Prophet 600 Oscillator B issue

Hello! I have a Prophet 600 with a strange problem tied to the amp EG release. I made a short video rather than having to explain it all in a forum. Any thoughts would be welcomed. Thanks!

I’m not familiar with the P600 but sounds like every 6th note has the issue which suggests the problem is isolated to one voice. Can you disable all voices except for one at a time to confirm this? My hunch is that it’s something in the DAC sample & hold area.

Good suggestion! I’ll see what I can do. We decided today to recap the whole board since we’re going to be in there anyway. That might fix this problem. I’m going to try your suggestion though - thanks again!!

Keep us posted please.

Sorry - it appears the notification system isn’t working so I didn’t see your last message. I’ll certainly keep everyone in the loop. Capacitor kit arrived over the weekend and this will be our next project to tackle. We’ve been redoing a JD-800 with the red glue issue and it’s almost complete!

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Replaced all the caps today with no improvement. More troubleshooting ahead!

So here’s the latest. It does appear that oscillator B, voice 6 is not working properly. When we take the Gligli mod out and put the original Z80 back in the issue resolves itself, though we also lose the benefits of the Gligli. Currently trying to contact anyone with knowledge of that mod to see if they have any thoughts/ideas. We flashed the software to see if that helped but it did not.


Did you have any errors running the self-tune?
Have you tried contacting Synthchaser?

My guess would be something wrong with the Teensy board. I would resolder the headers and check those flying wires. The flying lead connecting to pin 30 is also a concern.

Thanks! We tried Synthchaser and he recommended a forum to try and get some help. Resoldering the headers is a good idea and we can take a look at pin 30 as well. Thanks for the tips and I’ll post back once we’ve tried them.

Lots of troubleshooting and tracing since last post. It appears that there is bad data being sent to the DAC from the Gligli processor. We were able to view the data on a logic analyzer which is how we arrived at this conclusion. Just wanted to close the book on this and let everyone know what we found. Thanks to all who chimed in!

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I was in the ballpark! :sunglasses:

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