Monday, October 14, 2013

Roland KR650 repair: bad electrolytic capacitors


This particular model suffers from leaky electrolytic capacitors on the main board. By leaky, I don't mean electrically; I mean there is some nasty liquid leaking out of these things! The result is all kinds of distortion in the outputs, low volume, intermittent problems, etc.

I have repaired a few of these. The repair has always been permanent, however on most instances the liquid that leaks from the capacitors burns through traces on the board. On this one, the liquid burnt out the V- supply to one of the op amps near the DAC chips.



So, the repair consisted of removing all the surface mount electrolytics on the main board, cleaning up all the liquid, replacing the caps, and repairing a trace that supplies the V- to one of the op amps near the DACs.  Other traces may be damaged too, so if it still doesn't work when you replace the caps you will have to check the traces that run near them.

I used standard through hole caps instead of surface mount on this job. I bent the leads and attached them to the pads; there is plenty of room for this, and I applied a bit of hot glue on the leads to hold them in place. If my memory serves, they were all 3.3 and 10uF caps.



The instrument sound great now. I also replaced all the tact buttons. There sure are a lot of buttons on that thing!


Finally, the contacts on this one were good. However, I think this was a transitional model, and the key contacts are no longer available. This may be a consideration in judging the cost effectiveness of repairing this model; if the contacts show signs of failing, it would be worth trying to repair them first (perhaps by recoating them) before investing time and money in fixing the other issues.

The highlighted area is where I found destroyed traces, supplying the V- to one of the SMT op amps near the DACS
.

4 comments:

  1. You are heaven sent. I have the exact model and looks like there is hope for it now. Can I send you the mainboard for repair? If so, How much? Thank you and God bless.

    ReplyDelete
  2. Hi,
    I have the Roland KR-5500 and it has the same problem. After I replaced all the Caps it wont start. No lights and no signs of life. Any suggestions?
    Thanks

    ReplyDelete
  3. I have the same problem so I am going to tackle replacing the caps.

    ReplyDelete
  4. Hi,
    I have a kr-4500 - very similar- The right ouput sound is awfully crackling. I just replaced ALL capacitors of the mainboard and have the same result , no improvement...Could it be the power board ??

    ReplyDelete