[sdiy] Prophet 5 rev2 conundrum

Michael E Caloroso mec.forumreader at gmail.com
Thu May 4 05:32:36 CEST 2023


Short the TUNE button contacts.  This will loop the autotune process then
you can start probing on the 'scope.

I know that a DC offset at the audio autotune summing buss will mess up the
autotune algorithm.  Check each voice audio at the summing buss for DC.

MC

On Wed, May 3, 2023 at 9:23 PM brianw <brianw at audiobanshee.com> wrote:

> Indeed. Tests have confirmed that the EPROM chips (I think there are
> three) have the full and uncorrupted tuning subroutines in them, because
> the same digital CPU board can tune a known-good analog Voice board.
>
> You're lucky to have spare working P5R2 boards for these diagnostics
> (despite the frustration so far).
>
> Brian
>
> On May 3, 2023, at 3:45 PM, g m montalbano wrote:
> > All very true. However, the problem isn't on the CPU board, since that
> board works correctly with another Voice board.
> > The power supply, front panel,CPU board and 60 pin cable are all good
> --the fault is on the Voice board.
> >
> > On Wed, May 3, 2023 at 2:49 PM Jay Schwichtenberg wrote:
> >> For somethings not in the analog realm.
> >>
> >> One of the first things to check in old systems like these after the
> >> power supplies is the reset circuit.
> >>
> >> If I remember correctly there are multiple EEPROMs in it. Could be the
> >> tuning code in one of them could of gone bad. EEPROMs don't last
> forever
> >> and if the code is bad the processor would wonder off into oblivion.
> >>
> >> Might very carefully pull the EEPROMs and reseat them to see if a
> socket
> >> connection might of gone bad too.
> >>
> >> These are they types of problems logic analyzers are good for. Big pain
> >> to setup but the problem maybe a lot easier to find.
> >>
> >> Jay S.
> >
>
>
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