[sdiy] Prophet 600 Syndrome ?

[JH.]

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

I have zero experience with the Prophet 600.
But as a general rule, if you replace a Tantal *bypass* cap with an 
(aluminium) electrolytic, you should connect a 100nF ceramic in parallel.

Maybe something that has been stable with tantalums, now oscillates with 
just the aluminium electrolytics, and it *could* cause a symptom that you 
describe.

It may be far-fetched, it's probably not likely, but it's possible.

JH.


----- Original Message ----- 
From: "Csaba Zvekan" <czvekan at gmail.com>
To: <Synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, June 03, 2008 10:35 PM
Subject: [sdiy] Prophet 600 Syndrome ?


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
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