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Mackie SRM450 v2 repair

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  • Mackie SRM450 v2 repair

    Hello everyone,

    I recently saved a Mackie SRM450v2 from the dumpster and it's in quite good condition, but there are two fried resistors. R245 and R243 have been damaged beyond recognition. I have the service manual, but the values in there seemed a bit on the low side, so I was already doubtful about simply replacing them.(20kOhm & 47r5Ohm respectively, @ 1W)

    Somewhere on this forum, there was another thread where these two resistors are mentioned, but no specific values, alas. It did mention something about the values in the manual being too low. I also found a repair-video on youtube, where I got a better (not good) look at the pair and the values for those were, if I read them right, 100kOhm and 47kOhm respectively .

    All this has left me quite confused and so I turn here, in the hopes that anyone can tell me the right values.

    many thanks in advance,

    Henri

  • #2
    Hello Henri

    Good form is to post or link the schematic so we can have some idea what we are working with.
    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
      Hello Henri

      Good form is to post or link the schematic so we can have some idea what we are working with.
      Hello Enzo,

      I will post the schematics when I get home from work! Thanks for making me aware.

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      • #4
        Silly me; I was looking at the schematics of the v1.

        I found the v2 schematics and after a bit of searching, I found the values for the two resistors.
        for some reason I wasn't able to upload the entire manual, or anything else; I keep getting an error-message that says
        I'm not authorized to create or remove attachments.

        I'm still wondering though, about the W's for these, because I read that they can heat up quite easily and burn through.
        any thoughts on that?

        greetings,

        Henri

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        • #5
          Just FYI, you can buy a third-party replacement backplate amp for SRM450v1/2 for about $150. It's good. I installed one for a client.
          --
          I build and repair guitar amps
          http://amps.monkeymatic.com

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          • #6
            this is a link to an image of the two resistors and a screenshot I grabbed from the schematics
            https://imgur.com/a/fnDGZqv
            Last edited by F_H_D; 08-20-2020, 05:53 PM.

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            • #7
              Originally posted by xtian View Post
              Just FYI, you can buy a third-party replacement backplate amp for SRM450v1/2 for about $150. It's good. I installed one for a client.

              as I stated earlier, the rest of the board seems fine, so for the time being there's no need for that and of course, I hope it won't be necessary at all.
              15 euro vs. 150 euro is still a big bite out of my budget. but thanks for the tip!

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              • #8
                I also noticed that R288, which is just next to R245 in the photo (to it's left side) is marked down for 100KΩ in the schematics, while the guy in the image has a 200KΩ in there.
                https://imgur.com/a/fnDGZqv

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                • #9
                  found the answers to my questions!!
                  https://imgur.com/tjVWT6B

                  thanks for responding anyhow!

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