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Roland Cube distortion

Discussion in 'Electronic Repair' started by N Cook, Dec 10, 2007.

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  1. N Cook

    N Cook Guest

    On "octave bass" setting only , which of course is the one used.
    A sort of auto-wah effect at the flanger rate but with the effects controls
    turned to off position. Alternate peaks of a 200 Hz input signal are
    attenuated.
    Thats with the gain pot at about 60 percent but above 70 percent then a
    cross-over type distortion moves into the attenuated traces as well.
    No response to twizzle stick or ribbon connector movement,SM IC pushing etc.
    Not fully taken apart yet , but any ideas ?
     
  2. N Cook

    N Cook Guest

    Should have said Roland Cube 30. Looks now more like a no goer.
    Any known problems with the system of pots (nothing ohmically wrong) turning
    to 0 ohm to switch off digital effects?, the LED goes out but it is as
    though the micro doesn't know that.
    Good sine signals through both sides of dual opamps IC1 and IC2, distorted
    signal at both sides of same IC , IC3.
    +/-8V supplies to the opamps good and clean as is 3.3V rail for the
    following.
    Tracing signal back it seems to go to IC4 an AKM4552VT no data found but
    AKM4550VT is an Asahi ADC/DAC of same 0.65mm format 16 pin but slightly
    different pinning.
    Good sine in but distorted signal out so presumably the digital processing
    is buggered somehow.
    I doubt if a schematic would help if its a corrupt micro.
     
  3. N Cook

    N Cook Guest

    Looks like a pot problem
    Tracing the lines back to the 48 pin IC8 Roland chip then pin 22 goes to the
    LED and the wiper of the effects pot goes to pin 4 via 100R.I don't
    understand why with a few ohms left on the pot at "zero" the LED goes out
    but the effect does not stop. Rather than trying to change the sub miniature
    pot I'll add in a switch to ground on the pin4 side of the 100R, as the
    owner never uses the effects anyway.

    The crossover problem was not realising I was on the wrong sig gen
    attenuator setting.
     
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