WTB: CEM3320 & CA3280 (Was: [sdiy] Prophet 5 question)

[Karl Ekdahl]

Hi all

Subject says it all. One of several problems in the prophet was these two ICs going bad, the bad CA3280 killed the CEM3320 it seems.

Thanks

Karl

--- Den fre 2009-04-03 skrev Tom Wiltshire <tom at electricdruid.net>:

> Från: Tom Wiltshire <tom at electricdruid.net>
> Ämne: Re: [sdiy] Prophet 5 question
> Till: "Karl Ekdahl" <elektrodwarf at yahoo.se>
> Kopia: synth-diy at dropmix.xs4all.nl, "Barry Klein" <Barry.L.Klein at wdc.com>
> Datum: fredag 3 april 2009 21.54
> 
> On 1 Apr 2009, at 23:44, Karl Ekdahl wrote:
> 
> > 
> > Hi list
> > 
> > I found the culprit to be a single last tantalum i had
> not seen earlier, of course it was the one that was dead.
> > 
> > Right now the synth makes sound, but it's weird; the
> keys are working very on/off, different keys will not work
> at different time just to start working all of the sudden.
> I've checked the mechanics and they all measure fine, i've
> also reseated the keyboard ribbon cable several times. I'm
> starting to wonder if there's something up with the keyboard
> scanning circuitry.
> > 
> > Another problem i have is that oscillator A is very
> faint on all voices, i can hear it if i turn down oscillator
> B all the way - and it's the same for all voices. I'm
> guessing there's some mixing circuitry common for all voices
> that i need to look at.
> > 
> > Karl
> 
> Karl,
> 
> There's no mixing circuitry that would account for all the
> oscillator A's being quieter. Osc A and B are mixed in each
> voice before being fed to the filter. Consequently, I'd look
> at the CV circuitry for the mixer CVs. The two oscillator
> signals are mixed by a CA3280 wired up as two VCAs. The
> "oscillator amount CV"s for both oscillators are common for
> all voices, so this would explain the symptoms you're
> seeing.
> 
> Regards,
> Tom
> 
> 
> 
> 
> 


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