Dude
                          Supporting Member
                          The Dude mentioned.
                          How do you feel about epoxy over the burnt spot on the board like I did under R43 and a jumper wire?

                          Comment


                          • The carbon must be removed. It is like a resistor and offers a path for the arc to strike. Epoxy won't do anything about that resistive path.
                            If you mean, can you use epoxy instead of corona dope once the carbon is removed? Yes it should work.
                            But having corona dope will be handy as you will likely have to deal with arcing again if you are working on tube amps.
                            "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


                            • Originally posted by g1 View Post
                              The carbon must be removed. It is like a resistor and offers a path for the arc to strike. Epoxy won't do anything about that resistive path.
                              If you mean, can you use epoxy instead of corona dope once the carbon is removed? Yes it should work.
                              But having corona dope will be handy as you will likely have to deal with arcing again if you are working on tube amps.
                              Any way of knowing if what I've done under R43 is good or could it be part of the issue still with the hum balance?

                              Comment


                              • Originally posted by ca7922303 View Post

                                Any way of knowing if what I've done under R43 is good or could it be part of the issue still with the hum balance?
                                I think it is probably ok if it's not close to any other traces except it's own. Neither side is near ground potential like that heater trace is. There is not a big voltage difference between the 2 ends of R43 so it's not likely to arc over. If anything the carbon under it will be in parallel with R43 which would effectively reduce it's resistance value.
                                In any case it should not have anything to do with the hum balance pot issue.
                                "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

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