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 Forum index » DIY Hardware and Software » The Repair Shop
Kawai SX 240 - CPU noise infiltration - i'm scared
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ALAS



Joined: Oct 14, 2013
Posts: 11
Location: Philadelphia

PostPosted: Wed Feb 24, 2016 8:50 pm    Post subject: Kawai SX 240 - CPU noise infiltration - i'm scared Reply with quote  Mark this post and the followings unread

i'm struggling to figure out how to deal with a prohibitive noise problem in my Kawai SX 240. i got the synth about a year and a half ago in a somewhat unreliable condition and with a lot of cleaning, replacing the battery and all the switches it was working perfectly until this problem arose recently. it was intermittent at first but is now constant. it is a crunchy, pulsating scraping noise in the background of every patch, loud enough to obscure the main sound when playing a chord. listening around inside with a signal trace, i tracked it to the "slave CPU" which apparently handles the patch editing controls. it is somehow making its way into the audio signal path. the output of the oscillators themselves are clean but by the time the signal gets to the filter the noise is there.

An interesting thing about it is that when I do any parameter editing, the noise disappears briefly from the synth's main audio output. Listening to the CPU directly, I noticed that the pulsating quality of the noise stops for a few seconds after i change one of the parameter controls. I guess when the CPU is "busy doing something" the noise it produces is different.

I'm not sure whether the noise is supposed to be coming out of the CPU at all or not, but the fact that it briefly disappears from the synth's main audio output when the noise stops pulsating at the CPU suggests that it is the pulsation/modulation itself that might be the problem.

Is that analysis correct?
I have some experience with troubleshooting analog circuitry but don't know anything about digital stuff, the "brains" of synths, so any ideas of what might be going on would help.

I am really anxious to fix this synth because it is my main and only polysynth and I rely on it for everything. I have shows coming up and I am going to be going on tour with it soon! I am scared that the CPU might be dying in which case game over, right?

Last edited by ALAS on Wed Feb 24, 2016 10:59 pm; edited 1 time in total
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ALAS



Joined: Oct 14, 2013
Posts: 11
Location: Philadelphia

PostPosted: Wed Feb 24, 2016 9:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

actually it now seems like the noise has suddenly gotten significantly quieter for no discernible reason. It was still loud when i last turned off the synth. a half hour later (after writing my first post) i came back and turned it on and the crunchy noise was barely audible. i'm sure it's no thanks to anything i did. i listened to the noise right out of the CPU and couldn't tell whether it was any different. what does it all mean?
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blue hell
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Joined: Apr 03, 2004
Posts: 24079
Location: The Netherlands, Enschede
Audio files: 278
G2 patch files: 320

PostPosted: Thu Feb 25, 2016 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

It may be picking up noise from an external source?

Try to move the synth around, disconnect MIDI, try another power outlet .. stuff like that .. just to investigate.

_________________
Jan
also .. could someone please turn down the thermostat a bit.
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