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Randal RG200 G3 fix help?

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  • Randal RG200 G3 fix help?

    I have problem with huge heat and 3 cement resistor have fallen from the board (probably from heat are burned). I replaced that 3 cement resistors and 2 two suspicious MOFSET. Now i have bass frequency noise independently of the master volume potentiometer. If i remove 3 replaced resistors (in that case amp work without 2 mofset), amp work nice but again with a huge heating. I see that one ceramic capatitor (i think it is mofset bypass) is missing, and i dont know if it is really missing on this schematic, or in this revision is omitted. I doubt that it creates a problem, I do not know what other could do. Any hint or help?

    EDIT: i found scheme on forum but i think its other revision, and i see totally different values. i need "RANDALL G300PAP REV1.0 04/06/06" scheme
    Last edited by hall; 06-04-2012, 06:49 PM.

  • #2
    no one reply...but anyway i solved problem myself. As I said, i replaced 3 cement resistors (one is behind the cables), one metalfilm resistor, two transistors that gave strange value measurement and two main caps (8200uf/80V) on power regulation... amp now work like a charm.

    here are some pics:
    Click image for larger version

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    old buldged caps and old transistors


    Click image for larger version

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    ...and, how it looks now
    edit: Also changed two smaller capacitors (47uF/450V) behind these two bigger showed on picture, they were for preamp section (pream tube)...looks ok, but they are also su'scon brand, so I replaced them just in case.

    Click image for larger version

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    amp img - shows what I changed

    I would recommend for all users of this amplifier to replace the capacitors on the power supply because they are poor quality. Su'scon and Samxon in my experience have proved that these brands are extreme poorly known brands that are all lumped into all electronics with intent to occurs failure and buy new device again

    cheers

    sorry for my bad english.
    Last edited by hall; 06-05-2012, 07:58 PM.

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