Vintage Synth Repair

The control panel (micro computer system)is working. I am planning to 
set the ADSR soon. Right now I verified EQ board is good by injecting 
audio generator. I attached a schematic section to discuss a bug with 
the sequencer. Once I resolve this I should have a CEM3310 issue and 
I may have a P10. If anyone has a P10 schematic or wants to look at 
my attachment, I wanted to ask help with something. If I ground pin 1 
on the 4556B decoder the sequencer panel lights up and I hear the 
tape deck come alive. So I am not getting a logic Low out the gate 
feeding the decoder enable. This schematic is not like my Sequncer 
board schematic but basically my -IOREQ output from Z80 needs to go 
Low but is not. Not sure if this is still a hardware problem (which I 
see how) or a firmware issue EPROM.

I attached a schematic page in the Files section called P10 Sequencer


--- In vintagesynthrepair@yahoogroups.com, Stephen Jones 
<thirteentech@...> wrote:
>
> I would have to go look at the schematic, but from
> memory I think that it would work.
> 
> 
> --- Frank Simon <fsimon001@...> wrote:
> 
> > Thanks. Shouldn't I be able to Inject an audio
> > generator on the coax connecting the voice board to
> > the EQ board to prove the EQ board functional.
> >   ----- Original Message ----- 
> >   From: Stephen Jones 
> >   To: vintagesynthrepair@yahoogroups.com 
> >   Sent: Friday, June 06, 2008 5:56 AM
> >   Subject: Re: [vintagesynthrepair] Re: Prophet 10
> > dead
> > 
> > 
> >   No sound because no stored patches.
> > 
> >   Put your oscilloscope on some of the VCO wave
> > output
> >   pins and see if there is an audio waveform there.
> > If
> >   there is, play some keys and see if the frequency
> >   changes. If it doesn't, push the autotune button
> > and
> >   see if the VCO frequency sweeps as the auto tune
> >   process occurs. This will tell you if the computer
> > is
> >   talking to the sample and holds, and if they in
> > turn
> >   are driving the VCO's. 
> > 
> >   If you get that far, put your scope on the outputs
> > of
> >   the VCF's, and see if there is a signal there.
> > Before
> >   you do this make sure that you set up a basic
> > patch on
> >   the front panel with VCO's turned on, mixer up, no
> > VCO
> >   of VCF modulation, VCF cutoff open, resonance
> > down,
> >   zero attack and decay of the 2 ADSR's, and so on. 
> > 
> >   If there is filter output, move on to the voice
> >   channel VCA's, and finally the master VCA. The EQ
> >   board is another common failure. 
> > 
> >   --- fsimon100 <fsimon001@...> wrote:
> > 
> >   > I truly had a great day. I replaced a 1Kx4 RAM
> > and
> >   > resolved my 
> >   > computer problem on my P10. Now all LEDs light
> > up
> >   > and the unit 
> >   > behaves somewhat functional. Upon turn on the
> > unit
> >   > goes to tune cycle 
> >   > then all LEDs light up and entire panel is
> >   > functional. Still no sound 
> >   > but this is a great milestone. Two problems I
> > see
> >   > are sequential 
> >   > board is dead which I think I'm on top of. This
> > is
> >   > PCB9 which I over 
> >   > voltaged when I put the 12V regulator in instead
> > of
> >   > 5V (due to poor 
> >   > documentation this is an option for tape or
> > wafer
> >   > drive). I think 
> >   > this will be easy to fix but I was hoping to
> > help on
> >   > one clue. There 
> >   > is a window showing voices 1 thru 5 and below 6
> > thru
> >   > 10. The top 1 
> >   > thru 5 show 1,3, and 4 LEDs on continously never
> >   > changing. The bottom 
> >   > 6 thru 10 change as I hit the keys as if it is
> >   > responding however LED 
> >   > 7 never comes on. Can someone offer advice. I
> > have 4
> >   > CEM3310s out on 
> >   > the top voice board. It is to my understanding I
> > may
> >   > get a noise out 
> >   > if configured right to see functionality before
> > I
> >   > buy expensive chips.
> >   > 
> >   > Sorry long but I am very happy to be at this
> > status.
> >   > Can sequencer 
> >   > shut down operation. Was curious, should I get
> > sound
> >   > without 
> >   > sequencer.
> >   > 
> >   > 
> >   > 
> >   > --- In vintagesynthrepair@yahoogroups.com,
> > "Frank
> >   > Simon" 
> >   > <fsimon001@> wrote:
> >   > >
> >   > > I did find a chip pulling down DB4 on U311 it
> > is a
> >   > 6514 4K CMOS 
> >   > RAM. Thank god for IC sockets. The only problem
> > I'm
> >   > a little confused 
> >   > on a cross for it. It appears obsolete. It is
> > called
> >   > D444C on the 
> >   > chip and 6514 on schematic. Can anyone offer
> > advice
> >   > on a cross.
> >   > > ----- Original Message ----- 
> >   > > From: fsimon100 
> >   > > To: vintagesynthrepair@yahoogroups.com 
> >   > > Sent: Friday, May 30, 2008 8:58 AM
> >   > > Subject: [vintagesynthrepair] Prophet 10 dead
> >   > > 
> >   > > 
> >   > > Was curiouse if anyone can offer help. I
> > bought
> >   > a dead P10 no 
> >   > lights 
> >   > > or anything. The processor is good. I put
> > logic
> >   > analyzer on 
> >   > decoder 
> >   > > output and see ROM1 (Y0) and RAM (Y5)(which I
> >   > believe is the 
> >   > scratch 
> >   > > pad memory)active at start up. All address
> > buses
> >   > and Data buses 
> >   > are 
> >   > > active. I am not certain the algorithm. A flow
> >   > chart would be 
> >   > nice or 
> >   > > some help with what I should see at some
> >   > critical points. I am 
> >   > > wondering if there is a chance the ROMs lost
> >   > programming and how 
> >   > would 
> >   > > I know. Even if they did shouldn't lights
> > and/or
> >   > display come on. 
> >   > And 
> >   > > yes the power supplies are good.
> >   > >
> >   > 
> >   > 
> >   > 
> > 
> > 
> > 
> >
>