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Fender M-80 Bass Schematic

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  • Fender M-80 Bass Schematic

    Hi,
    Just signed up and am currently working on a M-80 Bass Amp. I see there is lots of discussion on it. Just wondering if anyone has a Schematic for it.
    Thanks

  • #2
    http://www.mif.pg.gda.pl/homepages/tom/files/FenM80.gif

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    • #3
      m-80 bass schematic

      Thanks for the schematic - Teemuk
      Dan

      Comment


      • #4
        Fender M-80 Bass Schematic?

        Hi,
        The schematic I recieved is not correct.
        My model is Fender "M-80 Bass"
        PR 178
        Ser# LO-494616

        Does anyone have any other schematics specific to this model?

        Thanks,
        Dan

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        • #5
          Fender has ordering information here: http://www.fender.com/support/manuals/manuals.php and it looks like the four different M-80 products would be $5.00 each if no one here has one in their archive...

          Eric.

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          • #6
            WHO sent you the wrong one? And did you ask specifically for the M80 Bass? As ice says, there are several M80 amps.
            Attached Files
            Education is what you're left with after you have forgotten what you have learned.

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            • #7
              Here's one to revision B:
              http://www.mif.pg.gda.pl/homepages/tom/files/FenM80.gif

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              • #8
                M-80 Bass Schematic Pwr Section

                Hi Guys,
                the schematic i received has a different power section than what is actually on the board.
                According to the schematic CR49 & CR50 are Zerners - controlling the +16V and -16V.
                On the board are 2 regular IN5402's diodes.
                Now as far as the voltages I have only +6.6V (on CR49) and -16V (on CR50).
                I susspect this is the problem, since I need +16.

                Any Ideas?

                Thanks,
                Dan

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                • #9
                  Thats weird...I thought all the M-80's used zeners.
                  I would double check them .. one end should connect to a large oblong
                  whiteish wire wound resistor 5 watts or 7 watts 270ohms or in some guitar amps 330 ohms.
                  In fact there was a fender tech bulletin for the bass amp in '93
                  M-80 Bass Power Supply Modofications
                  A resistor change is required in the power supply section to reduce the amount of current through the 16 volt zener diodes CR49 & CR50. This will minimise the possibilty of the zeners overheating.
                  Remove R144 & R145 (270 ohm, 7W), and replace them with 390 ohm, 7W wire wound resistors. Make sure to glue the resistors to the p.c. board using an RTV silicone compound.
                  Last edited by oc disorder; 03-27-2009, 03:24 AM.

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                  • #10
                    They say 1N5402 right on them? Right nexst to each other in the middle along the edge of the board? They are 5 watt zeners, so they look like 3A rectifiers. But they should be 1N5353. Change the one that reads 6 volts, they should show 16v.
                    Education is what you're left with after you have forgotten what you have learned.

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                    • #11
                      Fender M-80 Diodes/Zerners

                      Hi guys,

                      OK I think I finally got to the bottom of this. The other Night I only removed CR49 and it was the IN5402. Which did not match the schematic. I SHOULD have removed CR50 - never assume! Of course CR50 was correct (IN5353B). Then I pulled out CR35 - it had some obscure diode in there so I put the IN5402 from CR49. I will get another IN5353B tomorrow and put it all back together.
                      I have no idea where this guy had this thing serviced - but they really screwed it up.
                      I will keep you posted on how it sounds after this.

                      Thanks,
                      Dan

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