[sdiy] Prophet 600 Syndrome ?

[Csaba Zvekan]

Hi Synthpeople,

After replacing various IC's, capacitors, CEM's I wonder if this what  
I am encountering is maybe "normal" for the Prophet 600.

When I tune the frequency higher than 6 on the OSCI B the Voice 3 B is  
not playing in tune in the higher octaves.


So then I have replaced the following :

1. All tantalum capacitors to electrolyte capacitors with  the  
equivalent value.

2. I replaced U416 the CMOS 4051 (even added a 0.1uF bypass capacitor)

3. Replaced all the 10nF capacitors  
(C423,C422,C421,C424,C417,C418,C419,C420)

4. Replaced the CEM3340 (VOICE  3B)

5. Replaced the CEM3372(VOICE 3)

6. All the 0.1uF caps around the VOICE 3

7. And of course OP-AMP U423 with TL-082



Still no Luck. I mean the synth performs and tunes very well except  
when you tune OSC B in a very high pitch.
I slowly wonder if that is limitation of something in the DAC or  
somewhere else. Since this is not making sense. All other voices play  
and scale fine in high pitch but that Voice 3B.
Before I troubleshoot any further can somebody who has a PROPHET 600  
confirm that this a known bug or otherwise let me know that the OSC B  
scales and plays fine in the higher octaves as well ?


Thanks

Csaba