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Thread: Broken EDC SR-99 drum machine

  1. #1
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    Broken EDC SR-99 drum machine

    Hi.

    Flushed with success from my boss dr-55 fix (see other thread), I decided to have a go at my broken EDC SR-99 drum machine.
    This is different to both the dr-55 and sr-88 machines, so the schematics aren't that much use. (the '99 is more complex)

    The problem is that I can't get the damned thing to go into 'pattern write' mode. It stays in "play" mode, and the start/stop buttons just do exactly that, not program sounds.
    I have replaced the 4011 (although it's socketed and the socket may be dodgy -someone else did that..) and also the TC5514 memory chip. No luck.

    I cannot find a schematic or service manual for the sr-99 anywhere.. can anyone help, or point me in the right direction?

    Thanks.

  2. #2
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    Here's a link to my blog about this project: https://synteknik.com/projects/curre...sr-99-project/

  3. #3
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    Where do the sounds come from and why are they not there? When the unit was brand new you could play sounds without programming couldn't you?
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    The patterns are stored in the SRAM chip. They get wiped if the battery is disconnected, and/or you replace the chip, which I have.

  5. #5
    g1
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    Sorry, I misunderstood and thought you meant it doesn't play or write.
    So it will play the factory sounds, but won't go into 'pattern write' mode?
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  6. #6
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    That seems to be the problem, yes.
    Sorry about the delay, I got distracted by another shiny project (Hohner EK 2)

  7. #7
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    Attached is a 5514 datasheet. Check for any action on the read/write pin when you activate pattern write button (and I hope you have verified the button switch).
    If no action on the R/W pin, trace back from it and see where it is getting that command from.
    I don't have high hopes for this unit without a schematic.
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