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Roland KR-370 Main board

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    Roland KR-370 Main board

    Just finished refreshing this board. I had to replace all the SMD electrolytic caps, they were all bad and leaked on the board, so also had a lot of work restoring destroyed pads/vias/traces. Not even sure if it works in the end as I got only the board so I can't test it.

    I replaced the 4x 6V 100uF caps by some solid polymer 16V 100uF, and the 13x 16V 10uF by some 10uF 1206 MLCC. The 2x 50V 1uF were replaced by some garbage through hole with the same ratings, I don't think it'll matter that much. The cap at C44 looked like it was ripped off, no idea what it was so left it off, I don't think it matters either.

    Anyway, since there doesn't seem to be any info on the web about this, I'm uploading pictures after the work and also the dump from the socketed EPROM (I removed it to clean the board so I thought why not dump it, if ever someone needs it they would be very happy to find it here…).

    HN27C4096AG-12_KR-370_70781789.BIN.zip
    Attached Files
    Last edited by piernov; 12-07-2023, 03:27 PM.
    OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

    #2
    Re: Roland KR-370 Main board

    These capacitors are absolutely notorious for destroying mid-90s Roland gear. Not that it matters much now but I can't help but wonder which manufacturer was responsible for this and if it's related to the quaternary ammonium salt formulas mentioned on this forum.

    There's a site that claims to have the service manual for this device but as they only seem to send it out in exchange for other service manuals I won't bother linking it here.

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      #3
      Re: Roland KR-370 Main board

      Follow-up on this one: it didn't work. Turned on fine, but no audio output at all.
      The owner tested the amp board by plugging in an external source and it was working, so the issue was most likely related to the digital control board that I worked on. They brought me the whole thing so that I could troubleshoot it (now I can't watch TV anymore but no big deal since I never turn it on anyway).

      Probed some stuff with the oscilloscope, basically the audio processor was generating the digital signal that goes into the DAC (NEC UPD63200), but there was nothing on the output of the DAC.
      I couldn't really find something wrong around it, although I kinda suspected the opamp (NEC µPC4570) might be a problem as well. There was a good amount of damage from the leaky capacitors in this area.
      So I went ahead and replaced both chips, and that indeed fixed the problem.

      Now everything seems to be working fine.
      https://youtu.be/sGoPKpv19sA
      Attached Files
      OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

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