[sdiy] Prophet 600 Syndrome ?

Thu Jun 5 17:57:04 CEST 2008

Yeah it is great. I was troubleshooting there for days replacing stuff  
that I didn't even have to. Then a very helpful person told me to  
measure things out rather than guessing around what IC might be bad or  
capacitor. It turned out he was right. It wasn't an IC nor a cap. It  
was a stupid resistor.
I was measuring the Output voltages of the associated OP-AMP U-423 pin  
7 and realized that the voltage was too high compared to the other  
voices. So I figured the problem can only be between the OP-AMP and  
the the CEM3340 's pin 15. and there is really not much circuitry  
left . Three resistors and a capacitor. When I measure the resistance  
on R456(but for Voice 3B I don't know the exact Rxxx) it was all  
clear. Something like 4M OHM instead of the 357K OHM . There had to be  
the error.
I replaced the resistor and scaled it fresh and it works now like a  
charm.
The good thing about the whole process is that the Power Supply  
section got brand new caps. And some other bypass capacitors and  
tantalum caps were also replaced.
I have ordered the diagnostic ROM and Schematics  from  
WineCountrySequential.com which are on the way to me :). Ohh well.

Thanks again

Csaba

On Jun 5, 2008, at 5:09 PM, Pete wrote:

> Hey thats great. How did you figure out it was the resistor? Good
> troubleshooting!
>
> pete
>
> On Thu, Jun 5, 2008 at 4:12 AM, Csaba Zvekan <czvekan at gmail.com>  
> wrote:
>> Thank you for all your help.
>>
>> This morning I have resolved my issue with my Prophet 600. The  
>> problem was a
>> resistor in the voltage divider section that goes straight into the  
>> summer
>> section of the CEM3340. I replaced the resistor with the same value  
>> and
>> voilà it was working again.
>>
>> Thank you again
>>
>> Csaba
>>
>>
>> On Jun 4, 2008, at 11:29 AM, Csaba Zvekan wrote:
>>
>>> LOL. thanks Pete :)
>>>
>>> So just go any preset turn the MIXER all the way to the right  
>>> (Clockwise)
>>> we want to exclusively listen to OSC B's . And then try to play  
>>> the last two
>>> octaves with frequency  set to 8 or even 10. Frequency on  
>>> Oscillator B.
>>> If it works I know I have a problem. Maybe the corresponding  
>>> CEM3372 is
>>> causing all that .I read something like that.
>>>
>>> I greatly appreciate it
>>>
>>> Csaba
>>>
>>> On Jun 4, 2008, at 7:21 AM, Pete wrote:
>>>
>>>> Honestly im pretty sure mine doesn't do what yours is doing, but im
>>>> willing to help you out since I have a p600. How do you test each
>>>> voice so I can try it?
>>>>
>>>> pete
>>>>
>>>> On Tue, Jun 3, 2008 at 1:35 PM, Csaba Zvekan <czvekan at gmail.com>  
>>>> wrote:
>>>>>
>>>>> 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
>>>>> _______________________________________________
>>>>> Synth-diy mailing list
>>>>> Synth-diy at dropmix.xs4all.nl
>>>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> http://www.myspace.com/23isgood
>>>
>>> **************
>>> http://www.csabazvekan.com
>>> music stuff
>>> http://www.csaba.ch
>>> electronic stuff
>>> http://www.synthmaniac.com
>>> synthesizer stuff (not fully set up yet)
>>>
>>>
>>>
>>>
>>>
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>>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>> **************
>> http://www.csabazvekan.com
>> music stuff
>> http://www.csaba.ch
>> electronic stuff
>> http://www.synthmaniac.com
>> synthesizer stuff (not fully set up yet)
>>
>>
>>
>>
>>
>>
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>
>
>
> -- 
> http://www.myspace.com/23isgood

**************
http://www.csabazvekan.com
music stuff
http://www.csaba.ch
electronic stuff
http://www.synthmaniac.com
synthesizer stuff (not fully set up yet)