D50 - loud noise from (almost) all outputs

[Pascal]

Hey!
All outputs but "Headphones left" of the stereo headphone output have kinda low Volume and you can hear a loud noise which changes volume pretty much randomly.

"Headphones left" only works, if you DO NOT connect a cable to "headphone right" ( that means: mono-cable in the stereo headphone output works fine, since it does only receive the left channel connecting a stereo-cable makes both of the channels sound bad).

Since I can't afford bringing it to a real synthesizer-guy who can repair it, I tried repairing the D50 by changing some parts. I changed the Volume- and Aftertouch-Sliders and all the outputs on the backside. Didn't fix anything. Then someone told me it might be the Amplifier chip ( i think it's IC 4570 on the Bender Board). Changed it and there's no difference as well.

I hope someone can help, send me your ideas please :)
btw, although i'm out of ideas, i can read the D50's circuit diagrams and will understand what you are telling me

thanks in advance!!!

[upunkt]

Few questions...
- Regarding the noise, is it more like static crackling or pure unmodulated white noise?
- You write the volume's changing randomly, but could you identify some kind of scheme?
- Is there any real D-50 sound or is it just noise?