[sdiy] Prophet 5 rev2 conundrum

g m montalbano montalbanogm at gmail.com
Tue May 2 23:57:23 CEST 2023


Yes, all ten oscillators are working correctly.

On Tue, May 2, 2023 at 11:59 AM Ian Fritz <ijfritz at comcast.net> wrote:

> Is the oscillator itself stable?
>
> > On May 2, 2023, at 10:42 AM, g m montalbano via Synth-diy <
> synth-diy at synth-diy.org> wrote:
> >
> > 
> > I've been working on these for twenty years, and thought I'd seen pretty
> much everything that could go wrong with them.
> > Now, I have one that works perfectly except for the fact that it will
> not go through the tune procedure, either at powerup or when the Tune
> button is pressed.
> >
> > The confusing part is that the fault has been narrowed down to the voice
> board: if I swap in a working voice board, the unit functions correctly; if
> I install this voice board in another unit, the problem follows.
> >
> > As far as I can see, the ONLY parts on the voice board that relate to
> tuning are the two 4051 multiplexers (U423 and U428) and the LM311
> comparator (and its associated resistors & caps). All of these components
> have been replaced; traces and resistors have been checked &  measured. All
> traces to the 60 pin connector between the CPU and Voice boards are good,
> as is the 60 pin cable.
> > EVERYTHING is there, and everything works correctly except for Tune.
> >
> > I've been hitting my head against this for a couple of weeks, and would
> appreciate any suggestions as to where to look.
> >
> > Thanks.
> > ~GMM
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