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KRK Rokit 8 (G3?) -19v on the mute pin - Anyone have an older schematic?

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  • KRK Rokit 8 (G3?) -19v on the mute pin - Anyone have an older schematic?

    Hi All,

    I have a Rokit 8 that was blowing it's main fuse, I found a short in the diode bridge for the tweeter side of the circuit, I changed all the diodes for new ones. This solved the problem fuse blowing, but on testing i found the TDA2052 was putting +3.4v on the Output pin. I've removed the TDA2052 and found the mute pin 3 is being supplied with - 19v, which can't be right. For good measure, I've removed loads of the black gunk, there is a mix of soft clear silicone and hard to remove rock hard back crap.

    The correct schematic would be helpful, the only one I've found is for a newer and different board lay out. This board is dated 2013, Version A1.

    Thanks!

  • #2
    The 'Mute' circuit is the same as the main output mute.
    To unmute the TDA2052, Pin #3 must be +2.7 V above -V rail for the IC.
    That + voltage appears to come from an opamp before the header (preamp board?)
    Rockit TDA2052 Circuit.pdf
    RP8G2 AMP sch.pdf

    Comment


    • #3
      Thanks for those, I'd seen the first pdf, but not the second.

      The board in this particular model is all in one, that is there is no separate preamp board. The only separate boards are for the DI/Balance and a 3 pin 5V standby circuit mounted behind the IEC mains input. There is no 9 pin header (CN4) anywhere. I'll check the op-amps and see if any have suspect readings.

      Comment


      • #4
        If you remove the black gunk that has gone electrically conductive, replace the corroded components, (in the worst cases) and it should function again.
        They all suffer from this built in obsolescence.
        Support for Fender, Marshall, Mesa, VOX and many more. https://jonsnell.co.uk

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        • #5
          Originally posted by Jon Snell View Post
          If you remove the black gunk that has gone electrically conductive, replace the corroded components, (in the worst cases) and it should function again.
          They all suffer from this built in obsolescence.

          Hi Jon, I've removed all but a small area of the black gunk, mainly because it's bonded to/around some of the interconnecting plug sockets, I don't want to break them if possible as I had a helluva job getting the plugs out in the first place due to the slathering of the black stuff in and around it. I only found one slightly corroded part under some of the black stuff, that was a 222 SMD resistor. I've cleaned it up, removed all gunk around it and checked it over, the resistor is fine and the circuit is connected to both sides, it's just a little discolored. The majority of this device has clear silicone holding the caps in place on the main board.

          Click image for larger version

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          You can see the 222 center left. Removing the gunk took a little of the solder mask with it

          I took a reading on the mute pin hole with the standby removed, it drops to -1.7v, reconnecting the standby see it's shoot back up to -19v. The actual separate standby module is putting out 5v correctly.

          Comment


          • #6
            I've done some further tinkering today, Jazz P Bass mentioned an opamp used in the mute circuit, so I looked at those for anything odd. One of the TL074C's is putting out -10v on outputs 3 and 4, it's near the mute circuit, although might not be part of it. I've also noticed there is a unmarked SMD 8 pin IC in the area of the mute/standby circuit, when probed it will change the voltage found at the TDA2052 mute pin, from -19v to -13v, this coincides with a nearby Zener diode that feeds part of the mute pin circuit (as far as i can tell looking at the traces) switching from a -v output to a +6v output.

            Comment


            • #7
              Just to update this thread and close it off, I ended up buying a complete spare part for the unit, which unfortunately included everything apart from the driver and cabinet , but that still worked out cheaper than a complete new unit, so it could be worse. The new spare part has a different design to the original and no longer has the TDA2052, the board is labeled as a Version 2.

              Comment

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