[sdiy] Prophet 5 rev2 conundrum

Roman Sowa modular at go2.pl
Fri May 12 11:35:26 CEST 2023


A broken track or solder joint is the most difficult fault to find.
Especially when the PCB is the size of Wyoming with milion solder joints.

Roman

W dniu 2023-05-11 o 19:07, g m montalbano via Synth-diy pisze:
> 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 <mailto: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
>     <mailto: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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