Synth: Dsp overheating and passing no sound

Discussion in 'General Electronics Chat' started by omaroski, Oct 28, 2012.

  1. omaroski

    Thread Starter Active Member

    Jun 19, 2008

    i recently got this not working Korg Microkorg synthesizer which i'm trying to fix.


    The owner (or who for him) made a mess in the psu circuitry with the soldering iron in his hand, burning tracks and components. I replaced what was missing, a p-channel mosfet in the digital 3.3v supply and connected back the tracks.

    Finally it powers on, both the 3.3v and 5v are there, all the leds, display, buttons seem to work as they should but the only sound coming out from the outputs is some low freq tone/hum not very musical at all, playing with knobs, keys, buttons won't ''shape'' it or play in any way. After some time the noise went away.

    Later on i noticed heat coming from the dsp56362 chip, i placed my fingertip on the case and it was quite burning! I tried to blow cold air over it and the noise came back once again.

    I tried the full test (auto) described in the manual and it was telling me E.2.1 flashing on the display, would be nice to know what this stands for.

    Can you help me define whether or not the problem is in the dsp?

    Thank you a lot!
  2. SPQR


    Nov 4, 2011
    This is a tough one.
    I've been in this situation before, and it's possible to trash a circuit board trace in another layer if the person soldering has been too "vigorous".

    You could try checking voltages on some of the pins to determine that everything is fired up correctly.

    If you have a scope, you could snoop around and see if there are any waveforms coming out of pins where they should come out (you'd have to look at the datasheets for the chips). could go to the Korg Discussion Forum, join, and ask them.

    I already did a search on their forum, and could not find any mention of "E.2.1"

    Let's see what others might say.
  3. omaroski

    Thread Starter Active Member

    Jun 19, 2008
    Thank you for your reply.

    There's like a crater where the transistor usually used to be!

    I checked all the vcc voltages and it seems that is being fired up correctly (the word fire is too much correct from the heat it's producing!), i'll check it again.

    Yes i have a scope and i was looking for waveforms, i could identify a triangle wave but can't remember if it was on pin1 or 2 (i didn't have computer and datasheet at hands).
    Looking at the datasheet would make sense on pin1 since it is the clock from the cpu chip for spi (or I2C?) communications while pin2 is the slave select control state.

    I should check if it's putting something out from the DAX i guess?

    Yes i tried the search function on the korg forum but couldn't find many topics related to electronics.

    For what it ever might mean i can suppose Error 2.1 or voltage 2.1 indicating that is low somewhere, possible or absurd i don't know.