[sdiy] prophet 600 -- tough problem

[Clint Davis]

00X00XOO XOOXOOXO

looks like octal backwards to me.  I don't know if that helps or if it's
even correct, but it appears to be the most significant bit of all the octal
numbers being bad.  I think that octal was pretty popular when that synth
was made (as opposed to Hex).  Are there any 3 bit address lines?  That's
where I think I'd look.

Clint


----- Original Message -----
From: "greg montalbano" <greg.montalbano at ucop.edu>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, June 04, 2002 3:46 PM
Subject: [sdiy] prophet 600 -- tough problem


> Hi--
> I'm hoping to hear from anyone who has specific, detailed knowledge of the
> workings of the digital portion of this synth.
> I have several control voltages that are completely screwed;  but the
> problem is definitely upstream from the four 4051 demultiplexers*.
Looking
> at the outputs of those four ICs in order (on schematic "Board 4, page 1
of
> 4"), the bad CVs form a pattern: 00X00XOO XOOXOOXO etc etc, where O= a
good
> CV and X= a bad one.  This leads me to suspect a problem with the data or
> address lines controlling the DAC and/or demultiplexers;  can anyone tell
> me exactly what to look for and where to look?
> Everything else on the synth is functioning correctly & consistently.
>
> Thanks.
>
> ~GMM
>
> *This was determined by removing them & testing them out of circuit;
while
> they were removed, I also tested each of the voice S&Hs  with a known CV
> and found them to respond correctly.
>