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Roland kc-550, no output?

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  • #16
    BigCJ- Welcome to the place. As Jazz mentioned, that is a really common part and is available from lots of sources.

    You didn't mention why you need one. Do you have an amp that has the same burned resistor or is it just the fact that there is no output?

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    • #17
      Yes, I have the same problem. No output or blown fuse and R41 decaded.

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      • #18
        Originally posted by Jazz P Bass View Post
        Show nuff, it's the zobel.
        Replace the caps.
        Check the bases of the ouput transistors to see if voltages are correct.
        The outputs should barely be turned on at idle.
        I would scope the output, looking for oscillation.
        That may be where the power is going.
        I know I am digging this up from the dead, but I am in need of the Roland KC-550 schematic and the attached file Jazz P Bass posted above (Roland_kc-350_kc-550.pdf) seems to be no longer available. Anyone have an archived copy of this somewhere? I can't find it anywhere on the 'net at the moment. Maybe Roland got wind of the file out here and doesn't like it?

        Also, great forum! I wish I had found this place a few years ago. I have a few pieces of gear I need to fix...
        joe vitek
        Melbourne, Fla

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        • #19
          ROLAND KC-350 KC-550 Service Manual free download, schematics, eeprom, repair info for electronics

          At the bottom of the page, where it says 'need progs', that will change to 'download file' after a short period.

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          • #20
            Thanks John, however, this never changed for me. The screen shot below is what I get (file not found). Were you able to go to this link recently and get the file again?
            Click image for larger version

Name:	roland_kc550_not_found.png
Views:	1
Size:	131.7 KB
ID:	832091
            Could you email me that file if you have it? joe.vitek [aaht] l-3com.com. Thanks again!
            joe vitek
            Melbourne, Fla

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            • #21
              Appears to have been removed from elektrotanya.
              Try the one on this page:
              http://music-electronics-forum.com/t34745/

              edit: if you can, please unzip and repost attachment to this thread
              Originally posted by Enzo
              I have a sign in my shop that says, "Never think up reasons not to check something."


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              • #22
                Thanks Greg! That's it! However, I couldn't attach it. It is slighty too big. I got this error when I tried to upload it:

                "The following errors occurred:
                Roland_kc-350_kc-550 copy.pdf: Your file of 4.89 MB bytes exceeds the forum's limit of 4.77 MB for this filetype."

                Doh, just an RCH over the size limit...
                joe vitek
                Melbourne, Fla

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                • #23
                  That would explain why it was posted as zip, thanks for trying!
                  Originally posted by Enzo
                  I have a sign in my shop that says, "Never think up reasons not to check something."


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                  • #24
                    Here it is as the zip reposted here:
                    Roland_kc-350_kc-550 copy.zip
                    joe vitek
                    Melbourne, Fla

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                    • #25
                      Do you know the specs of C26 & C27? My C26 exploded and burned the R41 and C27 and toasted my speaker too. Trying to fix it myself but can't find specs on those. Desperate for help...

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                      • #26
                        The schematic posted above says .068UF.
                        "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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                        • #27
                          replacing a busted a cap

                          Thanks!! I just ordered a film capacitor that meets the specs. Fingers crossed that it will work. I also ordered a pack of 'flame proof' resistors to replace the R41. Here's a link to the caps I just bought :

                          https://www.westfloridacomponents.co...apacitors.html

                          here's the link to the super resistors:

                          27 Ohm 1/2W Flameproof Resistor 10 Pcs.

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                          • #28
                            Why?

                            I see someone here also has a blown R41 and/or blown C26&27. Why did this happen? Is this particular failure common? I don't know much about electronics aside from soldering, I ordered the new components but I'm worried that they are going to immediately blow again after I replace them, is that likely? I'm nervous about this. I hope my amp just magically doesn't have any problems once I replace the parts...

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                            • #29
                              The components that 'blew' are of the circuit type labeled "Zobel Network'.

                              If one of the capacitors just so happened to 'go short', then that is what took them out.

                              OR, the output section itself is damaged & 'took' the Zobel out.

                              For test purposes, the amp should run without the network.

                              If you want to check the output section, the briefest test would be to hook up a volt meter to the output jacks.(no speaker)
                              Set the meter to read Volts/ DC.
                              If you get a very low (millivolts) reading, it is a good indication that the output is o/k.

                              There are much more indepth tests that can be applied, but this one will suffice for a start.

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                              • #30
                                I'll add: (and this is mostly my opinion based on experience and not necessarily fact)

                                The voltage rating of cheap caps needs to be de-rated at higher frequencies. I don't necessarily trust the rating in a Zobel Network. If it were me, I would have probably ordered higher voltage rated caps for piece of mind and not looked back. Usually when I've seen this happen, it's because the caps were poor quality and under-rated in the first place.
                                "I took a photo of my ohm meter... It didn't help." Enzo 8/20/22

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