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Roland CR - 8000 rhythm machine

Discussion in 'Troubleshooting and Repair' started by Swampy, Mar 20, 2012.

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  1. Swampy


    Mar 20, 2012
    Hey everyone,

    This is a vintage number, produced in the early 80's.

    I've troubleshooted the circuit problem to the tempo clock, or lack of. I can get a few odd percussion hits here and there if I push the buttons, but sequences will not start or stop, and both the bar and beat lights are illuminated (the bar led should activate on pattern start and flash every three beats (eg) , and beat light should flash every beat).

    The relevant service manual page number is 12, and located here

    I can see that the tempo clock is built from a square wave oscillation but I've probed around and not found anything of such. I've managed to verify the supply voltages are ok (+5 VDC and -15 VDC)

    Also, I don't really understand how varying the DC at the base of Q12 adjust the clock frequency?? There's a fundamental gap in my knowledge of this oscillation circuit (I generally work with amplifiers...and come across flip flops once in a blue moon) so if anyone out there can spill the beans that'd be massively appreciated.

  2. Swampy


    Mar 20, 2012
    Sweet as, all sussed. Q11 had shorted, only satan himself knows why.
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Congrats, glad you got it fixed. Sorry, I've had no experience with these things.
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