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mesa boogie m2000 repair

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  • mesa boogie m2000 repair

    last week my m2000 bass amp stopped working. no sound at all to the speakers, Di output only hum with more weird noises

    mesa boogie has been kind enough to share schematics. after all is a discontinued product.... i've put in the attachments so you can reference if needed

    i started checking the tubes in another amplifier, they are still working

    so i took measurements of all the voltages coming from the psu. everything was spot on, apart the +15V rail which was reading 0V

    took out the 7815 regulator and tested in another circuit. working perfectly

    something else is causing the +15V rail to drop. the problem is there are so many IC and other components connected to the +15V rail so it makes hard to find where the problem is. i am tempted to replace all the ICs but maybe there is a better way to follow

    do you have any suggestion?

    thanks in advance
    Attached Files

  • #2
    My only suggestion for boogie is put in sockets -- for ICs and relays if there are any.

    If you are lucky, shorted part gets very hot, and might help you find it quicker.
    If the voltage stays on long enough, before the regulator shuts itself down...

    Yeah, these amps are a major time commitment to repair, there are few easy avenues to find a short, except yanking out the parts.
    And no factory sockets makes that pretty time consuming...

    However, after the sockets are installed, next time it's serviced, probably only takes 1/5th the time.

    So I suck air the first time, put in sockets, and the next time it's much faster.

    Comment


    • #3
      I would start by seeing if the 7815 is getting 20 some volts at it's input.

      If it is, check the 7815 output pin resistance reading to ground.
      It should read high enough (1K) to not load down the regulator.

      And make sure the regulator ground pin is indeed reaching ground.

      Comment


      • #4
        Also, a quick start would be to use your finger (carefully) to touch around things that connect to the +15. It's possible the shorted device will be hot. Again be careful not only for higher voltages inside the unit and that you don't burn you finger!
        "Yeah, well, you know, that's just, like, your opinion, man."

        Comment


        • #5
          thanks guys, i didn't think of "finger probing". i will try that and keep you posted on the results. thanks!

          Comment


          • #6
            I wondered about the low-cost non-contact laser IR thermometers for this kind of work. I've seen them on offer for 15 with a claimed accuracy of +/- 1.5 deg.C.

            Trouble is, if you have a short you won't get any output voltage from the regulator to warm anything up because the internal current overload protection will kill the output.

            Comment


            • #7
              It still needs to be shown that there is a voltage going into the regulator.

              Comment


              • #8
                alright, found a shorted capacitor from +15V to ground

                now - with amp powered off - no more continuity with multimeter between the two rails

                is there anything more you would recommend to check before i put the amp back?

                any critical component measuring / substitution?

                i ask this because this amp has been a real pita to take apart, and i would like to do everything possible to lower the chances of having to do the same thing again

                Comment


                • #9
                  You said you had tested the regulator in another circuit and found it to be good, so you should be done. A cap. failure like that is not usually caused by anything else.
                  "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

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                  • #10
                    alright, so i will put the amp back soon, keeping the fingers crossed that i won't find more problems later on. will keep you posted. thanks!

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                    • #11
                      very good! the amp has been fixed

                      it's been a bit of a nightmare, this model is not repair friendly at all!

                      thank you everybody, i'm so happy i fixed this!

                      Comment


                      • #12
                        Hello there! I'm from Brazil and it seems that I'm having the same problem.

                        1) No sound at all but unit is powered on;
                        2) +90V, -90V and other PSU outputs ok, except for the +15V rail at the "top board" (blue wire). It is reading 0V;
                        3) Inputs at 7915 and 7815 are ok (about -20V / +20V);
                        4) Both VR's are reaching ground (7915 pin 1 and 7815 pin 2);
                        5) Output at 7915 is OK;
                        6) Output at 7815 is NOT OK;
                        7) 7815 is getting hot and its output pin resistance to the ground is near 0!
                        8) I've changed the two 1000uF cap near VRs but problem persists.

                        Someone has a clue?
                        Last edited by heliogalvao; 08-19-2017, 09:26 PM.

                        Comment


                        • #13
                          seems like something on the +15v rail is shorted

                          in my case it was one of the small yellow axial capacitors, but could be an opamp or transistor as well

                          you should lift components on the +15v rail one by one, until you find the faulty one.

                          i would start with capacitors since they are simpler, just lift one leg and check if the +15v is coming up.

                          with the opamps you don't have to remove them completely, just lift the pin connected to +15v, if you are careful you can do this without damaging the opamp or the pcb

                          with a bit of patience i am sure you will find the problem. as always be careful with the high voltages

                          Comment


                          • #14
                            Beatnik, THANK YOU SO MUCH to reply me.

                            1) When you say "+15V rail", you mean, that I have to get the schematics and follow the +15V way and test the components?
                            2) Are OPAMP the small ICs, is that right?
                            3) About capacitors, you mean all of them, or just eletrolytics? Do I have to lift one leg even if it's a ceramic?
                            4) About "+15V coming up", you mean, do I have to lift a component, then power up and check if +15V is up?

                            Note about high voltages: I got a shock days ago. Power was off, I was talking to someone and put my hand under the PCB... ehhehehe

                            Comment


                            • #15
                              you have to remove components that are connected to +15v , one by one , every time you remove a component you power on the amp again and check the voltage, when +15v comes back then you have found the faulty component

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