PC361 weird noise


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Hi all,

I bought used PC361... Little story - you can skip next paragraph.

The instrument came from seller in Italy and was unfortunately broken from shipping. Because of that, I needed some keys to replace. I did all repairs, changed almost all screws (the used ones was in terrible condition). But after making it mechanically working, there was something interesting. In the setup was transposition -5 semitones, but playing was as expected, only without dynamics in right side (half keyboard). And while startup, it recognized 88key mechanics... Research continued. After I get the service manual, I realized the wrong diode option on key scanner pcb (one was poorly soldered by hand). After soldering done by myself, the kurz see 61key Fatar Tp09 as expected. WOW. but the dynamics on right half is still gone and it fires full power. When I switched the two ribbons, it definitely led to the HW problem. And I realized, that the rubber switches were turned wrong. So I turned them as like the bass ones was on the other PCB and then FINALY everything seems to be ok, but.

Not from start, because there were only short how it works turn on's, but later, while I tried to find out the soldering solution and other things... There comes some weird and loud noise from the outputs. I tried of course reconnecting all the multipins inside. Here is more desrcibtion...
The noise:
  • Is louder than the sounds
  • Is dependent on volume potentiometer (which is only ADC controller)
  • Comes randomly in and out
  • Is dependent on preset changes (when i switched from lead to piano for example, it changes in character/volume/dissappear all the way), but can return instantly when I turn the previous preset
  • goes thru FX. If I disable all effects, the noise is dry, FX on - lot of reverb and other default effects (depending on preset of course)
  • Comes from the core, definitely, based on this research.
  • Is like a modulated white noise with random volume, sometimes with "shot" endings, sometimes with weird artefacts. I attached some sample of it. Sometimes it repeats, sometimes i am surprised with new one :(

Factory reset did not help. Please, if you think you know who knows, or you know, let me know to know how to break finaly this issue.

Thank you guys!

https://soundcloud.com/tom-ku-era-997260645%2Fkurzweil-issues%2Fs-BI21EHH8DHI
 
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happyrat1

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Check the electrolytic caps in the output sections with an ESR meter to see if any are going bad.

It sounds like filtering noise to me.

Gary ;)

What does it sound like thru headphones?
 
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It sounds the same, I tried to record wia headphone output and main output, the same results. I don't think it is HW relevant, because this should be not dependent on volume potentiometer, but it is. I can check it anyway :)
 
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happyrat1

Destroyer of Eardrums!!!
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I would still suspect output stages filter caps, considering the age of the unit and the condition you restored it from.

Gary ;)
 

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