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Mesa 2:90 woes _ tubes not coming on

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  • Mesa 2:90 woes _ tubes not coming on

    So I've had a problem with my Mesa, the other day it was working ok but today switched in and no sound. Checked the fuses and they look fine, the tubes on the other hand were off, no glow or heat. I was slightly concerned about the fuses in the back, on the panel it specifically says use 1A and the fuses installed are 3A. I'm worried something more serious has blown down the line... anyway I'm really hoping that it can be fixed, any help or advice is greatly appreciated, thanks in advance.

  • #2
    No heaters means they are not getting power supply. SO find out where it went.
    Education is what you're left with after you have forgotten what you have learned.

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    • #3
      Originally posted by Enzo View Post
      No heaters means they are not getting power supply. SO find out where it went.
      I'm really not sure how to find this - I took the lid off and checked inside - there's power to the fan but that's all I'm able to discern by looking at it. Perhaps need to change the tube fuses anyway....

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      • #4
        Check heater voltage at tube sockets (should be around 6VAC). If missing, take out fuses and check for zero resistance. Don't go by looks.
        Last edited by Helmholtz; 06-30-2020, 01:26 PM.
        - Own Opinions Only -

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        • #5
          I don't see any internal fuses on the schematic (see attached), but I don't trust Mesa schematics either.
          Attached Files
          "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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          • #6
            If your 2:90 has a comb type multipin connector on the power supply board, with a gaggle of flying leads to the tube boards, it's possible the filament pins on that connector have oxidized due to being heated from all the current they have to carry. It's a common problem on a lot of their combos & heads after they went to this type of connector. If you find that to be the case, I don't think there's much point in cleaning up the pins on the board, and sometimes the electrodes in the multipin connector are burnt beyond repair anyway. In these cases, I run a pair of heavy gauge wires directly between the boards, scraping enough of the board coating off the lands so I can get a reliable connection. Luckily the filament pins are the only ones I've found to have this kind of problem - the remainder can safely be left in place.
            Enjoy. Every. Sandwich.

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            • #7
              Originally posted by Leo_Gnardo View Post
              If your 2:90 has a comb type multipin connector on the power supply board, with a gaggle of flying leads to the tube boards, it's possible the filament pins on that connector have oxidized due to being heated from all the current they have to carry. It's a common problem on a lot of their combos & heads after they went to this type of connector. If you find that to be the case, I don't think there's much point in cleaning up the pins on the board, and sometimes the electrodes in the multipin connector are burnt beyond repair anyway. In these cases, I run a pair of heavy gauge wires directly between the boards, scraping enough of the board coating off the lands so I can get a reliable connection. Luckily the filament pins are the only ones I've found to have this kind of problem - the remainder can safely be left in place.
              Just in case, I posted a number of photos on the outside and insides of the Mesa Simulclass 2:90 at this post, thread #10: https://music-electronics-forum.com/...-repair/51907-
              Logic is an organized way of going wrong with confidence

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              • #8
                Originally posted by Leo_Gnardo View Post
                If your 2:90 has a comb type multipin connector on the power supply board, with a gaggle of flying leads to the tube boards, it's possible the filament pins on that connector have oxidized due to being heated from all the current they have to carry. It's a common problem on a lot of their combos & heads after they went to this type of connector. If you find that to be the case, I don't think there's much point in cleaning up the pins on the board, and sometimes the electrodes in the multipin connector are burnt beyond repair anyway. In these cases, I run a pair of heavy gauge wires directly between the boards, scraping enough of the board coating off the lands so I can get a reliable connection. Luckily the filament pins are the only ones I've found to have this kind of problem - the remainder can safely be left in place.
                Bingo! At glance it seems at least one of the pins is singed to a crisp. So I should bypass the burnt wire and leave the others?

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                • #9
                  Ensure you make good the two high current heater connections.
                  Why they use cheap and nasty connectors, I will never understand except it gives built in obsolescence.
                  Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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                  • #10
                    Originally posted by Yovan View Post

                    Bingo! At glance it seems at least one of the pins is singed to a crisp. So I should bypass the burnt wire and leave the others?
                    Yes, replace the burnt wire, also its mate. The remainder of the connections, I've never had a problem with those, so I recommend you go no further after replacing the filament supply wires.
                    Enjoy. Every. Sandwich.

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