[sdiy] Prophet 5 rev2 conundrum

Oren Leavitt obl64 at ix.netcom.com
Fri May 12 03:30:10 CEST 2023


Good work! Always a relief when a trivial (albeit elusive!) cause is found.

I had a similar issue with a Roland MSQ700 MIDI sequencer where it was 
not responding to some of the push buttons. Turned out to be a few 
invisible hairline cracks running thru the front panel PCB.

- Oren

On 5/11/23 12:07 PM, g m montalbano via Synth-diy wrote:
> Finally solved this -- and I'm sorry to say it's not very interesting.
>
> There was a microscopic break in one of the ground traces going to the 
> 60 pin connector on the voice board. When pressing the meter probe to 
> it, it made contact and showed as good; with the probe removed, 
> contact was lost, and the tune circuit was lost.
>
> Hope to come up with something more interesting & illuminating next time.
>
> Thanks to everyone who contributed ideas.
>
> ~GMM
>
> On Wed, May 3, 2023 at 8:32 PM Michael E Caloroso 
> <mec.forumreader at gmail.com> wrote:
>
>     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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