[sdiy] Prophet 5 rev2 conundrum

Jimmy Moore jamoore84 at gmail.com
Thu May 11 20:29:42 CEST 2023


How did you end up finding the crack?

On Thu, May 11, 2023, 11:13 AM g m montalbano via Synth-diy <
synth-diy at synth-diy.org> 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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